Slow-Onset Versus Rapid-Onset Hazards

The distinction between slow- and rapid-onset hazards is useful because the methods to deal with them often differ. Rapid-onset hazards often occur with violent intensity and have profound effects on the surrounding environment, resulting in measurable numbers of casualties and damage. Slow-onset climatic changes brought on by deforestation, drought, desertification, or environmental pollution change the suitability of different parts of the world for human habitation, and they affect agriculture and flora and fauna. The effects of slow-onset disasters are often insidious. Their impact can be measured only through environmental studies and in terms of reduction in quality of life and productivity for the affected population. As discussed later, slow onset hazards rarely are identified as disasters or emergencies, although their impacts may be greater or similarly widespread. Variables include levels of public attention to the hazards and the ability of the government to deal with them. Typically, threats become mitigated by slow movement away from hazards; for example, many of the 11,000 residents of the Pacific island nation of Tuvalu have left the country because the island is being swallowed by sea level rise.

Conservatively, an estimated 1.5 million to 2 million people have been killed in rapid-onset disasters since 1946—an average annual death toll of 35,000 to 50,000. The primary killers are earthquakes, tropical cyclones, and floods. Most deaths are concentrated in a relatively small number of communities, predominantly in poorer nations of Africa, Asia, Latin America, and Oceania. In comparison, North America, Europe, Japan, and Australia have average annual death tolls that rarely exceed a few hundred persons. In terms of total numbers of disasters worldwide, during the period from 1991 to 2005, flood disasters occurred most frequently, followed by hurricanes or cyclones and other windstorms.

Although comprehensive data for economic losses from rapid-onset hazards are difficult to obtain, a few examples illustrate the scale of the problem. Annual worldwide losses from tropical cyclones are estimated at between $6 billion and $7 billion. For landslides, the comparable figure exceeds $1 billion. These figures only hint at the impact of such disasters on the affected human population. The eruption of Colombia’s Nevado del Ruiz volcano in 1985 killed approximately 22,000 people and left 10,000 more homeless. An earthquake in Bam, Iran, in December of 2003 claimed at least 30,000 lives and destroyed 80% of the city. The 2005 Atlantic hurricane season caused record damages of $100 billion. Hurricane Katrina alone, in August of 2005, killed 1417 people in three U.S. states, displaced 1.5 million, and caused $75 billion in damages.

The relative human, economic, and social impacts of rapid-onset disasters are usually greatest in smaller, poorer nations. The 1985 earthquake in Mexico City caused economic losses equivalent to about 3.5% of Mexico’s gross national product (GNP). Hurricane Allen in 1980 caused losses in St. Lucia equivalent to 89% of this island nation’s GNP and destroyed 90% of its banana crop, which normally accounts for 80% of the country’s agricultural output. One of the strongest storms in recent history, Hurricane Mitch in 1998 devastated the economies and infrastructure of Honduras and Nicaragua.

Economic losses from rapid-onset hazards are increasing at a fast pace. In the United States, damage to buildings from earthquakes, tropical cyclones, and floods was estimated to increase from approximately $6 billion in 1978 to more than $11 billion in 2000 without additional loss reduction measures. At this same time, it was estimated that a major earthquake in Tokyo would probably kill more than 30,000 people, cause the collapse of 60,000 houses, and set fire to more than 400,000 homes.

Slow-onset disasters take an even greater toll, but precise figures are difficult to establish. Drought currently affects more people than does any other disaster; worldwide, it is estimated that droughts affected more than 18 million people each year during the 1960s, more than 24 million people during the 1970s, and 101 million between 1980 and 1989. During the early 1980s, drought affected up to 30 million people in Africa alone. In the United States, drought leads in economic impact, causing losses of $6 billion to 8 billion per year. Worldwide, droughts have led to famines, resulting in large numbers of deaths and displacements. Increasing desertification in arid areas may be contributing to droughts. Desertification, or decline in biologic productivity, extends to 70% of total productive arid lands (3.6 billion acres worldwide) and may adversely affect the quality of life for 10% of the world’s population, including urban dwellers.

Possible global warming is predicted to occur over the next 100 years as a result of increased atmospheric carbon dioxide caused by the burning of fossil fuels, deforestation, and generation of methane. If this occurs, sea levels will rise and coastal cities worldwide will be inundated. A rise of 1 m (3.3 feet) in sea level could flood 15% of arable land in Egypt’s Nile Delta and completely submerge the tiny islands of the Maldives, currently inhabited by 200,000. Hundreds of millions of people will also be affected if increased ultraviolet radiation is delivered to the earth’s surface as a result of stratospheric ozone depletion caused by continued release of chlorofluorocarbons.

Although global warming and ozone depletion are threats that may become more evident in the future, other forms of environmental pollution, such as water and air pollution, have immediate effects on life today. Massive oil spills, such as the 2010 leakages in the Gulf of Mexico, make headlines, and adverse health effects are seen from contamination and smog. Deforestation, particularly in the tropical rainforests, is highly significant. In addition to its contribution to possible global warming, the loss of forested land increases vulnerability to droughts, landslides, and floods.

Assessing Vulnerability and Risk

Not all hazards become disasters. Whether or not a disaster occurs depends on the magnitude, intensity, and duration of the event and the vulnerability of the community. For example, a severe earthquake is not a disaster unless it significantly disrupts a community by creating large numbers of casualties and substantial destruction. Effective disaster risk management requires information about the magnitude of the risk faced and how much importance society places on the reduction of that risk. Risks are often quantified in aggregated ways (e.g., a probability of 1 in 23,000 per year of dying in an earthquake in Iran). The importance placed on the risk for a hazard is likely to be influenced by the nature of the risks faced on a daily basis. For instance, in Pakistan, where communities are regularly affected by floods, earthquakes, and landslides, people use their meager resources to protect against what they perceive to be the greater risks, such as disease and irrigation failure. In California, where risk for disease is low, communities choose to initiate programs against natural disasters.

Vulnerability is often measured as the susceptibility of buildings, infrastructure, economy, and natural resources to damage from hazards. Many aspects of vulnerability, however, cannot be described in monetary terms and should not be overlooked. These include personal loss of family, home, and income, along with related human suffering and psychosocial problems. Although communities in developed nations may be as prone to hazards as those living in poorer nations, wealthier communities are often less vulnerable to damage. For example, although both southern California and Managua, Nicaragua, are prone to earthquakes, California is less vulnerable to damage because of strictly enforced building codes, zoning regulations, earthquake preparedness training, and sophisticated communications systems. In 1971, the San Fernando earthquake in California measured 6.4 on the Richter scale but caused minor damage and 58 deaths, whereas an earthquake of similar magnitude that struck Managua, Nicaragua, 2 years later reduced the center of the city to rubble, killing approximately 6000 people. Similarly, in wealthy countries, drought and resulting loss of food production and groundwater are managed by use of food surpluses and treated water, but drought in poor nations often leads to deaths from famine, as well as sickness and death from contaminated water supplies.

Disaster Mitigation Strategies

Mitigation involves not only saving lives and reducing injury and property losses, but also reducing the adverse consequences of hazards to economic activities and social institutions. Where resources are limited, they should be directed toward protecting the most vulnerable elements. Vulnerability also implies a lack of resources for rapid recovery.

For most risks associated with natural geophysical hazards, such as volcanic eruptions, tsunamis, and tropical cyclones, little or no opportunity is available to reduce the hazard itself. In these cases, the emphasis must be placed on reducing the vulnerability of the elements at risk. However, for technologic and human-made hazards or slow-onset hazards, such as environmental pollution and desertification, reducing the hazard is likely to be the most effective mitigation strategy.

Actions by planning authorities to reduce vulnerability can be active, in which desired actions are promoted through incentives, or passive, in which undesired actions are prevented by use of controls and penalties. Discussion of mitigation options follows.

Nature of Hazards

Some hazards exist naturally, and others are partially rooted in natural systems. Many of these occur infrequently or affect only small populations. One example is the eruption of toxic gases from several volcanic lakes in Cameroon that killed 2000 people in 1984 and 1986. Other rare events, such as meteor impacts, may occur only once every few centuries. Additional widespread but minor phenomena that damage property but do not generally cause loss of life include land subsidence and sinkholes. Some hazards, such as snowstorms, often occur in areas that are prepared to deal with them, and thus they rarely become disasters.

This chapter discusses hazards that affect large populations and that can be categorized as follows:

To plan appropriate responses to implement emergency medical care and other measures to save or restore physical and mental health of affected populations, governments and communities first need to understand the causal phenomena, characteristics, and predictability of the hazards and the factors that contribute to vulnerability. Examination of the hazard’s effects on humans, property, and the environment can promote measures to prevent or lessen casualties and destruction.

Causal Phenomena

The earth’s crust is a rock layer varying in thickness from a depth of about 10 km (6.2 miles) under the oceans to 65 km (40.4 miles) under the continents. The theory of plate tectonics holds that seven major and about six minor crustal plates, varying in size from a few hundred to many thousands of kilometers, “ride” on the earth’s mobile mantle. When the plates contact each other, stresses arise in the crust. Stresses occur along the plate boundaries by pulling away from, sliding alongside, and pushing against one another. All these movements are associated with earthquakes.

Faults are areas of stress at plate boundaries that release accumulated energy by slipping or rupturing. Elastic rebound occurs when the maximum point of supportable strain is reached and a rupture occurs, allowing the rock to rebound until the strain is relieved (Figure 89-1). Usually, the rock rebounds on both sides of the fault in opposite directions. The point of rupture is called the focus and may be located near the surface or deep below it. The point on the surface directly above the focus is termed the epicenter (Figure 89-2).

FIGURE 89-1 Elastic rebound in earthquake. A, Forces build up over time. B, Crust deforms. C, Crust snaps. D, Plates slide.

FIGURE 89-2 Motion of the earth’s plates causes increased pressure at faults where the plates meet. Eventually, the rock structure collapses, and movement occurs along the fault. Energy is propagated to the surface above and radiates outward. Waves of motion in the earth’s crust shake landforms and buildings, causing damage.

(Courtesy Disaster Management Center, University of Wisconsin.)

The energy generated by an earthquake is not always released violently and can be small or gradual. Minor Earth tremors are recorded daily in the United States, but whether these are caused by the same processes that can level a city is not known. Most damaging earthquakes are associated with sudden ruptures of the crust.

Characteristics

The actual rupture process may last from a fraction of a second to a few minutes for a major earthquake. Seismic (from the Greek seismos, meaning “shock” or “earthquake”) waves are generated. These last from less than one-tenth of a second to a few minutes and cause ground shaking. The seismic waves propagate in all directions, causing vibrations that damage vulnerable structures and infrastructure.

There are three types of seismic waves. The body waves (P, or primary, and S, or secondary) penetrate the body of the earth, vibrating quickly (Figure 89-3). P waves travel at about 6 km per second (kps) (3.7 miles per second [mps]) and provide the initial jolt that causes buildings to vibrate up and down. S waves travel about 4 kps (2.5 mps) in a movement similar to the snap of a whip, causing a sharper jolt that vibrates structures from side to side and usually resulting in the most destruction. Surface waves (L waves) vibrate the ground horizontally and vertically and cause swaying of tall buildings, even at great distances from the epicenter.

FIGURE 89-3 A, Propagation of seismic waves in an earthquake. Surface waves vibrate the ground horizontally (B and C) and vertically (D and E).

Earthquake focus depth is an important factor in determining the characteristics of the waves. The focus depth can be deep (from 300 to 700 km [186 to 435 miles]) or shallow (less than 60 km [37 miles]). Shallow-focus earthquakes are extremely damaging because of their proximity to the surface. The earthquake may be preceded by preliminary tremors and followed by aftershocks of decreasing intensity.

Earthquake Scales

Earthquakes can be described by use of two distinctly different scales of measurement demonstrating magnitude and intensity. Earthquake magnitude, or amount of energy released, is determined by use of a seismograph, which records ground vibrations. The Richter scale mathematically adjusts the readings for the distance of the instrument from the epicenter. The Richter scale is logarithmic; an increase of one magnitude signifies a tenfold increase in ground motion, or about 30 times the energy. Thus an earthquake with a Richter magnitude of 7.5 releases 30 times more energy than one with a 6.5 Richter magnitude. The smallest quake to be felt by humans was of magnitude 3. The largest earthquakes that have been recorded under this system are 9.5 (Chile, 1960) and 9.25 (Alaska, 1969).

The moment magnitude scale is a successor to the Richter scale and is most often used to estimate large earthquake magnitudes. Theoretically, all magnitude scales should yield approximately the same value for any given earthquake. However, controversy exists over the measurement of the great Indian Ocean earthquake that occurred on December 26, 2004, generating a tsunami that killed more than 280,000 people. The Pacific Tsunami Warning Centre (PTWC) estimated the magnitude as 8.5 on the Richter scale shortly after the earthquake. The U.S. Geological Survey (USGS), using the moment magnitude scale, increased its estimate from 8.1 to 9.0 Other scientists, using moment magnitude, have revised the estimate to 9.3, and the PTWC has accepted this, but the USGS has so far not changed its estimate of 9.0. The most definitive estimate so far has put the magnitude at 9.15.

The earthquake intensity scale measures the effects of an earthquake where it occurs. The most widely used scale of this type is the modified Mercalli scale, which expresses the intensity of earthquake effects on people, structures, and the earth’s surface in values from I to XII (Table 89-1). Another, more explicit, scale used in Europe is the Medvedev-Sponheuer-Karnik (MSK) scale.

TABLE 89-1 Modified Mercalli Intensity Scale of 1931

Location and Predictability

Most earthquakes (95%) occur in well-defined zones near the boundaries of the tectonic plates. These areas bordering the Pacific Ocean are called the circum-Pacific belt. Areas traversing the East Indies, the Himalayas, Iran, Turkey, and the Balkans are called the Alpide belt. Earthquakes also occur along the ocean trenches, such as those around the Aleutian Islands, Tonga, Japan, and Chile and within the eastern Caribbean. Some earthquakes occur in the middle of the plates, possibly indicating where earlier plate boundaries might have been. These have included the New Madrid earthquake in 1811 and the Charleston earthquake in 1816 in the United States, the Agadir earthquake in 1960 in Morocco, and the Koyna earthquake in 1967 in India.

Earthquake prediction was a constant preoccupation for early astrologers and prophets. Some signs of earthquake noted by observers were buildings gently trembling, animals and birds becoming excited, and well water turning cloudy and smelling bad. Although some modern scientists claim ability to predict earthquakes, the methods are still controversial. For example, the 1995 earthquake in Kobe, Japan, which killed more than 5000 people, was not predicted. However, mechanical observation systems make it possible to issue warnings to nearby populations immediately after detection of an earthquake. Reasonable risk assessments of potential earthquake activity can be made with confidence based on the following:

The island of Hispaniola, shared by Haiti and the Dominican Republic, has a history of destructive earthquakes. In January 2010, a magnitude 7.0 earthquake occurred approximately 25 km (16 miles) west-southwest from the capital city Port-au-Prince at a depth of 13 km (8.1 miles). Two years before this, scientists had detected signs of growing stresses in the fault that forms a boundary between the Gonave microplate and the Caribbean plate to the south, specifically the Enriquillo-Plantain Garden fault system, which includes much of Haiti. They warned Haitian officials that the fault was capable of causing a 7.2 magnitude earthquake, only slightly stronger than the actual 7.0 earthquake that eventually occurred. Unfortunately, 2 years is little time to prepare for such an event in a country like Haiti, which endures widespread poverty and lacks resources for preparedness and mitigation. A legacy of poor building standards has increased vulnerability and cannot be easily remedied.

Earthquake Hazards

Earthquakes produce many direct, and sometimes indirect, effects. Landslides, flooding, and tsunamis are considered secondary hazards and are discussed later in this chapter.

Typical Adverse Effects

Ground shaking can damage human settlements, buildings and infrastructure (particularly bridges), elevated roads, railways, water towers, water treatment facilities, utility lines, pipelines, electricity generating facilities, and transformer stations. Aftershocks can do great damage to already weakened structures. Significant secondary effects include fires, dam failures, and landslides, which may block waterways and cause flooding. Flooding may also be caused by seiches (back-and-forth wave action in bays) or by failures in dams and levees. Damage may occur to facilities that use or manufacture dangerous materials, resulting in chemical spills. Communications facilities may break down. Destruction of property may have a serious impact on shelter needs, economic production, and living standards of the affected community. Depending on their level of vulnerability, many people may be homeless in the aftermath of an earthquake.

The casualty rate is often high, especially when earthquakes occur in areas of high population density, particularly when streets between buildings are narrow, buildings are not earthquake resistant, the ground is sloping and unstable, or adobe or dry stone construction is used, with heavy upper floors and roofs.

Casualty rates may be high when quakes occur at night because the preliminary tremors are not felt during sleep and people are not tuned in to receive media warnings. In the daytime, people are particularly vulnerable in large unsafe structures such as schools and offices. Casualties generally decrease with distance from the epicenter. As a rule of thumb, quakes result in three times as many injured survivors as persons killed. The proportion of dead may be higher with major landslides and other secondary hazards. In areas where houses are of lightweight construction, especially with wood frames, casualties are generally much fewer, and earthquakes may occur regularly with no serious, direct effects on human populations.

The most widespread acute, serious medical problems are broken bones. Other health threats may occur with secondary flooding, when water supplies are disrupted (earthquakes can change levels in the water table) and contaminated water is used or water shortages exist, and when people are living in high-density relief camps, where epidemics may develop or food shortages exist.

In the aftermath of the Colombia earthquake of January 1999, which most heavily affected the city of Armenia, the death toll was 1185, and 160,000 people were left homeless, most in urban areas. In Armenia, where 60% to 70% of homes had been destroyed, movement was restricted by fallen debris and unemployment rose from 12% to 35%. People were living in unsatisfactory shelters made with plastic sheeting. Many migrated from the area to other places that could not absorb them. Although international response to aid Colombia was strong, the overwhelming need continued to pose problems. Five weeks after the earthquake, supplies of food, clean drinking water, and shelter materials were still urgently required. Hygiene and sanitation services and essential medicines were desperately needed. Social services were required to work toward normalizing the lives of victims, especially children. In Gujarat, India, where 30,000 people died in 2001, assistance agencies struggled for years to help rebuild the more than 300,000 houses that were lost. In the Kashmir earthquake of 2005, 3.3 million persons were left homeless in Pakistan, and many of them were at risk of dying from the winter cold and spread of disease.

The January 2010 Haiti earthquake affected an estimated 3 million people. It killed approximately 100,000 persons and injured approximately 300,000, although estimates of casualties widely vary. More than 1 million Haitians were left homeless. Vital infrastructure necessary to respond to the disaster, including air, sea, and land transport facilities and communication systems, was severely damaged or destroyed. Treatment of the injured was hampered by the lack of hospitals and morgue facilities; bodies were left to decay on the streets for many days. International assistance was offered in abundance, but the logistical capabilities in Haiti to receive emergency aid were limited. Doubtless, more lives were lost as a result of this vulnerability (Figures 89-4 and 89-5, online).

FIGURE 89-4 Nurse attending earthquake casualties in Haiti.

(Courtesy Pan America Health Organization.)

FIGURE 89-5 Makeshift hospital in Haiti.

(Courtesy Pan America Health Organization.)

Earthquake Risk Reduction Measures

Earthquake warning systems currently in use warn of an earthquake that has already occurred. Examples include those that notify the high-speed trains in Japan, which if derailed would cause hundreds of deaths. One minute before the 2011 Tohoku earthquake was felt in Tokyo, 1000 seismometers sent out warnings that saved many lives. In California, it is technically feasible to develop a system that could warn Los Angeles up to a minute before the arrival of the seismic waves, allowing certain preventive actions, such as taking cover, to occur. However, because predicting the location, time, and magnitude of earthquakes is still likely many years away, warning systems and earthquake prevention measures are currently not reliable alternatives to preparedness. Preparedness actions include the following:

FIGURE 89-6 Earthquake resistant lintels in Afghanistan.

(Courtesy Sheila B. Reed.)

Causal Phenomena and Characteristics

The geologic movements that cause a tsunami are produced in three major ways (Figure 89-7). The foremost cause is fault movement on the sea floor, accompanied by an earthquake. The second most common cause is a landslide occurring underwater or originating above the sea and then plunging into the water. The highest tsunamis ever reported were produced by a landslide at Lituya Bay, Alaska, in 1958. A massive rock slide produced a wave that reached a high water mark of 530 m (1740 feet) above the shoreline. A third cause of a tsunami is volcanic activity, which may uplift the flank of the volcano or cause an explosion.

FIGURE 89-7 Tsunamis are produced in three ways. A, Fault movement on the sea floor. B, Landslide. C, Submarine explosion from volcanic eruption.

Tsunamis differ from ordinary deep ocean waves, which are produced by wind blowing over water. Normal waves are rarely longer than 300 m (984 feet) from crest to crest. Tsunamis, however, may measure 150 km (90 miles) between successive wave crests. Tsunamis also travel much faster than ordinary waves. Compared with normal wave speed of around 100 km/hr (62 mph), tsunamis in the deep water of the ocean may travel at the speed of a jet airplane—800 km/hr (497 mph). Despite their speed, tsunamis increase the water height only 30 to 45 cm (12 to 18 inches) and often pass unnoticed beneath ships at sea. In 1946, a ship’s captain on a vessel lying offshore near Hilo, Hawaii, claimed he could feel no unusual waves beneath him, although he saw them crashing on the shore.

Contrary to popular belief, a tsunami is not a single giant wave. A tsunami can consist of 10 or more waves, termed a tsunami wave train. The waves follow each other in 5- to 90-minute intervals. As tsunamis approach the shore, they travel progressively slower. The final wave speed depends on the water depth. Waves in 18 m (59 feet) of water travel about 50 km/hr (31 mph). The shape of the near-shore sea floor influences how tsunami waves behave. Where the shore drops off quickly into deep water, the waves are smaller. Areas with long shallow shelves, such as the major Hawaiian Islands, allow formation of very high waves. In the bays and estuaries, seiches, in which the water sloshes back and forth, can amplify waves to some of the greatest heights ever observed.

On shore, the initial sign of a tsunami depends on what part of the wave first reaches land; a wave crest causes a rise in the water level, and a wave trough causes a recession. The rise may not be significant enough to be noticed by the general public. Observers are more likely to notice the withdrawal of water, which may leave fish floundering on the exposed sea floor. A tsunami does not always appear as a vertical wall of water, known as a bore, as typically portrayed in drawings. More often, the effect is that of an incoming tide that floods the land. Normal waves and swells may ride on top of the tsunami wave, or the tsunami may roll across relatively calm inland waters.

The flooding produced by a tsunami may vary greatly from place to place over a short distance, depending on submarine topography, shape of the shoreline, reflected waves, and modification of waves by seiches and tides. The Hilo, Hawaii, tsunami of 1946, originating in the Aleutian Trench, produced 18-m (59-foot) waves in one location and only one-half that height a few miles away. The sequence of the largest wave in the tsunami wave train also varies, and the destructiveness is not always predictable. In 1960 in Hilo, many people returned to their homes after two waves had passed, only to be swallowed up in a giant bore that, in this case, was the third wave.

Predictability

Tsunamis have occurred in all oceans and in the Mediterranean Sea, but the majority of them occur in the Pacific Ocean. The zones stretching from New Zealand through East Asia, the Aleutians, and the western coasts of the Americas all the way to the South Shetland Islands are characterized by deep ocean trenches, explosive volcanic islands, and dynamic mountain ranges.

Prior to 1946, the recorded effects of tsunamis included only local casualties and significant damage. The Tsunami Warning System (TWS) was developed in Hawaii shortly after the 1946 Hilo tsunami and is headquartered in the Pacific Warning Center in Honolulu. There are 26 member countries in the Pacific basin. The TWS works by monitoring seismic activity from a network of seismic stations. A tsunami is almost always generated by an undersea earthquake of magnitude 7 or greater. Therefore special warning alarms sound when a quake measuring 6.5 or more occurs anywhere near the Pacific. A tsunami watch is declared if the epicenter is close enough to the ocean to be of concern. Government and voluntary agencies are then alerted, and local media are activated to broadcast information. The five nearest tide stations monitor their gauges, and trained observers watch the waves. With positive indicators, a tsunami warning is issued.

The TWS met with general success in saving lives during the tsunamis of 1952 and 1957 in Hawaii. In 1960, however, two major earthquakes occurring a day apart rocked the coast of Chile in South America. The first registered 7.5 on the Richter scale and produced a small but noticeable wave in Hilo Bay. The second registered a stunning 8.5, more than 30 times the energy of the first, and authorities predicted generation of a large, destructive tsunami. When the waves hit Hilo, 15 hours after the earthquake, not all the public had taken the warnings seriously, and 61 people were killed. About 7 hours later the tsunami struck Japan, killing 180. By the time that information of conditions in Chile reached TWS, three giant waves had already destroyed villages along an 805-km (500-mile) stretch of coastal South America, arriving only 15 minutes after the earthquake.

Lack of an effective warning system has been blamed for the extensive loss of life from the tsunami generated in the Indian Ocean in December 2004. Over 290,000 are estimated to have died in 11 countries, and thousands more remain missing. Tsunamis have been relatively rare in the Indian Ocean, and the area has no international warning system. The first tsunami-generated wave crashed into Sumatra only 30 minutes after shaking from the earthquake had subsided. The tsunami ultimately traveled nearly 5000 km (3107 miles) to Africa. In contrast to stronger preparedness levels in the Pacific countries, citizens and tourists were not fully aware of the dangers and many watched from the beach with catastrophic results. In Kobe, Japan, the World Conference on Disaster Reduction in January of 2005 laid the groundwork for the first tsunami warning system in the Indian Ocean, much of which was positioned in recent years. Indonesia has set up costly and sophisticated tsunami warning systems and carried out numerous drills. However, 400 people were killed in an October 2010 tsunami on the Mentawai Islands, indicating that those most at risk are not able to receive warnings through communications systems or cannot flee from a tsunami generated close to shore.

Vulnerability

The following major factors contribute to vulnerability to tsunamis:

Typical Adverse Effects

The force of water in a bore, with pressures up to 10,000kg/m², can raze everything in its path. The flooding from a tsunami, however, affects human settlements most, by water damage to homes, businesses, roads, and infrastructure. Withdrawal of the tsunami also causes significant damage. As the water is dragged back toward the sea, bottom sediments are scoured out, collapsing piers and port facilities and sweeping out foundations of buildings. Entire beaches have disappeared, and houses have been carried out to sea. Water levels and currents may change unpredictably, and boats of all sizes may be swamped, sunk, or battered (Figures 89-8 to 89-10; Figures 89-8 and 89-10, online).

FIGURE 89-9 Boat perched on a house near Banda Aceh, Indonesia, following the December 2004 tsunami.

(Courtesy Sheila B. Reed.)

FIGURE 89-8 Ship washed ashore in tsunami, December 2004, in Koh Lanta, Thailand.

(Courtesy Sheila B. Reed.)

FIGURE 89-10 Generator ship washed ashore 2.3 miles inland, near Banda Aceh, Indonesia.

(Courtesy Sheila B. Reed.)

Casualties and Public Health

Deaths occur principally from drowning as water inundates homes or neighborhoods. Many people may be washed out to sea or crushed by the giant waves. Injuries occur from battering by debris. Little evidence exists of tsunami flooding directly causing large-scale health problems. Rapid effective assistance to the Banda Aceh (Indonesia) area in early 2005 prevented widespread outbreaks of disease in displacement camps (Figure 89-11). Malaria mosquitoes may increase because of water trapped in pools. Open wells and other groundwater may be contaminated by salt water and debris or sewage. Normal water supplies may be inaccessible for days because of broken water mains.

FIGURE 89-11 Displaced people in temporary settlements in Aceh Province, Indonesia.

(Courtesy Sheila B. Reed.)

Crops and Food Supplies

Flooding and damage by tsunami waves may result in the following:

1 Harvests may be lost, depending on time of year.

2 Land may be rendered infertile from saltwater incursion from the sea.

3 Food stocks not moved to high ground are damaged.

4 Animals not moved to high ground may perish.

5 Farm implements may be lost, hindering tillage.

6 Boats and fishing nets may be lost.

In July 1998, an earthquake of magnitude 7 occurred close to the northwest coast of Papua New Guinea. Although the tremor was felt over a large area, no earthquake damage was reported. Only 10 minutes after the quake, however, the first of three 7- to 10-m (23- to 33-foot) waves came ashore in Sandaun Province. The tsunamis struck at high speed after dark and penetrated up to 1 km (over half a mile) inland, totally destroying villages and vegetation along 50 km (31 miles) of the coast. Of the 9000 people affected, more than 2000 died, mainly as a result of being battered by debris as they were swept away by the water.

Tsunami Risk Reduction Measures

Strategies to reduce vulnerability to tsunamis include:

Causal Phenomena

The basic ingredients for a volcanic eruption are magma and an accumulation of gases beneath an active volcanic vent, which may be either on land or below the sea. Magma is composed of silicates containing dissolved gases and sometimes crystallized minerals in a liquid-like suspension. Driven by buoyancy and gas pressure, magma, which is lighter than surrounding rock, forces its way upward. As it reaches the surface, the pressures decrease, enabling the dissolved gases to effervesce, pushing the magma through the volcanic vent as the gases are released.

The chemical and physical composition of magma determines the amount of force with which a volcano erupts. Magmas that are less viscous allow gas to be released more easily. More viscous magma, perhaps containing a greater concentration of solid particles, may confine these gases longer, allowing greater pressures to build up. This greater pressure may lead to more violent eruptions.

Types

Volcanic eruptions may be described as follows in descending order of intensity (Figure 89-12).

FIGURE 89-12 Eruption types. A, Pelean. B, Plinean. C, Vesuvian. D, Vulcanian. E, Strombolian. F, Hawaiian. G, Icelandic.

(Modified from United Nations Development Program: Introduction to hazards, ed 3, Disaster Management Training Programme, UN Organization for Coordination of Humanitarian Assistance, New York, 1997.)

Characteristics

No international scale exists to measure the size of volcanic eruptions. The volcanic explosivity index (VEI) estimates the energy released in a volcanic eruption, based on measurements of the ejected matter, height of the eruption cloud, and other observations. The VEI scale ranges from 0 to 8. The largest eruption recorded was in Tambora, Indonesia in 1815, which had a VEI of 7.

The primary volcanic hazards are associated with products of the eruption: pyroclastic flows, air-fall tephra, lava flows, and volcanic gases. The most destructive secondary hazards include lahars, landslides, and tsunamis.

Location

The distribution of volcanoes, as with earthquakes, is determined by the location of geologic forces involving the tectonic or crustal plates. About 80% of the active volcanoes are located near subduction boundaries. Subduction volcanoes occur where denser crustal plates are shoved beneath less dense continental plates, which occurs in most of the Pacific Ocean, especially in the area along the rim, known as the Pacific Ring of Fire. Subduction volcanoes are found in the United States in the Cascade Range of the Pacific Northwest and further north in the Aleutian Islands off Alaska. The ring of subduction volcanoes continues along the Aleutian Trench to Japan, stretching south to the Philippines and Indonesia. Many volcanoes are located beneath the ocean, and submarine eruptions may cause tsunamis and other effects.

Rift volcanoes occur at divergent zones where two distinct plates are slowly being separated, in areas such as Iceland and East Africa; they account for about 15% of active volcanoes. Hot spot volcanoes are located where crustal weaknesses allow molten material to penetrate, but not necessarily on the plate boundaries. These isolated regions of volcanic activity exist in about 100 places in the world. The Hawaiian Islands, in the middle of the Pacific plate, and Yellowstone Park, within the North American plate, are good examples.

Predictability

Systematic surveillance of volcanoes, begun early in the 20th century at the Hawaiian Volcano Observatory, indicates that most eruptions are preceded by measurable geophysical and geochemical changes. Short-term forecasts of future volcanic activity in hours or months may be made through volcano monitoring techniques that include seismic monitoring, ground deformation studies, and observations and recordings of hydrothermal, geochemical, and geoelectric changes. By carefully monitoring these factors, scientists were able to issue a high confidence forecast of the 1991 Mt Pinatubo eruption, allowing a largely successful evacuation. The best basis for long-term forecasting (a year or longer) of a possible eruption is through geologic studies of the past history of each volcano. Each past eruption has left records in the form of lava beds. Deposits and layers of ash and tephra can be studied to determine the extent of the flows and length of time between eruptions.

Vulnerability

Rich volcanic soils and scenic terrains attract people to settle on the flanks of volcanoes. These people are more vulnerable if they live downwind from the volcano, in the path of historical channels for mudflows or lava flows, or close to waterways likely to flood because of silting. Structures with roof designs that do not resist ash accumulation are vulnerable even miles from a volcano. All combustible materials are at risk.

Typical Adverse Effects

Risk Reduction Measures

Strengthening forecasting, initiation or expansion of volcanic monitoring, creation of emergency response plans, and establishment of effective communications and warning systems are the most effective measures to reduce the risk from volcanic hazards. As the description in the next section indicates, people may not fully accept the validity warnings because of their own perception of the likelihood of hazards and adverse effects. Even those who accept the warnings may be willing to take risks to guard their livelihoods, homes, and possessions.

Causal Phenomena

Landslides result from sudden or gradual changes in the composition, structure, hydrology, or vegetation of a slope. These changes may be natural or caused by humans, and they disturb the equilibrium of the slope’s materials. A landslide occurs when the strength of the material in the slope is exceeded by the downslope stress. The resistance in a slope may be reduced by the following:

Downslope stress may be caused by the following:

Characteristics

Landslides usually occur as secondary effects of heavy storms, earthquakes, and volcanic eruptions. The materials that compose landslides are divided into two classes: bedrock and soil (Earth and organic matter debris). A landslide may be classified by its type of movement (Figure 89-13).

FIGURE 89-13 Landslides classified by type of movement. A, Fall. B, Slide. C, Topple. D, Lateral spread. E, Flow.

Predictability

The velocity of landslides varies from extremely slow (less than 0.06 m/year) to extremely fast (greater than 3 m/sec), which might imply a similar variation in predictability. In absolute terms, however, predicting the actual occurrence of a landslide is extremely difficult, although situations of high risk, such as forecasted heavy rainfall or seismic activity combined with landslide susceptibility, may lead to estimation of a time frame and possible consequences.

Estimation of landslide hazard potential includes historical information on the geology, geomorphology (study of landforms), hydrology, and vegetation of a specific area. Structural features that may affect stability include sequence and type of layering, lithologic changes, planes, joints, faults, and folds. The most important geomorphologic consideration in the prediction of landslides is the history of landslides in a given area.

The source, movement, amount of water, and water pressure must be studied. Climatic patterns combined with soil type may cause different types of landslides. For example, when monsoons occur in tropical regions, large debris slides of soils, rocks, and organic matter may occur. Plant cover on slopes may have either a positive or negative stabilizing effect. Roots may decrease water runoff and increase soil cohesion; conversely, they may widen fractures in rock surfaces and promote infiltration. In Nepal in 2002, a heavy monsoon season caused flooding and landslides, killing 500 people. The vulnerability to landslides was increased by the proximity of most communities to slopes and the poor quality of housing. A tragic slide in Santiago Atitlán, Guatemala, which partially buried its hospital and killed hundreds of people, on October 5, 2005 (Figure 89-14) was caused by torrential rains from Hurricane Stan combined with vulnerability of the location on the slopes of a volcano. If climate change predictions are accurate, landslides may be expected to increase in number. Along with more intense and extreme rainfall, the growth in population in many developing countries may increase landslide-related casualties.

FIGURE 89-14 Former hospital in Santiago Atitlán, Guatemala, buried during mudslide.

(Courtesy Paul S. Auerbach, MD.)

Vulnerability

Settlements built on steep slopes, in weak soils, on cliff tops, at the base of steep slopes, on alluvial outwash fans, or at the mouth of streams emerging from mountain valleys are all vulnerable. Roads and communication lines through mountainous areas are in danger. In most types of landslides, damage may occur to buildings even if foundations have been strengthened. Infrastructural elements, such as buried utility lines or brittle pipes, are vulnerable.

Typical Adverse Effects

Anything on top of or in the path of a landslide will be severely damaged or destroyed. In addition, rubble may damage lines of communication or block roadways. Waterways may be blocked, creating a flood risk. Casualties may not be widespread, except in the case of massive movements caused by major hazards such as earthquakes and volcanoes.

In addition to direct damage from a landslide, indirect effects include loss of productivity of agricultural or forest lands (if buried), reduced real estate values in high-risk areas and lost tax revenues from these devaluations, adverse effects on water quality in streams and irrigation facilities, and secondary physical effects, such as flooding.

Fatalities have resulted from slope failure in cases where population pressure has prompted settlement in areas vulnerable to landslides. Casualties may be caused by collapse of buildings or burial by landslide debris. Worldwide, approximately 600 deaths occur per year, mainly in the circum-Pacific region. The estimate for loss of life in the United States is 25 to 50 lives per year, greater than the average loss from earthquakes.

Risk Reduction Measures

Landslide management is a well-developed science in many countries. Landslides can be mitigated where sufficient resources are available. Basic reduction measures include terrain mapping, susceptibility analysis, stability analysis, and monitoring and warning systems. Warning systems include (a) sensors placed on a possible landslide path, (b) calculation of the stability of a slope and monitoring of the groundwater level, and (c) detection of early stages of landslide movement using sensors and inclinometers that generate detailed data sets. One major challenge is finding effective ways to manage landslides in developing countries. A further challenge centers on the fact that landslide risk mitigation may need to take into consideration changing environmental conditions, for example, looking more critically at areas underfilled with potentially degrading permafrost and the possibility of increased sediment loads and channel instability in rivers.

Causal Phenomena

The development cycle of tropical cyclones may be divided into three stages: formation and initial development, full maturity, and modification or decay. Depending on their tracks over the warm tropical seas and proximity to land, tropical cyclones may last from less than 24 hours to more than 3 weeks (the average duration is about 6 days). Their tracks are naturally erratic but initially move generally westward, then progressively poleward into higher latitudes, where they may make landfall, or into an easterly direction as they lose their cyclonic structure.

Formation and Initial Development Stage

Four atmospheric and oceanic conditions are necessary for development of a cyclonic storm (Figure 89-15):

1 A warm sea temperature (greater than 26° C [78.8° F] to a depth of 60 m [197 feet]) provides abundant water vapor in the air by evaporation.

2 High relative humidity (degree to which the air is saturated by water vapor) of the atmosphere to a height of about 7000 m (23,000 feet) facilitates condensation of water vapor into water droplets and clouds, releases heat energy, and induces a drop in barometric pressure.

3 Atmospheric instability (an above-average decrease of temperature with altitude) encourages considerable vertical cumulus cloud convection when condensation of rising air occurs.

4 A location of at least 4 to 5 latitude degrees from the equator allows the influence of the forces as the earth’s rotation (Coriolis effect) takes effect and induces cyclonic wind circulation around a low-pressure center.

FIGURE 89-15 Cyclone formation. A, Warm seas (>26° C [78.8° F]) cause rising humid air. B, Cooler high-altitude temperatures cause formation of cumulonimbus clouds. The surrounding air moves toward the central low-pressure area. C, Cumulonimbus clouds form into spiraling bands. The Coriolis effect causes winds to swirl around the central low-pressure area. D, High altitude dispels the top of the cyclonic air system. Dry high-altitude air flows down the “eye.” Hurricane force winds circle around the eye.

The atmosphere can usually organize itself into a tropical cyclone in 2 to 4 days. This process is characterized by increasing thunderstorms and rain squalls at sea. Meteorologists can monitor these processes with weather satellites and radar from as far as 645 m (400 miles) away from the storm. The existence of favorable conditions for cyclone development determines the cyclone season for each monitoring center. In the Indian and south Asian region the season is divided into two periods, from April to early June and from October to early December. In the Caribbean and United States, tropical storms and hurricanes reach their peak strengths in middle to late summer. In the Southern Hemisphere, the cyclone season extends from November to April or May, but occasionally cyclones occur in other months in lower latitudes.

Maturity Stage

As viewed by weather satellites and radar imagery, the main physical feature of a mature tropical cyclone is a spiral pattern of highly turbulent, giant cumulus thundercloud bands. These bands spiral inward and form a dense, highly active central cloud core that wraps around a relatively calm and cloud-free “eye.” The eye, where light winds occur, typically has a diameter of 20 to 60 km (12 to 37 miles) and appears as a black hole or dot surrounded by white clouds.

In contrast to the light wind conditions in the eye, the turbulent cloud formations extending outward from the eye accompany winds of up to 250 km/hr (155 mph), sufficient to destroy or severely damage most nonengineered structures in the affected communities. These strong winds are caused by a horizontal temperature gradient that exists between the warm core of the cyclone (up to 10° C [18° F] higher than the external environment) and the surrounding areas, resulting in a correspondingly high-pressure gradient.

Decay Stage

A tropical cyclone begins to weaken, in terms of its central low pressure, internal warm core, and extremely high winds, as soon as its sources of warm moist air begin to ebb or are abruptly cut off. This would occur during landfall, by movement into higher latitudes, or through influence of another low-pressure system. The weakening of a cyclone does not mean that danger to life and property is over. When the cyclone hits land, especially over mountainous or hilly terrain, widespread riverine and flash flooding may last for weeks. The energy from a weakening tropical cyclone may be reorganized into a less concentrated but more extensive storm system, causing widespread violent weather.

Characteristics

Tropical cyclones are characterized by their destructive winds, storm surges, and exceptional level of rainfall, which may cause flooding.

Deadly Hurricane Seasons

The 1998 Atlantic hurricane season, from June 1 to November 30, was one of the deadliest in 200 years, killing more than 10,000 people in eight countries and causing billions of dollars in damage. Fourteen named storms, four more than average, formed in the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. Of these, ten became hurricanes. Hurricane Georges followed a path across the U.S. Virgin Islands, Puerto Rico, the Dominican Republic, Haiti, and Cuba, killing more than 500 persons and causing $5 billion in damages. Hurricane Mitch moved across Central America, killing an estimated 10,000 persons in Honduras and wiping out the country’s infrastructure (Figure 89-16, online). Mitch regenerated as a tropical storm and then passed over south Florida.

FIGURE 89-16 Aftermath of hurricane Mitch in Honduras in 1998.

(Courtesy Paul Thompson, InterWorks.)

The 2005 Atlantic hurricane season, however, was the most active season on record, lasting into January 2006. Twenty-seven tropical storms formed, of which 15 became hurricanes. Of these, seven were major hurricanes, five becoming Category 4 and three reaching Category 5. Hurricane Wilma was the most intense ever recorded in the Atlantic. It caused at least 1918 deaths and record damages of over $100 billion. Hurricanes Dennis, Emily, Katrina, Rita, and Wilma struck Mexico, Cuba, and the United States (Florida, Alabama, Louisiana, Texas, and Mississippi). The most catastrophic effects of the season were felt in New Orleans, Louisiana, where hurricane Katrina caused a storm surge that breached levees and flooded most of the city. Katrina started as an extremely powerful Category 5 storm off the coast but weakened to Category 4 when it hit New Orleans. Because it dropped rapidly in intensity, New Orleans experienced significantly less wind damage than might have been expected from a Category 5 storm.

Predictability

Tropical cyclones form in all oceans of the world except the South Atlantic and South Pacific east of 140° W longitude. Nearly one-quarter form between 5° and 10° latitude of the equator and two-thirds between 10° and 20° latitude. It is rare for tropical cyclones to form south of 20° to 22° latitude in the Southern Hemisphere; however, they occasionally form as far north as 30° to 32° in the more extensive warmer water of the Northern Hemisphere. They are mainly confined to the warmer 6 months of the year but have occurred in every month of the year in the western North Pacific. Of concern is the influence that climate change might have on the frequency and severity of tropical cyclones by virtue of raising sea surface temperatures and contributing to rising sea levels. Warm sea surface temperatures influence cyclone development, and warmer ocean water will increase hurricane intensity.

The locations, frequencies, and intensities of tropical cyclones are well known from historical observations and, more recently, from routine satellite monitoring. Tropical cyclones do not follow the same track, except coincidentally over short distances. Some follow linear paths, others recurve in a symmetric manner, and still others accelerate or slow down and seem stationary for a time. For this reason, predicting when, where, and if a storm will hit land is often difficult, especially with islands. Typhoon Parma in the Philippines in 2009 made three consecutive landfalls in the same area, which experienced typhoon strength winds for 15 consecutive hours. In general, the difficulty in forecasting increases from lower to higher latitudes, whereas the margin of error in determining the cyclone center decreases as landfall approaches.

Special warning and preparedness strategies for evacuation from offshore facilities or closure of industrial plants must relate the costs and benefits of those strategies against the uncertainties of precision in the forecasts. For general community purposes that require a minimum 12 hours of preparedness time, the imprecision in forecasting the location of landfall within 24 hours should be generally tolerable, bearing in mind that highly adverse cyclonic weather usually commences about 6 hours before landfall of the cyclone. In the United States, a hurricane watch is issued when a hurricane is likely to strike within 36 hours, and a hurricane warning notifies of possible landfall within 24 hours. In September 2004, a Category 4 hurricane, Ivan, caused heavy damage to Jamaica, Grand Cayman, and the western tip of Cuba, and directly hit the Caribbean island of Grenada, home to 90,000 people. The island had not experienced a major hurricane in 40 years. Citizens received warnings in advance but generally did not have adequate preparedness measures in place. Remarkably few (39) died, but 90% of housing was damaged or destroyed (Figures 89-17 and 89-18; Figure 89-17, online).

FIGURE 89-18 A man standing on the site of his house in Jamaica, destroyed by hurricane Ivan, September 2004.

(Courtesy Sheila B. Reed.)

FIGURE 89-17 Damage in Grenada from hurricane Ivan, September 2004.

(Courtesy Sheila B. Reed.)

Regrettably, progress in reducing forecasting errors has remained slow in the last two decades despite huge investments in monitoring systems. However, substantial progress has been made in the organization of warning and dissemination systems, particularly through regional cooperation. The activities of national meteorologic services are coordinated at the international level by the WMO. Forecasts and warnings are prepared within the framework of the WMO’s World Weather Watch (WWW) program. Under this program, meteorologic observational data are provided nationally, and data from satellites and information provided by the regional centers are exchanged around the world. The WWW system includes 8500 land stations, 5500 merchant ships, aircraft, special ocean weather ships, automatic weather stations, and meteorologic satellites. A tropical cyclone is first identified and then followed from satellite pictures. A global telecommunications system relays the observations.

Ultimately, however, national services are responsible for providing forecasts and warnings to the local population regarding tropical cyclones and the associated winds, rains, and storm surges. Unfortunately, many of the less developed countries, where most deaths from tropical cyclones occur, do not possess state-of-the-art warning systems.

Vulnerability

Human settlements located in exposed, low-lying coastal areas are vulnerable to the direct effects of a cyclone, such as wind, rain, and storm surges. Settlements in adjacent areas are vulnerable to floods, mud slides, or landslides from the resultant heavy rains. The death rate is higher where communications systems are poor and warning systems are inadequate.

The quality of structures determines resistance to the effects of the cyclone. Those most vulnerable are lightweight structures with wood frames, older buildings with weakened walls, and houses made of unreinforced concrete block (Figure 89-19). Infrastructural elements particularly at risk are telephone and telegraph poles, fishing boats, and other maritime industries. Hospitals may be damaged, reducing access to health care and essential drugs.

FIGURE 89-19 How high winds damage buildings. A, Wind blowing into a building is slowed at the windward face, creating high pressure. The airflow separates as it spills around the building, creating low pressure or suction at the end walls, roof, and leeward walls. B, The roof may lift off and the walls blow out if the structure is not specially reinforced.

(Courtesy Disaster Management Center, University of Wisconsin.)

Typical Adverse Effects

Structures are damaged and destroyed by wind force, through collapse from pressure differentials, and by flooding, storm surge, and landslides. Severe damage can occur to overhead power lines, bridges, embankments, nonweatherproofed buildings, and roofs of most structures. Falling trees, wind-driven rain, and flying debris cause considerable damage.

Preparedness Measures Take Root after Cyclone Nargis in Burma

Cyclone Nargis, a Category 4 cyclone, struck Burma in May 2008, killing 145,000 and severely affecting 2.4 million people. Wind speeds reached 200 km/hr. Over 750,000 houses, 4000 schools, and 630 health facilities were destroyed or badly damaged. Over 60% of the total rice paddy fields were submerged; millions of livestock were killed; and stored food, seed stocks, boats, and equipment were destroyed. The cyclone, and the flooding that followed, damaged close to 13% of ponds used for drinking and household water in Yangon and up to 43% of ponds in Ayeyarwady Division. The damage caused by Cyclone Nargis was found to be on a scale nearly equivalent to that suffered by Aceh in Indonesia, one of the most affected areas hit by the 2004 Indian Ocean tsunami.

Recovery efforts in the 2 years following Cyclone Nargis helped to restore a large percentage of agricultural productivity in Burma, although rebuilding of houses (Figure 89-20, online) and infrastructure was notably slower due to insufficient resources to implement the national recovery plan. Extensive environmental damage from the cyclone was also weakly addressed. However, disaster risk reduction (DRR) measures were augmented by communities with the support of the government and assistance organizations. Many communities formed disaster management committees, promoted raising awareness, and developed evacuation plans for families and livestock (Figure 89-21, online). Committees and programs were established to replant mangroves and tree plantation barriers. Steps are being taken to strengthen hazard risk mapping, early warning systems, and scientific research to underpin national DRR policy.

FIGURE 89-20 Plastic sheeting repair to houses after Cyclone Nargis in Burma (Myanmar).

(Courtesy Sheila B. Reed.)

FIGURE 89-21 Women’s group for disaster risk reduction in Burma.

(Courtesy Sheila B. Reed.)

Risk Reduction Measures

The primary ways to reduce property damage from cyclones are accurate forecasting, sufficient warning, and establishment of evacuation procedures and building codes. As described earlier, significant challenges exist in forecasting the behavior of cyclones and other severe wind storms. Another major challenge is altering the perception of people who live in coastal areas regarding the danger from cyclonic activity. People may ignore the dangers for various reasons: lack of experience in hurricanes and cyclones, insufficient understanding of the hazard, repeated false alarms, or incorrect landfall predictions that breed complacency.

Causal Phenomena

Tornadoes and other severe local storms result from intense, local atmospheric instability, usually caused by solar heating of the earth’s surface, which causes intense convective columns. A tornado is a vortex in which air spirals inward and upward. It is frequently, but not always, visible as a funnel cloud hanging part or all of the way from the generating storm to the ground. The upper portion of the funnel consists of water droplets, and the lower portion usually consists of dust and soil being sucked up from the ground. The funnel size may range from a few meters to a few hundred meters in diameter and from 10 meters (33 feet) to several kilometers high. The funnel may undergo changes in appearance during the tornado’s lifetime. There may be a single well-defined funnel, multiple funnels, or funnels that appear to consist of several ropelike strands. Tornadoes may be as loud as the roar of a freight train. For a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. Scientists have not yet created a complete definition of the word; for example, there is disagreement about whether separate touchdowns of the same funnel constitute separate tornadoes.

Tornadoes are the most violent event associated with thunderstorms. They have been observed on every continent except Antarctica but are most frequent and fierce in the United States. As many as 1000 tornadoes may strike the United States each year, mostly in the central plains and southeastern states, although they have occurred in every state, mostly in the spring and summer. Of all the natural hazards in the United States, thunderstorms with associated winds, rain, hail, and lightning rank first in number of deaths, second in number of injuries, and third in property damage.

The most common type of tornado is small and lasts only a minute or two, causing minor damage over a track often less than 90 m (300 feet) wide and 1.6 to 3.2 m (1 to 2 miles) long. Most tornado-related deaths, injuries, and property damage are caused by relatively infrequent, large, and long-lasting tornadoes with paths more than 1 mile wide and more than 100 miles long over several hours. There are several different scales for rating the strength of tornadoes. The Fujita (F) scale rates tornadoes by damage caused, but this has been replaced in some countries by the updated Enhanced Fujita (EF) scale. An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers. The similar TORRO (T) scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.

Predictability

Although conditions favorable to tornado formation can often be predicted a number of hours in advance, the areas in which these conditions are found may cover hundreds of thousands of square miles. It is impossible to predict where individual tornadoes will occur. When a warning is issued, a tornado has already formed, and the threatened population may have only a few minutes to take cover. In the United States, when tornadoes are considered likely within a well-defined region, a tornado watch is issued. When a tornado is actually detected, either visually or on radar, a tornado warning is issued. The U.S. National Weather Service (NWS) has trained more than 230,000 trained Skywarn weather spotters across the U.S.; Canada has a similar program. When severe weather is anticipated, local weather service offices request that these spotters look out for severe weather and report any tornadoes immediately, so that the office can warn of the hazard. Storm spotters are needed because radar systems such as NEXRAD do not detect tornadoes. The radar systems merely detect “signatures” that hint at the presence of tornadoes. Radar may give a warning before there is any visual evidence of a tornado or imminent tornado, but ground truth from an observer can either verify the threat or determine that a tornado is not imminent. The spotter’s ability to see what cannot be detected by radar is especially important as distance from the radar site increases, because the radar beam becomes progressively higher in altitude further away from the radar, chiefly a result of the earth’s curvature, and the beam also spreads out.

Vulnerability

Most injuries from tornadoes are caused by flying or falling debris, usually from destroyed structures. The quality of structures will determine resistance to the effects of the tornado. Those most vulnerable are lightweight structures with wood frames, older buildings with weakened walls, mobile homes, and houses made of unreinforced concrete blocks. Thorough education regarding taking shelter from flying debris is essential to reduce deaths and injuries. Public education regarding the hazard is important to dispel myths. For example, opening house windows has not been shown to reduce damage even though this is a widespread belief; taking shelter under highway overpasses is not a safe way to wait out a tornado, contrary to some beliefs. On the other hand, taking shelter in a basement, under a staircase, or under a sturdy piece of furniture has been shown to increase chances of survival. Tornadoes have been known to cross major rivers, ascend mountains, affect valleys, and damage city centers. As a general rule, no area is safe from tornadoes, though some areas are less susceptible than others.

Examples of Tornado Outbreaks

The most extreme tornado in recorded history was the Tri-State Tornado, which roared through parts of Missouri, Illinois, and Indiana on March 18, 1925. It was likely an F5, although tornadoes were not ranked on any scale during that era. It holds records for longest path length (352 km [219 miles]), longest duration (about 3.5 hours), and fastest forward speed (117 km/hr [73 mph]) for a significant tornado anywhere on Earth. In addition, it is the deadliest (695 persons killed) single tornado in U.S. history. The deadliest tornado in world history was the Daultipur-Salturia Tornado in Bangladesh on April 26, 1989, which killed approximately 1300 people. Bangladesh has had at least 19 tornadoes in its history kill more than 100 people, almost one-half of the total deaths in the rest of the world.

The most extensive tornado outbreak on record was the Super Outbreak, on April 3 and 4, 1974, when 147 tornadoes struck Illinois, Indiana, Michigan, Ohio, West Virginia, Virginia, Kentucky, Tennessee, North Carolina, South Carolina, Georgia, and Alabama, killing 335 people, injuring more than 5500, affecting more than 27,000 households, and causing more than $600 million in damage. More than one-half the deaths were caused by fewer than 5% of the tornadoes. The worst of these struck Xenia, Ohio. It cut a swath of destruction one-half a mile wide and 16 miles long, killed 34 people, injured 1150, and damaged or destroyed 2400 homes.

The year 2008 overtook the year 1998 as the deadliest tornado season in the United States with 2192 tornadoes reported, 1691 confirmed (the most being in Kansas at 187) and 125 associated fatalities. Nine other tornado-related fatalities were reported elsewhere in the world: three in France, two each in Bangladesh and Poland, and one each in Russia and China. After a long lull in activity, a series of intense storms and associated cold fronts tracked across the Midwest, starting late on December 30, with most of the activity on December 31, New Year’s Eve, 2010. Early that morning, an EF3 tornado touched down in Washington County, Arkansas, destroying houses and killing at least four people. In nearby Benton County, Arkansas, another tornado caused significant damaged and injuries.

Risk Reduction Measures

The main means to prevent damage and casualties from tornadoes remains forecasting and warning to urge the public to take protective measures. Scientists still do not know the exact mechanisms by which most tornadoes form, and occasional tornadoes still strike without a tornado warning being issued. More research is needed to refine existing knowledge. In the United States, many universities and government agencies, such as the National Severe Storms Laboratory, private-sector meteorologists, and the National Center for Atmospheric Research, are actively seeking answers using various sources of funding, both private and public.

Pakistan Flood Disaster of 2010

In 2010, from mid-July until mid-August, all four of Pakistan’s provinces (Balochistan, Khyber Pakhtunkhwa, Punjab, and Sindh), as well as the Azad Jammu and Kashmir Region of Pakistan, flooded during the monsoon rains when dams, rivers, and lakes overflowed, killing at least 1750 people, injuring 2500, and affecting 23 million. The flood is considered the worst in Pakistan’s history, and the number of individuals affected by the flooding exceeds the combined total of those affected by the 2004 Indian Ocean tsunami, the 2005 Kashmir earthquake, and the 2010 Haiti earthquake. The flooding eventually affected about one-fifth of the country (nearly 62,000 square miles, an area larger than England) and formed what was called by some the largest fresh water lake in the world. Six weeks after the floods began, as rivers continued to devour villages and farmland in the southern province of Sindh, losses of crops, seed for the next planting season, and livelihoods were predicted. The UN Relief Web reported in January 2011 that millions of flood-affected people had still not received food and medicines, primarily due to inadequate relief resources and some villages being cut off from assistance by the flood waters.

Causal Phenomena

The most important cause of floods is excessive rainfall. Rain may be seasonal and occur over wide areas, or may form localized storms that produce the highest intensity rainfall. Some storms are attributed to atmospheric and oceanic processes, such as the El Niño Southern Oscillation (ENSO) or strong jet streams. Melting snow is another major contributor.

Types

Flash

Flash floods are usually defined as floods that occur within 6 hours of the beginning of heavy rainfall. This type of flooding requires rapid localized warnings and immediate response by affected communities if damage is to be mitigated. Flash floods are normally a result of runoff from a torrential downpour, particularly if the catchment slope is unable to absorb and hold a significant part of the water. Other causes of flash floods include dam failure or sudden breakup of ice jams or other river obstructions. Flash floods are potential threats, particularly where the terrain is steep, surface runoff is high, water flows through narrow canyons, and severe rainstorms are likely.

River

River floods are usually caused by precipitation over large catchment areas, by melting of the winter accumulation of snow, or sometimes by both. The floods take place in river systems with tributaries that may drain large geographic areas and encompass many independent river basins. In contrast to flash floods, river floods normally build up slowly, are often seasonal, and may continue for days or weeks. Factors governing the amount of flooding include ground conditions (the amount of moisture in the soil, vegetation cover, depth of snow, cover by impervious urban surfaces such as concrete), and size of the catchment basin (Figure 89-22).

FIGURE 89-22 Flooding and its causes.

(Courtesy Disaster Management Center, University of Wisconsin.)

Coastal

Some flooding is associated with tropical cyclones (also called hurricanes and typhoons). Catastrophic flooding from rainwater is often aggravated by wind-induced storm surges along the coast. Salt water may flood the land by one or a combination of effects from high tides, storm surges, or tsunamis. As in river floods, intense rain falling over a large geographic area will produce extreme flooding in coastal river basins.

Contribution by Humans

Floods are naturally occurring hazards but can become disasters when they affect human settlements. The magnitude and frequency of flooding often increase because of human actions. Settlement on floodplains contributes to flooding disasters by endangering humans and their assets. However, the economic benefits of living on the floodplain outweigh the dangers for some societies. Population pressure is now so great that people have accepted the risk associated with floods because of the greater need for a place to live. In the United States, billions of dollars have been spent on flood protection programs since 1936. Despite this, the annual flood hazard has become greater because people have built on floodplains faster than engineers can design better flood protection. The Mississippi River, which had been protected by 5600 miles of levees, flooded in 1993, affecting nine states. Some 70% of levees failed to protect against the record rainfall.

Urbanization contributes to urban flooding. Roads and buildings prevent infiltration of water, so runoff forms artificial streams. The network of drains in urban areas may deliver water and fill natural channels more rapidly than natural drainage routes, or drains may be insufficient and overflow. Natural or artificial channels may become constricted by debris or obstructed by river facilities, impeding drainage and overflowing the catchment areas. Failure to maintain or manage drainage systems, dams, and levees in vulnerable areas also contributes to flooding. Central Europe experienced severe flooding in 2002 and incurred $18 billion in damages, with the cities of Dresden and Prague particularly affected.

Deforestation and removal of root systems increase runoff. Subsequent erosion causes sedimentation in river channels, which decreases their capacity.

Predictability

Riverine flood forecasting estimates river level stage, discharge, time of occurrence, and duration of flooding, especially of peak discharge at specific points along river systems. Flooding resulting from precipitation, snowmelt in the catchment system, or upstream flooding is predictable from 12 hours to as much as several weeks ahead of events. Forecasts issued to the public result from regular monitoring of the river heights and rainfall observations. Flash flood warnings, however, depend solely on meteorologic forecasts and knowledge of local geographic conditions. The very short lead time for development of flash floods does not permit useful monitoring of actual river levels for warning purposes.

Flood hazard mapping supports flood management plans, land use planning, emergency evacuation plans and increased public awareness. For comparison with previous flood events and conversion to warning information, assessment of the following elements should be included: flood frequency analysis, topographic mapping and height contouring around river systems with estimates of water-holding capacity of the catchment area, precipitation and snowmelt records, soil filtration capacity, and, if in a coastal area, tidal records, storm frequency, topography, coastal geography, and breakwater characteristics.

An effective means of monitoring floodplains is through remote sensing techniques. The images produced by satellites can be interpreted to map flooded and flood-prone areas. Other efforts to improve forecasting are being implemented by United Nations organizations, such as the WMO (using WWW), and the Global Data Processing System (GDPS). These systems are strategic when flood conditions exist across international boundaries. The great majority of river and flash flood forecasts, however, depend on observations made by national weather services for activation of flood alert warnings.

Vulnerability

As with other hazards, perceptions by the general public of the flood hazard have improved through usage of flood mapping and public awareness campaigns. People in flood prone areas in developing countries may assume high risks due to overcrowding and the need to use the land for livelihood purposes.

At notable risk in floodplain settlements are buildings made of Earth or with soluble mortar, buildings with shallow foundations, or buildings that are nonresistant to water force and inundation. Infrastructural elements at particular risk include utilities, such as sewer systems, power and water supplies, and machinery and electronics belonging to industry and communications. Of great concern are food stocks and standing crops, confined livestock, irreplaceable cultural artifacts, and fishing boats and other maritime industries.

Other factors affecting vulnerability are lack of adequate refuge sites above flood levels and accessible routes for reaching those sites. Also, lack of public information about escape routes and other appropriate response activities renders communities more vulnerable. Vietnam, which has 3444 km (2149 miles) of coastline and a complex and ancient system of sea dikes, is chronically vulnerable to floods. The government is promoting a strong institutional network to support citizens to “live with floods,” reducing their vulnerability and providing social safety nets to assist with recovery.

Typical Adverse Effects

Structures are damaged by receiving the force of impact of flood waters, floating away on rising waters, becoming inundated, collapsing because of undercutting by scouring or erosion, and being struck by waterborne debris.

Damage is likely to be much greater in valleys than in open, low-lying areas. Flash floods often sweep away everything in their path. In coastal areas, storm surges are destructive both on inward travel and on outward return to the sea. Mud, oil, and other pollutants carried by water are deposited and ruin crops and building contents. Saturation of soils may cause landslides or ground failure.

Risk Reduction Measures

The major means to addressing flooding is through prevention. However, people may be lureding to the floodplain with false hopes of avoiding floods. Most dams and channels are not strong enough to withstand the heaviest water pressures and if they break down, flooding can be catastrophic. Furthermore, as levees and other physical barriers age, they become more likely to fail. European countries employ a variety of means to reduce the flood risk, such as a series of reservoirs in France called Les Grands Lacs de Seine (or Great Lakes), which helps remove pressure from the Seine during floods (especially during the regular winter flooding), protection from sea flooding by a huge mechanical barrier across the Thames River in London, underground canals that drain part of the flow of the Adige river in Northern Italy, and a series of flood defenses in The Netherlands called the Delta Works, with the Oosterschelde dam as its crowning achievement.

Since flooding may be beneficial to environmental regeneration, the challenge is to allow this while also ensuring personal and economic safety. The concept of integrated flood management, developed by the WMO in 2004, embraces flood plain land use that does not have adverse environmental impacts. Aspects include (a) integrated flood control that considers social and ecologic processes, (b) prioritization of floodplain land use, (c) integration of local stakeholder concerns, (d) flexible approach to flood control, and (e) extensive continuous monitoring of flood control measures and flooding events.

Types

Causal Phenomena

The reasons for lack of rain are not well understood. Displacement of the normal path of the jet stream may steer rain-bearing storms elsewhere. Recent research has focused on teleconnection, or linkages to global interactions, between the atmosphere and the oceans. Sea surface temperature anomalies (SSTAs) influence heat and moisture, such that warm surface water may create air conditions favorable for cyclone formation. A large-scale SSTA is linked to ENSO events in the Pacific. These involve the periodic (every 2 to 7 years) invasion of warm surface waters into the normally colder waters off the coast of South America. Droughts of 1982 to 1983 in Africa, Australia, India, Brazil, and the United States coincided with a major El Niño.

Human causes of drought, which include land use practices that give rise to desertification, such as deforestation, overcultivation, overgrazing, and mismanagement of irrigation, are thought to result in greater persistence of drought. Traditional drought-coping systems in Africa, such as pastoralists’ use of seasonal grazing lands and farmers’ use of fallow periods, have been reduced because of population pressures and economic policies (see Desertification, later).

Droughts vary in terms of intensity, duration, and coverage. Droughts tend to be more severe in drier areas of the world because of low mean annual rainfall and longer duration of dry periods. In dry areas, drought builds up slowly over several years of poor rainfall. Dry conditions in the African Sahel over a 16-year period led to widespread famine in 1984 to 1985. The quarter-century of drought conditions in the Sahel was interrupted by heavy rains in 1994. The effect of drought on food security depends, among other factors, on the size of the area affected by drought, as well as the overall size of the country. Larger countries, such as India and Brazil, are rarely completely affected by drought, but smaller countries may be totally affected (Figure 89-23). Worldwide food availability may be adversely affected by drought in grain-exporting nations.

FIGURE 89-23 Victims of drought in Ethiopia.

(Courtesy United Nations.)

Severe droughts that plagued China during the spring of 2010 affected 10 regions of southwestern China, as well as parts of Southeast Asia, including Vietnam and Thailand. Resultant dust storms in March and April affected much of East Asia. This drought has been referred to as the worst in a century in southwestern China. The China Meteorological Administration recorded temperatures averaging 2° C warmer than normal over 6 months, and one-half the average precipitation for the past year across the region. The higher temperatures and drop in precipitation were unprecedented since at least the 1950s. The effects of El Niño were believed to have contributed to the drought, which may have been exacerbated by global warming and resulting climate change.

In Syria in 2009 and 2010, 300,000 families were driven to Damascus, Aleppo, and other cities in what constituted one of the largest internal displacements in the Middle East in recent years. Rainfall has averaged between 45% to 66% less than normal in three eastern provinces during the past two years; the country uses more water than it receives from rivers, and wells dug to make up the shortfall are depleting aquifers. East Africa, often affected by drought and food insecurity, now faces its worst drought in decades. The drought has affected the livelihoods of more than 12 million people. In Judy 2011, the United Nations officially declared a famine in two regions of conflict-affected south Somalia where thousands of people have died. This is the first time a famine has been declared in nearly 30 years.

Predictability

Modern meteorologic monitoring and telecommunications systems can prevent casualties from drought-induced food shortages. The slow onset of drought allows a warning time between the first indications, usually several months, and when the population will be affected. In 1987, satellite imagery and rainfall reports indicated areas within Ethiopia with below-normal moisture and allowed timely intervention to avert a major food shortage. Longer-term prediction requires analysis of a century of rainfall data, which do not exist for some parts of the world. The World Meteorological Organization has established a base in Niamey, Niger, to promote regional training on agricultural production and drought response. The UN International Strategy for Disaster Reduction has convened panels of experts to steer development of the integrated Drought Early Warning System (DEWS), which focuses on strengthening data networks and data sharing on drought indicators.

Most countries in sub-Saharan Africa have installed famine early warning systems after the 1980s drought. The UN Food and Agriculture Organization (FAO) Global Information and Early Warning System (GIEWS) and the USAID-sponsored Famine Early Warning System (FEWSNET) issue regular bulletins on rainfall, food production, and famine vulnerability. These systems rely on satellite remote sensing to detect reduction in vegetation. In addition to the unique vantage point and condensed view, remote sensing provides a permanent historical record. The National Oceanic and Atmospheric Administration (NOAA) satellites provide twice-daily coverage of the planet’s surface. These data are available at many receiving stations around the world. NOAA has developed crop-monitoring technology for large areas of the Sahel.

Vulnerability

Although drought is more likely in dry areas with limited rainfall, physical factors, such as the moisture retention of soil and timing of rains, influence the degree of crop loss. Dependency on rain-fed agriculture increases vulnerability. Farmers unable to adapt with repeated plantings may experience crop failure. Livestock-dependent populations without adequate grazing territory are also at risk. Farmers dependent on stored water resources or irrigation are more vulnerable to water shortages and may face competition for water.

Drought-related effects are more severe in countries with yearly food deficiencies and in largely subsistence-level farming and pastoralist systems. Food shortages have the greatest impact where malnutrition already exists. Most food shortage–related deaths occur in the semiarid countries of sub-Saharan Africa, whereas in more developed countries the consequences are largely economic. Adverse effects may be more serious where drought response has not been adequately planned and where assistance measures may be poorly targeted or ineffective. There are indications that incidences of drought may increase, although this remains controversial. In any case, it is certain that societal vulnerability to drought is on the rise in many parts of the world.

Typical Adverse Effects

The effects of drought can be grouped as economic, environmental, and social. Economic effects include losses in crops, dairy and livestock, timber, fisheries, national economic growth, and income for farmers and others. Decreased tourism, loss of hydroelectric power and increased energy costs, increased food prices, unemployment, and losses of revenue to governments are other economic effects. Environmental effects include fires and dust storms; damage to animals, fish, and plant species and habitat; wind and water erosion of soils; reduced water quality or altered salination; and reduced air quality from dust and pollutants. Social effects include food shortage (malnutrition, famine), loss of human life, conflict between water users, health problems from decreased water flow, decline in living conditions, increased poverty, social unrest, and population migration for employment.

Risk Reduction Measures

A number of drought mitigation activities focus on restoring or conserving water resources. These include cloud seeding to induce rainfall, desalination of sea water for irrigation or consumption, rainwater harvesting or collection and storage of rainwater from roofs or other suitable catchments, recycling water (such as wastewater that has been treated and purified for reuse), building canals or redirecting rivers in massive attempts at irrigation within drought-prone areas, and outdoor water use restriction.

As described earlier, drought monitoring is critical for forecasting and warning and can help to prevent human-made drought. For instance, analysis of water usage in Yemen revealed that the water table (underground water level) is put at grave risk by overuse to fertilize khat, the largest cash crop. Land use measures include carefully planned crop rotation to help minimize erosion and allow farmers to plant less water-dependent crops during drier years.

Causal Phenomena

Cold air and below-freezing temperatures in the clouds and near the ground are necessary to make snow and ice. Moisture is needed to form clouds and precipitation. The source of moisture may be air blowing across a body of water, such as a large lake or the ocean. Lift, or the required force needed to raise the moist air to form the clouds and cause precipitation, can occur when warm air collides with cold air and is forced to rise over the cold dome. The boundary between the warm and cold air is called a front. Lift might also occur from air flowing up a mountainside.

Predictability

Although winter storm patterns are known in most areas of the world, predicting the intensity and characteristics of winter storms is not an exact science. The effects of El Niño on the winter storm patterns of 1998 are still being debated. Typical U.S. storm patterns include the “Nor’easter,” which affects the mid-Atlantic coast to New England from low-pressure areas off the Carolina coast. Research is continuously underway to improve forecasting tools and techniques. For example, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma provides feedback for the National Weather Service, NASA, and the Department of Defense.

The capacities of most national weather services allow individuals and public services to prepare for winter storms. Winter storm watches and warnings and winter weather advisories are normally issued in most vulnerable areas.

Vulnerability

Lack of a preparedness plan by individuals and communities and lack of understanding of the effects of winter storms increase vulnerability. Failure to heed warnings, lack of communication facilities to receive warnings, and insufficient preparation to cope with the cold or possible isolation from heavy snow can lead to casualties. For example, a person stranded in a vehicle or home during a winter storm without a storm survival kit or without adequate heat, food, or water may become hypothermic or dehydrated. Lack of protection for infrastructure, utilities, and houses can result in damage, loss of service, and roof collapse from heavy snow. Downed trees may later cause forest fires. Motorists unaccustomed to driving in winter storms cause more accidents. People living in uninsulated or unheated buildings are at greater risk for hypothermia.

The 1998 Ice Storm

A storm of unprecedented impact began on January 5, 1998, and ultimately damaged about 18 million acres of rural and urban forests throughout Maine, New Hampshire, Vermont, upstate New York, and southeastern Canada. The storm severely impacted the dairy industry, maple sugar industry, small businesses, public facilities, and infrastructure. Power outages lasted for up to 23 days. Thousands of people required shelter for an extended period, and nine people died in the United States.

The causal factors of the storm were both natural and human-made. Population and urbanization had recently increased in the area. Cold surface temperatures were overrun by a warm moist tropical air mass, resulting in record rainfall of 5 to 15 cm (2 to 6 inches). Below-freezing temperatures caused the rain to freeze on contact, producing ice accumulations of more than 7 to 10 cm (3 to 4 inches). These factors were intensified by the long duration and significant scope of the storm, resulting in severe flooding and ice damage. Much of the damage could not be assessed until the spring thaw. As a result of the storm, the Federal Emergency Management Agency (FEMA) reviewed the mitigation measures in place and made new recommendations.

Causal Phenomena

Various parts of the environment are subjected to the effects of toxic (poisonous) chemicals produced in manufacturing, such as paint and metal production, and the burning of fossil fuels, such as gasoline, coal, and oil. Some of these chemicals are heavy metals, such as lead, which are essentially nondegradable. Other toxic compounds, such as pesticides, are purposely introduced into the environment. Toxic chemicals may accumulate and affect the quality of air and water. Other pollutants of importance are from biologic sources, such as human waste, soil sediments, and decaying organic matter.

Ozone Depletion

Ozone is a form of oxygen composed of three atoms of oxygen. Most atmospheric ozone is concentrated in the upper atmosphere, or stratosphere. The ozone layer is 13 to 40 km (8 to 25 miles) above the earth. Ozone screens out harmful wavelengths of ultraviolet radiation (UV-B) that originate from the sun, protecting life on Earth (see Chapter 14). Ultraviolet light is associated with increased nonmelanoma skin cancer, ocular cataracts, and deterioration of the retina and cornea. In addition, oceanic phytoplankton are reduced, with damage to fish larvae and young fish. Because fish provide 14% of the animal protein consumed worldwide (60% of that in Japan), the impact could be significant. A hole in the ozone layer has been detected over Antarctica. This hole appears seasonally and is roughly the size of the United States. Thinning of the ozone layer is caused by chlorofluorocarbons (CFCs), chemicals used in refrigeration, foam products, and aerosol propellants. The CFCs that damage the ozone layer may also contribute to global warming. Although they compose a fraction of greenhouse gases, they account for 20% of the warming trend caused by radioactive trapping potential (10,000 times greater than that of CO₂).

Climate Change and Global Warming

For the past several decades, the climate of the earth has been changing rapidly as a result of warming of the troposphere. Scientific evidence indicates that there has been a warming of the atmosphere in the last 30 years that has manifested in increase in sea surface temperature, widespread melting of snow, glaciers, ice sheets and permafrost, and a significant increase in the rate of sea level rise. Over the past 50 years, the average global temperature has increased at the fastest rate in recorded history; the 3 hottest years on record have occurred since 1998 and the 12 years between 1995 and 2006 have included 11 of the 12 warmest years on record. Put in perspective, the climate of the earth over the past 3.2 million years has fluctuated greatly, with glacial and warmer interglacial intervals and accompanying adjustment by ecosystems and living creatures. A present concern is whether the changes are occurring too rapidly to allow adjustments to take place.

One explanation for global warming is the greenhouse effect, which is used to describe the role of atmospheric gases (such as CO₂, methane, and water vapor) in trapping radiation that would otherwise leave the atmosphere. Without this canopy of gases and clouds, the temperature of the earth would be extremely cold. The atmospheric gases therefore behave similarly to a greenhouse.

Since the beginning of the Industrial Revolution in the late 18th century, CO₂ in the atmosphere has increased by almost 25%, mainly from combustion of coal, oil, natural gas, and gasoline. A strong scientific consensus states that buildup of greenhouse gases is warming the global atmosphere. Computer models used to examine the climatic effects of increasing CO₂ suggest that if it doubles, global temperatures would increase on average by 3° to 5° C (37.4° to 41.0° F).

Because burning of fossil fuels is the primary cause of global warming, developed countries are mainly at fault, and poorer countries are more likely to be the victims. However, scientists estimate that 20% of greenhouse gases (mainly CO₂) are generated by deforestation, a trend occurring at a devastating rate in developing countries, particularly in tropical rainforests. Trees play a vital role in recycling CO₂ by taking it in, transforming it chemically, storing the carbon, and releasing oxygen into the air. When trees are cut down, left to decay, or burned, they release stored carbon to the air as CO₂. Recently in Central Africa, virgin rainforests were found to have air pollution levels comparable to those in industrial areas. A major cause of this pollution is smoke from fires that rage for months across huge stretches of land. These fires are set to clear shrubs and trees for production of crops and grasses. The effects of acid rain (pollutants that are held in the clouds and fall back to Earth in rainwater) and air pollution in Europe, Canada, and the United States also contribute to increased CO₂.

Another greenhouse gas is methane. Methane is generated by bacteria as they break down organic matter. It is emitted largely by landfills, cattle, and fermenting rice paddies. The concentration of methane gas in the atmosphere has doubled in the past 200 years, mainly because of expanded animal husbandry and rice cultivation, more landfills, and leaking natural gas pipelines.

The single biggest factor in vulnerability to climate change is poverty. Climate change will most greatly affect poor communities across Africa, Asia and South America.

Characteristics and Typical Adverse Effects

Air Pollution

Pollution of the troposphere (lower atmosphere) is damaging to agricultural crops, forests, aquatic systems, buildings, and human health. Primary pollutants often react to form secondary pollutants (acidic compounds), a frequent cause of environmental damage. The following effects are possible:

1 Crop and vegetation damage by injury to plant tissue, increasing susceptibility to disease and drought

2 Decline in forests caused by leaf damage by acidic compounds, acidic soils, and stresses of multiple pollutants

3 Damage to aquatic ecosystems so that they no longer support life

4 Degradation of building materials, such as metal, stone, and brick

5 Adverse impact on human health by damage to respiratory tracts

Marine Pollution

Marine pollution has the following major effects:

1 Spread of pathogens from human wastes, including viruses and protozoa, that cause hepatitis, cholera, typhoid, and other infectious diseases

2 Release of nondegradable materials, such as plastics and netting, that may injure marine mammals

3 Oil pollution from oil spills

4 Spread of hazardous chemicals and radioactive substances into the marine ecosystem, where they may accumulate in seafood

Freshwater Pollution

Freshwater pollution results in the following adverse effects:

1 Untreated wastewater carrying viruses and bacteria from human feces into human drinking water, which can result in illness or even in infant mortality

2 Eutrophication, or decay of organic matter, which decreases oxygen levels in water, upsetting the balance of the aquatic ecosystem

3 Adverse health effects in persons drinking untreated water from tainted sources

4 Water acidification, which reduces water’s capacity to support aquatic life

5 Runoff sediment from eroded soil deposits in drainage basins, reducing basin capacity and exacerbating flooding

6 Salinization from irrigation, with harmful effects on downstream agriculture

7 Pesticides and fertilizer chemicals, which accumulate in water and affect tissues in living organisms

Global Warming

The impacts of global warming are still uncertain. Computer models are unable to make reliable predictions of regional changes. Theoretically, the changes could lead to increase in disasters, including those caused by drought, floods, tropical cyclones, and tornados. The following changes may occur.

Rise in Sea Level

Melting of the Arctic ice sheets and alpine glaciers could cause the seas to expand and sea levels to rise. Depending on the degree of global warming, the seas may rise 30 cm to 2 m (12 inches to 7 feet) by 2075, jeopardizing coastal settlements and marine ecosystems. A rise of 1 m (3.28 feet) in sea level could flood 15% of arable land in Egypt’s Nile Delta and would flood 12% of Bangladesh, displacing 11 million people. The tiny island of the Maldives, inhabited by 200,000, would be submerged (Figure 89-24).

FIGURE 89-24 Islands with diminishing shorelines in the Maldives.

(Courtesy Sheila B. Reed.)

Climate Change

Natural disasters such as super-hurricanes could become common. A temperature increase of a few degrees in tropical seas can intensify hurricane production. The warmer oceans may increase the El Niño phenomenon near the coast of Peru. ENSO inhibits phytoplankton growth, causes fish and shellfish to migrate or die, and forces higher forms of life (e.g., birds, humans) dependent on this sea life to migrate or die.

Other climatic changes could lead to warmer and drier conditions in middle latitudes, higher temperatures in semitropical and tropical areas, and higher rates of evaporation. Rainfall patterns may also change. The combined effects of increased CO₂ and climate changes may alter plant and animal productivity. Plants may grow faster and larger but may have reduced nutritive value.

Changes in Ecosystems

In warmer climates, grasslands, savannas, and deserts may expand, rendering them vulnerable to increased degradation through erosion and fire. Animal species that do not adapt to the temperature increases may have to relocate to survive, which would be difficult, given population pressures on land. Plant species unable to adapt would perish.

Public Health Impact

Global warming may affect mortality because of heat stress and may increase the incidence of respiratory diseases, allergies, and reproductive illnesses. Geographic ranges of vector-induced diseases (e.g., mosquito-borne malaria, yellow fever) and parasitic diseases might increase.

Measurement

Risk Reduction Measures

Saving the Black Sea

The Black Sea, named for the dark clouds and fierce storms that affect its shores each autumn, faces an even darker future. The residues of modern agriculture and industry now threaten its marine life and the air quality of its bordering countries of Bulgaria, Georgia, Romania, the Russian Federation, Turkey, and Ukraine. The Black Sea is particularly vulnerable to pollution, because it collects 10 times more water per square meter of surface area than any other sea or ocean. It is fed by several major rivers, which deposit many of the pollutants. The most important source is the Danube, which flows through eight highly industrialized countries, all using chemically intensive agricultural practices. Other threats to the sea include insufficiently treated sewage and inputs of harmful substances, such as oil and exotic species from sea vessels.

In addition, the Black Sea has natural pollutants—organic matter collected over thousands of years, now decaying and diminishing the supply of oxygen in the water. In the unique two-stratum structure of the sea, in which salt water from the Mediterranean forms the bottom layer and fresh water creates the top layer, toxic hydrogen sulfide from the decomposing matter remains on the bottom layer, where oxygen is not present. Construction of irrigation works and dams has reduced the flow of fresh water into the Black Sea, so the toxic layer that was previously 200 m (656 feet) below the surface has now risen to a depth of only 80 to 100 m (262 to 328 feet).

Further deterioration of the Black Sea, along with air pollution from industries around it, could be economically disastrous to the surrounding countries that depend on the Black Sea to draw tourists. In 1992, acting on the mandate of the six Black Sea countries, the Black Sea Commission ratified a Convention on the Protection of the Black Sea Against Pollution. A strategic action plan, developed in 2002, sets out measures to conduct environmental impact assessments and audits, promote environmentally sound technologies and public involvement in environmental decision making, and promote green tourism and sustainable livelihoods. Fortunately, pollution reduction and regulation efforts led to a partial recovery of the Black Sea ecosystem during the 1990s, and a European Union (EU) monitoring exercise, EROS21, revealed decreased nitrogen and phosphorus values, relative to the 1989 peak. Recently, scientists have noted signs of ecologic recovery, in part due to construction of new sewage treatment plants in Slovakia, Hungary, Romania, and Bulgaria in connection with membership in the EU.

Causal Phenomena

The principal causes for loss and degradation of forests are conversion to other land uses (mainly agriculture and grazing) and overexploitation of forest products (industrial wood, fuel wood).

Underlying the obvious causes are fundamental problems in development, such as the use of inefficient agricultural practices (e.g., overgrazing), insecure land tenure, rising unemployment, rapid population growth, and failure to regulate and preserve forest lands. Contributing factors are air pollution, storms, pests, and diseases. A significant contributing cause in the 1990s was the number of wildfires that occurred in the western United States, Ethiopia, the western Mediterranean, and Indonesia.

Characteristics

Trees play a vital role in regulating the earth’s atmosphere, ecosystems, and weather systems. They recycle CO₂, a gas now increasing in the atmosphere and thought to contribute to global warming. They release moisture to the air, thus contributing to rainfall and moderating local and global climate. Their roots trap nutrients, improve soil fertility, and trap pollutants, keeping these from the water supply. Trees provide habitats for species, engendering diversity. They nurture traditional cultures by giving shelter, wood, food, and medicinal products. These benefits are lost as trees are destroyed.

The root systems of vegetation help retain water in the soil, anchor the soil particles, and provide aeration to keep soil from compacting. When vegetation dies, the nutrients go back to the soil. When root systems are removed, soil becomes destabilized. Water tends to flow off the top of the soil instead of percolating in, and it carries valuable topsoil along with it. This soil eventually forms sediment in the drainage basins.

Deforestation poses the most immediate danger by its contribution to the following hazards:

Of all the hazards associated with deforestation, flooding may be the most serious. Usually, curative measures (e.g., dredging and dam building) rather than preventive measures are taken to solve flooding problems. As flooding worsens in developing countries, more attention is given to protection of watersheds. In India, flood damages between 1953 and 1978 averaged $250 million per year. Today, even more people live in flood-prone areas. Flood problems may not be lessened without reforestation of the increasingly denuded hills of northern India and Nepal.

Predictability

Measurement and monitoring of forested areas may be conducted through ground-level sampling and aerial or satellite surveys. Each method has drawbacks. Ground sampling is tedious and difficult to extrapolate, aerial surveys are expensive, and satellite imagery poses difficulty in distinguishing forest from other vegetation. Combinations of methods usually produce the best results. Vague definitions in the study of deforestation continue to make exact determinations and forecasting difficult. Three different prediction methods follow:

Typical Adverse Effects

The specific impacts of deforestation include:

Risk Reduction Measures

Various types of forest management, reforestation, and community participation can reduce deforestation. Most governments now recognize the vital importance of national forestry programs. Foresters help people meet their basic needs for forest products, and not always from the traditional forest or concentrated woodlot. Farmers who practice reforestation on their lands contribute effectively to the environment. Reforestation has become intrinsically interwoven with other government policies that affect the population. Forestry therefore should be considered an integral part of land use and natural resource planning sectors of government.

Forests should be viewed by governments as capital resources to be managed. Management of the system should discourage concessionaires who have been given rights to sell wood obtained from property belonging to the government or others from practices that are not sustainable. Good management encourages highly selective harvesting without undue waste of remaining trees, especially in tropical forests. Involvement of communities in forest management is now a significant feature of national forest policies throughout the world. Forest management policies must consider the need to protect forests in conflict areas and to avoid exacerbating conflict over forest resources. For any country to address its loss of forests and ensure that forests will yield economic benefits well into the future, the following steps must be taken:

Forest management must be considered in the broadest sense of land use planning to include solutions for people as well as for trees. Compromises between complete destruction of the forests and complete conservation might entail regulated clearing of forests for shifting cultivation, habitation, or hunting; voluntary and intentional protection of forests or individual species by designating areas for reserves or national parks; and enrichment of the forest with species from other places. The last option may be considered risky, because pests and other species-specific problems may accompany introduction of non-native species.

Many unresolved scientific issues in forest management remain. How can the ever-expanding areas of secondary vegetation and degraded soils be managed to be more productive for the local people? Because most primary forests have disappeared, what type of forest can be established that would be stable and productive and that would ensure the conservation of biologic diversity? What further types of basic ecologic research are needed to manage natural forests?

Causal Phenomena

Role of Climate

Vulnerability to desertification and the severity of its impact are partially governed by climatic conditions of an area. The lower and more uncertain the rainfall, the greater is the potential for desertification. Other influencing factors are seasonal patterns of rainfall and high temperatures that increase evaporation, land use, and the type of vegetation cover.

The world’s drylands, which are inhabited by more than 2 billion people, are found in two belts centered approximately on the Tropic of Cancer and the Tropic of Capricorn (23.5 degrees north and south of the equator, respectively) and cover one-third of the earth’s surface. More than 80% of the total area of drylands is found on three continents: Africa (37%), Asia (33%), and Australia (14%). The drylands can be further classified into hyperarid, arid, and semiarid zones, depending on the average amount of rainfall received per year. Other factors, such as temperature and soil conditions, must be considered when determining the dryness ratio.

Both natural and human-derived climatic changes may contribute to desertification. Natural effects, such as long-term climatic cycles and the basic earth-sun geometry, have resulted in drier conditions in the Sahara. Human influence is associated with the predicted global warming trend and local climatic changes, in which deforestation has reduced the moisture-holding capacity of soil and has decreased cloud formation. The result is less rainfall and higher temperatures.

Despite the common misperception that desertification is caused by the desert advancing itself, land degradation can occur at great distances from deserts. Desertification usually begins as a spot on the land where land abuse has been excessive; from that spot, land degradation can spread outward with continued abuse (Figure 89-25). Desertification does not cause drought but may result in greater persistence of or susceptibility to drought. Drought, on the other hand, contributes to desertification and increases the rate of degradation. When the rains return, however, well-managed lands recover from droughts with minimal adverse effects. Land abuse during periods of good rains and its continuation during periods of deficient rainfall contribute to desertification.

FIGURE 89-25 Comparison of healthy and desertified regions.

(Modified from United Nations Development Program, Introduction to hazards, ed 3, Disaster Management Training Programme, UN Organization for Coordination of Humanitarian Assistance, New York, 1997.)

Role of Land Use Management

Desertification can be caused by five main types of poor land use: overcultivation, cash cropping, overgrazing, deforestation, and poor irrigation practices.

Overcultivation

Overcultivation damages the structure of the soil or removes vegetation cover, leaving the soil vulnerable to erosion. Reasons for overcultivation include drought, increasing demand for food because of population growth, cropping on marginal range lands unsuitable for long-term production, land tenure restrictions confining sectors of the population to marginal lands, mechanized farming, and expansion of cash cropping.

Cash Cropping

Although a large part of agricultural production in developing countries fills subsistence needs, some cash crops are grown for foreign exchange. Unfortunately, a feature of most cash crops is their extreme demand for nutrients and optimum conditions. Degradation of land occurs directly through improper management of such crops and indirectly by displacing subsistence crops and pastoralism to marginal lands.

Overgrazing

Overgrazing is a major cause of desertification (range lands account for 90% of desertified lands) and occurs when too many animals are pastured. The number of cattle in Niger, for example, increased an estimated 450% between 1938 and 1961 and an additional 29% by 1970, when the majority were killed by starvation. Livestock density increases when herd sizes grow too large in wet years and cannot be sustained in dry years. Lucrative markets for meat, such as Nigeria and the Middle East, have resulted in cattle ranches, where concentrated activity threatens land, with poor returns for the investment.

Better veterinary care has decreased mortality rates. Deep wells increase availability of water, allowing larger, less mobile herds that congregate in the well area and degrade the vegetation and soil.

Deforestation

Land is cleared for agriculture, livestock, and fuel wood production. Deforestation is the first step toward desertification, removing vegetative barriers and exposing land to sun, wind, and rain. In Africa, demands for fuel wood and charcoal exert considerable stress on wood resources.

Poor Irrigation Management

The concept of using irrigation to ward off the threat of crop failure during drought has been promoted by many development agencies. Ironically, poor management of irrigation projects has been a cause of desertification. In some cases, productivity falls and soils become salinized, alkalized, or waterlogged. The major problem is usually inadequate drainage, and damage may be irreversible. A key example is the Greater Mussayeb irrigation project in Iraq, begun in 1953. By 1969, waterlogging was widespread, and two-thirds of the soil was saline. In 1970, a project to reclaim the salinized land was begun, however, because of technical and organizational limitations, the project was not successful. Egypt, Iraq, and Pakistan have lost more than 25% of their irrigated areas to salinization and waterlogging.

Role of Government Policy

Population growth and economic expansion also contribute to desertification. As populations grow, government and multilateral policies must promote increased food production through appropriate technologies that prevent soil degradation and erosion. Government policy should also address the causes of poverty, or disadvantaged peoples will place more stress on land to obtain needed resources. Some governments choose to expand cash crop cultivation to improve foreign currency holdings rather than promote food security for the poor, or they fail to resolve conflicts over scarce resources. Policies may mandate land uses that are difficult to enforce and that result in breakdown of customary land tenure or natural resource management institutions.

Characteristics

The two main characteristics of desertification, degradation of soil and degradation of vegetation, have the same result: reduction of productivity.

Predictability

Desertification is a direct socioeconomic threat to more than 200 million people and a less direct threat to 700 million, but data are still insufficient to quantify the extent of the problem and its progression. It leads to estimated losses in agricultural production of $42 billion. Databases are incomplete or do not exist for many countries. More information is needed on the characteristics and status of dryland ecosystems. An understanding of climatic changes, including the effects of possible global warming, is crucial to predictability. Socioeconomic indicators showing trends in human health, income, and welfare must be collected to understand related issues.

The International Soil Reference Centre and UNEP support the Global Assessment of Soil Degradation (GLASOD), which uses a geographical information system (GIS) to access data for different areas of the world and estimate land degradation.

Rate and Scope

Although the numbers remain controversial, yearly losses to desertification are estimated at 1.0 to 1.3 million hectares of irrigated land, 3.5 to 4.0 million hectares of rain-fed cropland, and 4.5 to 5.8 million hectares of range land. These estimates represent an increase of 3.4% from estimates in 1994, indicating that the situation is worsening. The area of desertification is thought to be increasing at about 60,000 square km per year. GLASOD estimates for extent of desertification between 1983 and 1990 were 20% of dryland soil.

Desertification affects drylands in more than 110 countries but is concentrated in Asia and Africa, which together account for 70% of all desertified land. Scientists have tried to quantify the areas desertified on a worldwide basis. The physical damage can be measured in reduced productivity of soils and loss of vegetation. The number of casualties cannot be scientifically extrapolated, but deaths occur, directly from famine or indirectly from reduced standards of living.

Risk Reduction

The Secretariat of the United Nations Convention to Combat Desertification (UNCCD), an organization with 193 countries as parties by 2009, works with governments to highlight national focal points to communicate with the scientific communities, civil society organizations, the public, and other stakeholders on matters related to desertification, land degradation, and drought. A number of innovative methods are in use to help mitigate desertification, but a great deal more effort and resources are required to stop the progression. Mitigation measures should be included in national action plans to address agricultural development, drought, deforestation, and loss of biodiversity, among others. Educating children in schools and community members about the desertification hazard and dangers of deforestation is critical, as are supporting planting of seedlings and promoting other local mitigation measures. Solutions to the need for cooking fuel include solar ovens and efficient wood-burning cook stoves, which have helped to relieve pressure on the environment; however, these may be too costly for the poor to afford unless subsidized.

Techniques to improve and rejuvenate soil include the use of seawater that is desalinated and pumped inland. Fixating the soil is often done through the use of shelter belts, woodlots, and windbreaks. A “Green Wall of China,” eventually intended to stretch more than 5700 km (3500 miles) in length (nearly as long as China’s Great Wall), is being planted in northeastern China to protect deserts created by human activity. Soil enrichment and restoration of its fertility are often accomplished by planting such foods as grains, barley, and dates, as well as legumes, which extract nitrogen from the air and fix it in the soil. Sand fences can also be used to control drifting of soil and sand erosion.