Drought
Of all natural disasters, drought is the most subtle. Often, farmers cannot tell there is going to be a drought until it is too late. Unlike flash floods, drought is slow to develop. Unlike earthquakes, with destruction to the exterior environment, drought does its damage underground long before dust storms rage across the plains.
Technically, drought is measured by the decrease in the amount of subsoil moisture that causes crops to die or yield less (agricultural drought) or by a drop in the water level in surface reservoirs and below ground aquifers, causing wells to go dry (hydrological drought). Agricultural plus hydrological drought can lead to sociological drought. In this condition, drought effects food and water supplies to the extent that people have to rely on relief donations or are forced to migrate to another area.
Droughts are worldwide, repetitive, and unpredictable. Scientists believe there is a drought somewhere on the earth at any time. Nor are droughts recent developments; analysis of rock cores, glacial ice cores, and tree rings reveal prehistorical and historical droughts, some of which lasted for several decades. Tree rings in California, for example, record a 40-year-drought 300 years ago.
The direct cause of drought is a continued decrease in optimal rainfall. But what causes clouds not to form over an area, or the winds to carry rain-bearing clouds elsewhere, is complex. Climate change will alter the location of increased and reduced rainfall, so that some places that have always been well-watered will experience drought.
Some scientists believe that El Niño-La Niña events in the western Pacific Ocean are main drivers in the cause of droughts around the world. El Niño, an eastward flow of warm surface waters, creates a high pressure zone over the equator that results in a change in the high and low pressure zones in other parts of the world. This affects the flow of the jet stream and results in a disturbed rainfall pattern, causing, for example, excessive rain in California and drought in southwestern Africa, among other places. The La Niña, which usually follows El Niño, is an upwelling of cold deep waters in the western Pacific Ocean. It causes disturbed pressure zones that result in droughts in the Midwest, among other places.
Drought prediction is still in its infancy. Although scientists know that El Niño-La Niña events cause droughts in specific areas, they cannot yet predict when El Niño will occur. Weather satellites can measure subsoil moisture, a good indicator of incipient drought, but other factors also contribute to drought.
Lack of rain, for example, in the Sahel, is exacerbated by man-made environmental problems, such as cutting down trees for fuel and not allowing the soil to lie fallow, which conserves soil moisture. Overgrazing by animals such as cattle, goats, and sheep also contributes to the denuding of topsoil, which blows away in the wind, a condition known as desertification. Drought then becomes a cycle that feeds on itself: lack of trees reduces the amount of water vapor given off into the atmosphere; lack of topsoil reduces water retention. The result is that local rainfall is reduced, and the rain that does fall runs off and is not absorbed. Lack of rain has been the reason for five years of consecutive drought in Texas. The total amount of profit loss from 1998 until 2002 is estimated at $3.7 billion dollars.
Of all the water on the earth, less than 3% is fresh water. A lot of water is lost in evaporation, especially in arid climates, not only during rainfall but when it is stored in surface reservoirs. Rainwater or snowmelt that seeps into below-ground permeable rock channels, or aquifers, is pumped into wells in many communities. High-tech pumps have contributed to an increased drain on aquifers; if an aquifer is pumped too quickly, it collapses, and the ground above sinks. To increase water bank supplies, some communities recharge their aquifers by pumping water into them when they are low.
The only new water introduced into the hydrologic cycle is purified ocean water. Desalinization plants are expensive to build and maintain and often require burning fossil fuels or wood to run. Future plans include perfecting retrieving solar energy and wind energy.
Currently, farm irrigation uses most of the world's fresh water supply, but as city populations grow, they are expected to become the biggest consumers, and urban conservation measures will become imperative. Some communities already recycle wastewater for small farms and domestic garden use. Drought-causing industrial pollutants that "freeze" the water supply by rendering it toxic are being reduced and resolved under federal law. Reduced or low-flow shower heads and toilets are required in new construction in some states.
Distributing water from more to less abundant supplies by laying pipes and installing pumps within a state or a country requires money and management. If water is fed across state or international boundaries, legal and political negotiations are necessary.
During severe drought, sociologists find that people must either adapt, migrate, or die. Death, however, is usually caused by other factors such as war or poverty, as in the Sahel, where relief food supplies have been hijacked and sold at high prices, or where people in remote villages must walk to the distribution centers.
Some migrations have been permanent, as in the migration to California during the Midwestern Dust Bowl in the 1930s. Others are temporary, as in the Sahel region, where people migrate in search of food and water, crossing country lines.
Most people adapt in drought by making the most of their resources, such as building reservoirs or desalination plants or laying pipes connecting to more abundant water supplies. Farmers often invest in high-tech irrigation techniques or alter their crops to grow low-water plants, such as garbanzo beans.
Drought has also been the inspiration for inventions. The American West at the turn of the twentieth century gave rise to numerous rainmakers who used mysterious chemicals or noisemakers to attract rain. Most inventions failed or were unreliable, but out of the impetus to make rain grew silver iodide cloud-seeding, which now effects a 10–15% increase in local rainfall in some parts of the world.
Resources
Books
Glantz, M. H., ed. Drought and Hunger in Africa: Denying Famine a Future. New York: Cambridge University Press, 1987.
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