Droughts
Drought is an extended period of unusually dry weather when there is not enough rain. The lack of precipitation can cause a variety of problems for local communities, including damage to crops and a shortage of drinking water. These effects can lead to devastating economic and social disasters, such as famine, forced migration away from drought-stricken areas, and conflict over remaining resources.
Because the full effects of a drought can develop slowly over time, impacts can be underestimated. However, drought can have drastic and long-term effects on vegetation, animals, and people. Since 1900, more than 11 million people have died and more than 2 billion people have been affected by drought. Drought is also one of the costliest weather-related disasters. In the past 30 years, the U.S. has experienced 16 billion-dollar droughts, totaling $195 billion in losses.
Defining Drought (Chunk 1)
Drought is a complicated phenomenon, and can be hard to define. One difficulty is that drought means different things in different regions. "Drought" is not a set number or equation. It is defined depending on the average amount of precipitation an area is accustomed to receiving.
For example, in Atlanta, Georgia, the average rainfall is about 50 inches a year. If significantly less rain falls, there may be water shortages and a drought may be declared. However, arid regions, such as the deserts of the American Southwest, receive less than 3 inches of rainfall each year. A drought in Atlanta would be a very wet period in Phoenix, Arizona!
Determining the start of a drought can be tricky. Unlike many natural hazards that bring about sudden and dramatic results—such as earthquakes, tornadoes, and hurricanes—the onset of a drought can be gradual and subtle. It can take weeks, months, or even years for the full effects of long-term inadequate rainfall to become apparent.
The end of a drought can also be difficult to determine. While a single rainstorm will provide shortterm relief from a drought, it might take weeks or months before levels of precipitation return to normal. The start and end of a drought are often only clear in hindsight.
Causes of Drought (Chunk 2)
Most droughts occur when regular weather patterns are interrupted, causing disruption to the water cycle. Changes in atmospheric circulation patterns can cause storm tracks to be stalled for months or years, dramatically impacting the amount of precipitation a region normally receives and resulting in droughts or floods. Changes in wind patterns can also affect how much moisture a region can absorb.
Scientists have found a link between certain climate patterns and drought. El Niño is a weather event where the surface water in the Pacific Ocean along the central South American coast rises in temperature. These warmer waters alter storm patterns and are associated with droughts in Indonesia, Australia, and northeastern South America. El Nino events are not predictable and can occur every two to seven years.
La Niña is the counterpart to El Niño, when the surface water in the Pacific Ocean along the coast of South America decreases in temperature. The cooler waters affect storm patterns by contributing to drier-than-normal conditions in parts of North and South America. While El Niño usually lasts less than a year, La Niña can extend for one to three years. The effects of La Niña on weather patterns are often more complex than El Niño. Two of the most devastating droughts in the history of the United States—the 1930s Dust Bowl and the 1988 drought in the Midwest—are associated with the effects of La Niña.
Impacts of Drought (Chunk 3)
Trees and other plants have adapted to withstand the effects of drought through various survival methods. Some plants (such as grasses) will slow their growth or turn brown to conserve water. Trees can drop their leaves earlier in the season to prevent losing water through the leaf surface. However, if drought conditions persist, much vegetation will die.
Certain plants have adapted so they can withstand long periods without water. Yuccas, for instance, have deep root systems that can seek out water with incredible efficiency. Cacti have spiny, hairy leaves that limit how much water they lose to evaporation. Mosses can withstand complete dehydration. Juniper trees can self-prune by steering water only toward the branches they need to survive. Other plants only grow when there is enough water to support them. In periods of drought, their seeds can survive under the soil for years until conditions are favorable again.
However, many organisms cannot adapt to drought conditions, and the environmental effects of extended, unusual periods of low precipitation can be severe. Negative impacts include damage to habitats, loss of biodiversity, soil erosion, and an increased risk from wildfires. During the U.S. drought of 1988, rainfall in many states was 50 to 85 percent below normal. Summer thunderstorms 3 of 13 produced lightning without rain and ignited fires in dry trees. More than 4 million acres of forest in the Northwest burned in a single summer. In Yellowstone National Park alone, 36 percent of the park was destroyed by fire.
Drought can also create significant economic and social problems. The lack of rain can result in crop loss, a decrease in land prices, and unemployment due to declines in production. As water levels in rivers and lakes fall, water-supply problems can develop. These can bring about other social problems. Many of these problems are health-related, such as lack of water, poor nutrition, and famine. Other problems include conflicts over water usage and food, and forced migration away from drought-stricken areas.
While drought is a naturally occurring part of the weather cycle and cannot be prevented, human activity can influence the effects that drought has on a region. Many modern agricultural practices may make land more vulnerable to drought. While new irrigation techniques have increased the amount of land that can be used for farming, they have also increased farmers’ dependence on water.
Traditional farming techniques allow land to “rest” by rotating crops each season and alternating areas where livestock graze. Now, with many areas in the world struggling with overpopulation and a shortage of farmland, there is often not enough arable land to support these sustainable farming practices. Over-farming and overgrazing can lead to soil being compacted and unable to hold water. As the soil becomes drier, it is vulnerable to erosion. This process can lead to fertile land becoming desert-like, a process known as desertification. The desertification of the Sahel in North Africa is partly blamed on a prolonged drought whose effects were intensified by farming practices that result in overgrazing.
Increased drought conditions in Kenya have been attributed to deforestation and other human activities. Trees help bring precipitation into the ground and prevent soil erosion. But in 2009, it was reported that one-quarter of a protected forest reserve had been cleared for farming and logging, leading to drought conditions affecting 10 million people around the country.
Major Droughts in the Past Century (Chunk 4)
The Dust Bowl of the 1930s is probably the most well-known drought experienced by the U.S. By 1934, 80 percent of the U.S. was struggling with moderate-to-severe drought conditions. The drought lasted nearly a decade and had devastating effects on crop production in the Great Plains. The combination of lack of rain, high temperatures, and strong winds affected more than 50 million acres of land. Massive clouds of dust and sand formed as unusually strong winds lifted the dry soil into the air. These clouds could block out the sun for days, giving the period the name “dustbowl.” In 1934, one dust cloud infamously traveled 1,500 miles, from the Great Plains to the eastern U.S.
Mass migration was an indirect effect of the Dust Bowl. Farmers and their families were forced to migrate to other areas in search of work, and by 1940, 2.5 million people had fled the Great Plains. Of those, 200,000 moved to California. The influx of migrants into existing economies already strained by the Great Depression led to a rise in conflict, unemployment, and poverty.
In the late 1980s, the U.S. experienced the costliest drought in its history. The three-year spell of high temperatures and low rainfall ruined roughly $15 billion of crops in the Corn Belt. The total of all the losses in energy, water, ecosystems, and agriculture is estimated at $39 billion. Federal assistance programs were able to help many farmers, but a longer-lasting drought would make it more difficult for the government to provide nationwide aid.
Australia is also a frequent victim of drought. The last decade has been especially severe, earning it the name The Big Dry or The Millennium Drought. Much of the country was placed under water restrictions, wildfires spread in the dry weather, and the water level in some dams fell to 25 percent. In 2007, 65 percent of viable land in Australia was declared to be in a drought. The drought was officially declared over in April 2012.
Preparing for Drought (Chunk5)
People and governments need to adopt new practices and policies to prepare as much as possible for inevitable future droughts. Emergency spending once a crisis has begun is less effective than money spent in preparation. The Federal Emergency Management Agency (FEMA) estimates that every $1 spent in planning for a natural hazard will save $4 in the long term.
Many areas are extremely vulnerable to drought as people continue to be dependent on a steady supply of water. The U.S. Department of Agriculture recommends a series of conservation practices to help farmers prepare for drought. Some preventative measures include installing an efficient irrigation system that reduces the amount of water lost to evaporation, storing water in ditches along fields, regularly monitoring soil moisture, planting crops that are more drought-resistant, and rotating crops to allow water in the soil to increase.
In urban areas, many cities are promoting water conservation by addressing water usage habits. Some enforce water restrictions, such as banning car-washing at home, limiting days when lawns and plants can be watered, and offering rebates and assistance programs to fix household leaks.
Some drought-ravaged cities are taking even more extreme measures to prepare for future droughts. In Australia, the city of Perth is planning to start a massive wastewater-recycling program in 2016 that will eventually provide one-quarter of the city’s water demands.