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Drought: Slow and Deadly
By Paul Hoversten
Washington Bureau Chief
posted: 08:34 am ET
01 April 2000
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drought_sidebar_000331 WASHINGTON -- Scientists call drought a "creeping disaster" because, unlike a flood or hurricane, it arrives slowly and spreads gradually. But its effects can be enormous. The costliest natural disaster in U.S. history was the drought of 1988, which caused an estimated $40 billion, largely in lost crops and livestock. That's costlier than Hurricane Andrew or the great Mississippi floods of 1993. According to the National Weather Service, drought is a normal part of virtually every climate on Earth and it can result from both natural events, such as a long dry spell, or human activities that increase the demand for water.No one has been able to produce an objective, universally accepted definition of drought. That's because every locale has its own working definition. In Lubbock, Texas, for example, 20 inches (50 centimeters) of rain a year would be considered slightly wetter than normal. In Nashville, Tennessee it would be a severe drought. Scientists look at three main types of drought. - Meteorological drought, which is usually based on long-term, abnormal rainfall or snowfall.
- Hydrological drought, which refers to low levels in groundwater supplies and water beneath the ground. It is measured in low flows in streams and rivers and low levels in lakes, reservoirs and groundwater levels.
- Agricultural drought, which occurs when there isn't enough moisture in the soil for crops to grow. This type of drought usually comes after a meteorological drought but before a hydrological drought.
To determine when an area is in a drought, scientists use a complex index that factors in rainfall, temperature, snowpack, stream flow and other water supply indicators. The index has been calculated for every part of the country for more than 100 years.
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