What is a drought?
A drought is defined as "a period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area." -Glossary of Meteorology (1959).
In easier to understand terms, a drought is a period of unusually persistant dry weather that persists long enough to cause serious problems such as crop damage and/or water supply shortages. The severity of the drought depends upon the degree of moisture deficiency, the duration, and the size of the affected area.
There are actually four different ways that drought can be defined.
• Meteorological - a measure of departure of precipitation from normal. Due to climatic differences, what might be considered a drought in one location of the country may not be a drought in another location.
• Agricultural - refers to a situation where the amount of moisture in the soil no longer meets the needs of a particular crop.
• Hydrological - occurs when surface and subsurface water supplies are below normal.
• Socioeconomic - refers to the situation that occurs when physical water shortages begin to affect people.
What are the impacts of a drought?
Lack of rainfall for an extended period of time can bring farmers and metropolitan areas to their knees. It does not take very long; in some locations of the country, a few rain-free weeks can spread panic and affect crops. Before long, we are told to stop washing our cars, cease watering the grass, and take other water conservation steps. In this situation, sunny weather is not always the best weather.
The Dust Bowl days of the 1930's affected 50,000,000 acres of land, rendering farmers helpless. In the 1950's, the Great Plains suffered a severe water shortage when several years went by with rainfall well below normal. Crop yields failed and the water supply fell. California suffered a severe drought around 1970. Rainfall was below normal for 1 1/2 years, and by the time September 1970 arrived, the fire potential was extremely high and dangerous. Temperatures rose to near the century mark and fires broke out. Losses were in the tens of millions of dollars.
The worst drought in 50 years affected at least 35 states during the long hot summer of 1988. In some areas the lack of rainfall dated back to 1984. In 1988, rainfall totals over the Midwest, Northern Plains, and the Rockies were 50-85% below normal. Crops and livestock died and some areas became desert. Forest fires began over the Northwest and by autumn, 4,100,000 acres had been burned. A government policy called "Let Burn" was in effect for Yellowstone National Park. The result? Half of the park--2,100,000 acres were charred when a huge forest fire developed.
How do meteorologists predict droughts?
Meteorologists determine the onset and the end of a drought by carefully monitoring meteorological and hydrological variables such as precipitation patterns, soil moisture, and stream flow. To do this, meteorologists make use of various indices that show deficits in precipitation over periods of time.
This and more information can be found at the National Oceanic and Atmospheric Administration Web site at www.noaa.gov