As defined by the NOAA Weather Service, drought is defined is “a period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area.” More simply, a drought is a period of unusually persistent dry weather lasting 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.
Short term effects of drought include excessively dry soil causing plants stress and crop failure. When rainfall is less than normal for several weeks, months, or years; the following may occur: the flow of streams and rivers declines; water levels in lakes and reservoirs fall; the water table drops, i.e. the depth to reach groundwater in water wells increases.
Drought is a unique type of disaster because it is not a discreet event but rather is the cumulative result of a persistent period of below average precipitation. In the continental U.S. drought occurrence generally does not require evacuation nor does it constitute an immediate threat to life or property. The effects of drought may not be noticed immediately but only become apparent after weeks or months. The effect to the water table may take up to a year or more to be realized.
The most common impacts include economic hardship due to lost revenue from crops or loss of livestock. Non-irrigated croplands are most susceptible to moisture shortages. Grazing land and irrigated agricultural lands are not impacted quickly as the non-irrigated, cultivated acreage, but their yields can also be greatly reduced. Reductions in yields due to moisture shortages are often aggravated by wind-induced soil erosion.
In periods of severe drought, grazing land can destroy the economic potential of the livestock industry wildlife habitat in the fire areas. Under extreme drought conditions, lakes, reservoirs, and rivers can be subject to severe water shortages, greatly restricting their use for municipal water supplies.