A drought is a prolonged period of unusually low precipitation that causes water shortages.
Drought is not defined only by a fixed number of rainless days. Scientists compare precipitation, soil moisture, streamflow, reservoir levels, groundwater, and demand with local long-term conditions. A period that is severe in one climate may be normal in another, so drought definitions depend on place, season, and the impact being measured.
Meteorologists often distinguish meteorological, agricultural, hydrological, and socioeconomic drought. Meteorological drought concerns precipitation deficits; agricultural drought affects crops and soil; hydrological drought involves rivers, lakes, and groundwater; socioeconomic drought occurs when water scarcity disrupts people or economies. Heat can intensify drought by increasing evaporation and plant water loss.