Drought -- National Drought Mitigation Center




Date of this Version



Published in Encyclopedia of Earth System Science, vol. 2, edited by William A. Nierenberg, pp. 81–92 (San Diego: Academic Press, 1992).


Copyright © 1992 by Academic Press, Inc.


Scores of definitions of drought exist, reflecting different applications and regions of con-cern. Common to all types of drought is the fact that they originate from a deficiency of precipitation that results in water shortage for some activity (e.g., plant growth, transpor-tation) or some group (e.g., farmer, water suppliers). Drought can be defined as a defi-ciency of precipitation from expected or “normal” that, when extended over a season or longer period of time, is insufficient to meet the demands of human activities. Drought must be considered a relative, rather than absolute, condition. The ultimate results of these precipitation deficiencies are, at times, enormous economic and environmental impacts as well as personal hardship. Scientists speculate that the frequency and severity of droughts may increase if projected changes in climate occur because of increasing concentrations of CO2 and other atmospheric trace gases.