Drought

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Drought is a temporary hazard of nature occurring from a lack of precipitation over an extended period of time. Drought differs from aridity, a permanent feature of climate restricted to regions of low rainfall. Rainfall deficiencies caused by a drought create a severe hydrologic imbalance resulting in considerable water shortages.

The beginning of a drought is typically determined by comparing the current meteorological situation to an average based on a 30-year period of record. This "operational" definition of drought allows meteorologists to analyze the frequency, severity, and duration of the aberration for any given historical period and aides in the development of response and mitigation strategies.

The agricultural sector is usually the first to be affected by dryness, since crops are heavily dependent on stored soil water. Jim Sugar. Jim Sugar Photgraphy/Corbis-Bettmann. Reproduced by permission.

Characteristics of drought are highly variable from region to region, depending on atmospheric factors such as temperature, wind, relative humidity, and amount of sunshine and cloud cover. High temperatures and lots of sunshine can increase evaporation and transpiration to such an extreme that frequent rainfall is incapable of restoring the loss. Meteorological definitions of drought, therefore, may deviate from operational definitions and are usually based on the length of the dry period and the degree of dryness in comparison to the daily average.

Drought is more than a physical phenomena; an extended period of dryness can have a significant socioeconomic impact. Drought presents the most serious physical hazard to crops in nearly all regions of the world. The agricultural sector is usually the first to be affected by dryness, since crops are heavily dependent on stored soil water. In addition to a decline in agricultural products, a shortfall in the water supply can disrupt availability of other economic goods such as hydroelectric power. The 1988–89 Uruguay drought resulted in a significant decline of hydroelectric power because the dryness disrupted the streamflows needed for production.

Hydrologic Cycle