Summary : Drought is generally viewed as a sustained and regionaly extensive occurrence of below average, naturel water availability, either in the form of precipitation, river runoff or groundwater. Drought by definition consists of a sustained period of deficit wich may last a few months or even many years. However it is manifested, drought adversely affects the economy by reducing, or even eliminating, agricultural production, herds of cattle, and domestic and industrial water supply. Drought may be so severe that famine may ensue. Of the numerous aspects of drought, the present paper reports the single aspect of hydrological drought, i.e. the runoff of rivers deficit, with some attention to the precipitation deficit and the groundwater deficit. As stated above hydrological drought is considered to be a deficit of runoff below normal conditions, or else a depletion of aquifer levels even though, after over-exploitation, the water supplied by the aquifers may remain the same as before the drought. Five types of droughts may be distinguished based upon variations in the duration, sea-son of year, or severity. Last, some research projects are proposed in order to limit the consequences of hydrological drought. |
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