Submitted to: Oxford Companion to the Earth
Publication Type: Book / Chapter
Publication Acceptance Date: 12/1/1999
Publication Date: N/A
Interpretive Summary: Arid zones are the areas of the world too dry for cultivated agriculture. These zones are generally found along two wide belts at approximately 30 degrees north and south of the equator. These latitudes include the major deserts of the world. Arid zone hydrology is the study of the water balance; the relation between average annual precipitation and soil moisture, flow in streams and rivers, plant water use, and recharge of ground waters. Arid zone hydrology is shown to be unique and quite different from the study of water in more humid areas.
Technical Abstract: Arid zones are defined in terms of the mean annual distribution of precipitation and temperature. The global distribution of arid zones is described in relation to their distribution in the northern and southern hemispheres in the zones of subsidence. The role of geology in determining arid zone landscapes is described and a watershed is defined. Arid zone watersheds are defined using the mean annual water balance under conditions where the potential evapotranspiration exceeds the annual precipitation.