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Analytical Overview
No analysis was completed for this map. Please note that there is no aridity zone data available north of 70 degrees.


Drylands: Aridity Zones of the World

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Using the ratio of mean annual precipitation to mean annual potential evapotranspiration, the world is divided into six aridity zones: hyper-arid, arid, semi-arid, dry sub-humid, and humid. As shown on this map, of the approximately 135 million km2 of terrestrial land area globally, the humid zone is the most extensive, covering about 46.5 million km2 (or 34 percent of total land area). This zone covers most of Europe and Central America, and large portions of Southeast Asia, eastern North America, central South America, and central Africa. The hyper-arid zone is the least extensive, covering approximately 11 million km2 (or 8 percent of total land area), and is represented most predominantly by the Saharan Desert. Hyper-arid lands generally are unsuitable for growing crops.

Drylands, as defined by the United Nations Convention to Combat Desertification (UNCCD), include the arid, semi-arid, and dry sub-humid zones and cover almost 54 million km2 of the globe. Semi-arid areas are most extensive, followed by arid areas and then dry sub-humid lands. These dryland aridity zones are spread across all continents, but are found most predominantly in Asia and Africa.
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Citation:
WRI. 2002. World Resources Institute. Drylands, People, and Ecosystem Goods and Services: A Web-based Geospatial Analysis. Available online at: http://www.wri.org
Sources:
  1. United Nations Environment Program/Global Resource Information Database. Prepared by U. Diechmann and L. Eklundh. 1991, Global Digital Datasets for Land Degradation Studies: a GIS Approach. Nairobi, Kenya:UNEP/GEMS and GRID.
  2. United Nations Environment Programme. 1997, World Atlas of Desertification, 2nd edition. London, UK:
  3. Office to Combat Desertification and Drought/ United Nations Development Programme. 1997, An Assessment of Population Levels in the World’s Drylands: Aridity Zones and Dryland Populations. New York, New York, USA: Office to Combat Desertification and Drought.