arid region

The Negev Desert in Israel. Although superficially barren, arid regions such as the Negev Desert support a remarkable diversity of plants and animals, all of which have developed highly specialized ways of coping with the harsh conditions.

The semi-arid landscape of southern Africa. In relatively dry areas such as this, weathering processes differ slightly from those in wetter places, such as northern Europe. The small amount of water available is enough for some freeze-thaw action, especially since the cloudless skies allow heat to escape at night. Occasional flash floods also help break down the rock.

The Atacama Desert in northern Chile. This cool, arid region, one of the driest parts of the world, stretches south along the Chilean coast. It lies between the low coastal mountains of the west coast and the foothills of the Andes in the east. A sandy area is shown here, but the region also contains pebbled pavements and salt pans.

In earth science, a region that is very dry and has little vegetation. Aridity depends on temperature, rainfall, and evaporation, and so is difficult to quantify, but an arid area is usually defined as one that receives less than 250 mm/10 in of rainfall each year. (By comparison, New York City receives 1,120 mm/44 in per year.) There are arid regions in North Africa, Pakistan, Australia, the USA, and elsewhere. Very arid regions are deserts.

The scarcity of fresh water is a problem for the inhabitants of arid zones, and constant research goes into discovering cheap methods of distilling sea water and artificially recharging natural groundwater reservoirs. Another problem is the eradication of salt in irrigation supplies from underground sources or where a surface deposit forms in poorly drained areas.