AskDefine | Define aridness

Dictionary Definition

aridness n : a permanent absence of rainfall [syn: aridity]

User Contributed Dictionary



  1. The state or quality of being arid.

Extensive Definition

In general terms, the climate of a local or region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life. As a result, environments subject to arid climates tend to lack vegetation and are called xeric or desertic. Juba, South Sudan is an Arid land.


The expression 'available water' refers to water in the soil in excess to the wilting point. The air over a hot desert may actually contain substantial amounts of water vapor but that water may not be generally accessible to plants, except for very specialized organisms (such as some species of lichen). 'Lack of water' refers to use by plants. The water that is actually present in the environment may be sufficient for some species or usages (such as climax vegetation), and grossly insufficient for others. Aridity, the characteristic nature of arid climates, may thus depend on the use of the land. Regards to the presence of life, what is more important than the degree of rainfall is the fraction of precipitation that is not quickly lost through evaporation or runoff. Attempts to quantitatively describe the degree of aridity of a place has often led to the development of aridity indexes. There is no universal agreement on the precise boundaries between classes such as 'hyper-arid', 'arid', 'semi-arid', etc.

Geographical distribution

If different classification schemes and maps differ in their details, there is a general agreement about the fact that large areas of the Earth are considered arid. These include the hot deserts located broadly in sub-tropical regions, where the accumulation of water is largely prevented by either low precipitations, or high evaporation, or both, as well as cold deserts near the poles, where water may be permanently locked in solid forms (snow and ice). Other arid regions include areas located in the rain shadows of major mountain ranges or along coastal regions affected by significant upwelling (such as the Atacama Desert).

Change over time

The distribution of aridity observed at any one point in time is largely the result of the general circulation of the atmosphere. The latter does change significantly over time through climate change. In addition, changes in land use can result in greater demands on soil water and induce a higher degree of aridity. See aridification.

See also


  • Griffiths, J. F. (1985) 'Climatology', Chapter 2 in Handbook of Applied Meteorology, Edited by David D. Houghton, John Wiley and Sons, ISBN 0-471-08404-2.
  • Durrenberger, R. W. (1987) 'Arid Climates', article in The Encyclopedia of Climatology, p. 92-101, Edited by J. E. Oliver and R. W. Fairbridge, Van Nostrand Reinhold Company, New York, ISBN 0-87933-009-0.
  • Stadler, S. J (1987) 'Aridity Indexes', article in The Encyclopedia of Climatology, p. 102-107, Edited by J. E. Oliver and R. W. Fairbridge, Van Nostrand Reinhld Company, New York, ISBN 0-87933-009-0.
aridness in Bosnian: Aridna klima
aridness in Czech: Aridní oblast
aridness in German: Arides Klima
aridness in Spanish: Clima árido
aridness in Basque: Basamortuko klima
aridness in French: Climat désertique
aridness in Galician: Clima árido
aridness in Korean: 사막 기후
aridness in Croatian: Aridna klima
aridness in Indonesian: Arid
aridness in Hebrew: אקלים צחיח
aridness in Georgian: არიდული ჰავა
aridness in Dutch: Droog klimaat
aridness in Japanese: 砂漠気候
aridness in Norwegian Nynorsk: Tørt klima
aridness in Portuguese: Clima árido
aridness in Russian: Аридный климат
aridness in Simple English: Arid
aridness in Serbo-Croatian: Aridna klima
aridness in Ukrainian: Аридний клімат
aridness in Turkish: Kurak
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