Document Type : Research Paper
Authors
Abstract
On the basis of definition of United Nation Convention on Combating Desertification: desertification is land degradation on arid, semi-arid and sub- humid arid regions by reason of climate change and human activities. Also on the basis of this Convention, arid, semi-arid and sub-humid arid regions is regions that quotient between precipitation with potential evapotranspiration is approximately 0.05 to 0.65. Annual temperature averages and total annual precipitation from 45 synoptic meteorological stations for a 30 years period (1976-2005) has been collected the Meteorological Organization of Iran. In this paper for study of spatial spreading trend of arid and semi-arid climates of Iran of bioclimatic index of UNEP (United Nation Environment Programme) were used. Thirty years period divided to three subgroups: (1976-1985), (1986-1995) and (1996-2005). Then for each subgroup provided zoning maps and finally zoning maps were subtracted from each other. Results showed that: (1) The most spatial spread of arid and semi-arid climates observed in third decade and (2) The most severe changes of spatial climate observed in west and north-west and south-east of Iran, respectively.
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