Analyzing climate change effects on drought occurrence in Yazd province, Iran

Water scarcity, climate change / global warming, and desertification are three big challenges which human is facing them. These problems have mutual impacts on each other as well. For example, in some regions, climate change causes frequent drought occurring which results in water shortage and consequently, if drought continues, results in desertification. Arid regions because of their sensitive ecosystem are more susceptible to climate change effects and Yazd province, located in central Iran, is one of the driest parts of the country. In this research, to understand how climate change affects droughts in the region, drought trend in Yazd synoptic station during 1966-2009 is surveyedusing nonparametric Mann-Kendall test. Drought, estimated by Reconnaissance Drought Index (RDI), is considered as a result of a decrease in input humidity (rainfall), an increase in output moisture (Potential Evapotranspiration (PET)), or occurring both of them (deficiency in rainfall and higher PET). The 3, 6, 9, 12, 18, and 24 month time series are applied and the results showed a rising trend of drought occurring which caused by precipitation decreasing and PET (calculated by FAO-Penman-Monteith) increasing. In spite of the general drought rising trend, the 1975-1995 period was remarkably humid rather than the rest of the period (i.e.1966-2009) which resulted by PET decrease. Analysis of the major parameters affecting PET revealed that in spite of temperature and sunshine hours increasing in period 1975-1995, wind speed and relative humidity showed a clear decrease and increase, respectively. This caused PET decreasing and consequently humidity increasing. In drought analysis under climate change, therefore, in addition to temperature and rainfall, some other parameters also may be effective and even overcome temperature and rainfall effects.