Study of Aridity Index Trends in Southern Half of Iran

The objective of this research was to study simultaneous trends of precipitation and evapotranspiration in the frame of aridity index at southern half of Iran. The time period of this study was from 1961 to 2000. Preliminary results of the synoptic stations time series revealed that the variation of evapotranspiration was less than other two factors (precipitation and evapotranspiration). At the next stage non-parametric Mann-Kendall trend test was conducted for detecting the trends of each factor. Results showed that there was an upward trend for precipitation; however، there was a downward trend for evapotranspiration in almost all stations. Furthermore، trends were statistically significant for about 70% of sites in the cases of precipitation and aridity index and for about 90% of sites in the case of ET0. Trend analysis of aridity index showed that the climate of nearly all sites (about 80%) had tendency to a humid climate to some degree. Mann-Kendall trend diagrams revealed that for all sites the year 1963 was the starting point of trend. Both the maximum and minimum values of significant trends of the three parameters belonged to Esfahan and Ahwaz، with steppe and desert climates.