The aim of this research is to study the spatial and temporal variability of aridity in Iran, through analysis of temperature and precipitation trends during the 48 years period of 1961–2008. In this study four different aridity criteria have been used to investigate the aridity situation. These aridity indexes included Lang’s index or rain factor, Budyko index or radiational index of dryness, UNEP aridity index and Thornthwaite moisture index. The results of the analysis indicated that the maximum and minimum of mean temperature occurred in July and January respectively in all locations. Among the study locations Ahvaz with 37.1°C and Kermanshah with 20.2 °C has the highest and lowest in July and for January, this value was 12.4 °C for Ahvaz and -4.5 °C for Hamedan and Kermanshah together, respectively. The range of monthly mean temperature of study locations indicated that, the maximum and minimum difference between day and night temperatures almost in all study locations occurred in September and January respectively and the highest and lowest fluctuation of temperature observed in Kerman and Tehran. The temperature anomalies showed that the most significant increasing temperature occurred at the beginning of twenty-first century (2000-2008) in all locations. The Long-term mean of monthly rainfall showed that in most study locations, the maximum and minimum of mean precipitation occurred in winter and summer respectively. Rasht with 1355 mm had the highest and Yazd with 55 mm had the lowest of total precipitation compared to other locations. According to precipitation anomalies, all locations experienced dry and wet periods, but generally dry periods occurred more often especially in the beginning of twenty-first century. Using different aridity indexes mentioned above, it is observed that all the study locations often experienced semi-arid to arid climate, severe water deficit to desert climate, arid to hyperarid climate, and semi-arid climate during the study period.

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