Assessment of Standardized Precipitation Evapotranspiration Index (SPEI) for Drought Identification in Different Climates of Iran

There is a need of monitoring and analysis of drought condition for water resources management. Given the large difficulties to objectively quantify drought characteristics such as duration, intensity, and magnitude several drought indices have been developed in the last decades. One of shortcomings of current drought indices including standardized precipitation index (SPI) is that it does not include water balance by means of evapotranspiration. Standardized precipitation evapotranspiration index (SPEI) includes water balance in calculating of drought index using precipitation and evapotranspiration.The objectives of current study are to investigate meteorological droughts using SPEI in ten synoptic stations in different climates of Iran and to compare the results with SPI. In view of this, temperature and precipitation data in a long term 1975 to 2007 were prepared and the drought indices were calculated. The comparison was done based on indices values and drought categories class. The results showed that both SPI and SPEI indices have significant correlation, moreover the SPEI showed the quick response to drought. The increasing the timescales of indices also increase the duration of drought. Based on the importance of evapotranspiration in arid and semi-arid regions, the SPEI can be used as a suitable index for determining of droughts. However, further researches are needed in spatial and temporal scales.