Comparative Study of Efficiency of Some Meteorological Drought Indices in Different Climate Regions of Iran

The present study aimed to investigate the periodic behavior, frequency and severity of drought along with introducing one or several adopted indices for each climate region in Iran. Daily data of 42 synoptic weather stations for a 23-year statistical period (1993-2016) were used in this study. Using the "efficient measure" hypothesis, the drought characteristics of each climate zones were investigated in the country. The years 1999-2000 in the arid zone and 2007-08 in other climate types were considered as a year of widespread drought throughout the country. According to "efficient measure", the results showed that the percentage of normal precipitation index (PNPI) was not a suitable indicator, especially for humid regions. Whereas, the standardized Precipitation Evapotranspiration index (SPEI) showed better performance on drought monitoring in wetter regions. Unlike the performance of other indices, the standardized precipitation index (SPI) had the same results in drought monitoring in all climates. This finding does not seem logical and indicates that the use of SPI should be done more carefully. With regard to the droughts persistence, except for the Chinese-Z index which in some cases showed completely opposite results in the wetter and dry periods, not all indices differed significantly. In addition, the results of this study revealed that the pattern of drought changes was not periodic.