Comparison of Rainfall and Evapotranspiration-Based Drought Indices to Determine Meteorological Drought

Monitoring systems are one of the tools required in drought management practices. With these systems, through the application of drought indices, it is possible to determine the intensity and the development of a drought location. In this study, RAI, DPI, PN, SPEI, SIAP, and SPI drought indices were used for quantitatively quantifying drought and its zoning in 10 selected weather stations in Iran. First, rainfall data of 1980 to 2013 was collected from local authorities. Then, each of the indicators were calculated and the severity of drought for the statistical period was evaluated. Spearman correlation coefficient, between the drought index and rainfall changes, was used to select the most suitable index. Spearman correlation coefficient showed that in the synoptic stations of Tehran, Zahedan, Kerman, and Yazd the SIAP index; in Gorgan, Rasht, and BandarAbbas stations the SPEI index, and in Sanandaj, Birjand, and Urmia the RAI index were superior in detecting the severe and very severe droughts when compared with the other indices. In correlation analysis of the coupled indices, in most of the stations, the couples of RAI-SPEI, RAI-SIAP and SPEI-SIAP indices were highly correlated and the correlation of other indicators was weak. Overall, the DPI and PN indices showed high suitability in capturing the normal years, while the RAI, SPEI and SIAP indices were better at estimating the droughts.