Basinwide Comparison of RDI and SPI Within an IWRM Framework

This study intends to evaluate the performance of RDI and SPI in Lake Urmia Basin, Iran. The data base used in this research was GPCC for precipitation and NCEP/NCAR for temperature. This study aims not only to evaluate the performance of RDI and SPI, but also to find out the reason of Urmia Lake drying up as second largest hyper saline lake in the world. According to the results, Urmia Lake basin faced the most severe drought condition in the past half century in 1998-2000, and afterwards it could not enter into a suitable wet state during the later years. Although it was found that both SPI and RDI performance in drought recognition was acceptable and matched in many cases; nevertheless, it was concluded that RDI is more sensitive to severe drought. While SPI had no long term trend, RDI showed negative trend and an abrupt change in around 1996 which could be addressed as a consequence of global warming. These characteristics gave a better perspective of drought phenomenon across the basin and introduced RDI as a conservative and reliable tool for studying drought in the Urmia Lake basin. In this study, it was acknowledged that drought cannot be the only reason for the lake drying up, because it was indicated that precipitation over the basin has been close to its long-term average in recent years while the lake level is continuously declining. Human activities such as dam construction during the drought periods, and also activities like extensive fish farming in rivers leading to Urmia Lake and overexploiting of surface and groundwater resources could be effective in intensifying the natural drought effects. The Current status of the Urmia Lake, once again emphasizes the importance of integrated water resources management and establishing a drought monitoring system in all basins, in which using indices like RDI can play a fundamental role.