عنوان مقاله [English]
The Lake Urmia is the 20th largest lake and the second hyper saline lake in the world. In recent years, the drying out of the Urmia Lake has attracted attention of many researchers. The main motivation of this study is to evaluate the role of drought in this disaster. For this purpose, Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) are employed. The data for analysis including precipitation and temperature was provided from two global databases: GPCC for precipitation and NCEP/NCAR for temperature. The study was performed at the time span of 1980-2010 and the results showed that the Lake Urmia basin has experienced a severely drought during 1999-2000. After this period and during eight subsequent years, the negative effects of this drought could not be reduced completely by near normal to wet condition of the basin. Moreover, another severely drought occurred at 2008. RDI value for the 1999 drought was found to be -2.23 which is related to the extremely dry condition. The value of SPI for the same region and same year was obtained as -2.13. This comparison for other severe and extreme cases shows that RDI is more sensitive than SPI at the tails of the phenomenon. It was also observed that after 2000, while the region, in terms of rainfall and drought conditions, is generally close to normal condition, the lake follows a continuous decreasing trend up to the present time. Therefore, one can conclude that in addition to drought, other factors contribute to the drying out of the lake. The results indicated that the anthropogenic effects are responsible to some percent in this disaster. Construction of reservoir dams for agricultural development and other activities for job creation purposes like constructing fish ponds has intensified this crisis. The span of these activities is concurrent to the periods which the drought indices show the fragile condition of the basin in terms of available water resources. This fact emphasizes the importance of drought monitoring as an inseparable part of an IWRM program to prevent a nationwide disaster.