Evaluation and Comparison of Drought Indices and Determination the Suitable Index in Zayandehroud Basin

Determination of indices is one of the basic and important steps in the study of wet and drought in each area. Indices can be evaluating the severity and duration of drought, and then the effect of them is determined on the water resources of the area. In this study, meteorological indices (Root Mean Square Error, Percent of Normal Precipitation Index, Rainfall Anomaly Index, Standardized Precipitation Index, DI, PNPI, and SIAP) was calculated using data of eight synoptic stations. The names of the stations are Meime, Varzane, Esfahan, Daran, Koohrang, Shahrekord and Shahreza in Zayandehroud watershed. Then for determine of the most suitable index in Zayandehroud watershed, meteorological drought indices using the minimum of precipitation and correlation methods were evaluated. The results of meteorological drought indices showed that the percentage of drought is different using different indices, as the RAI, DI, BMDI, SPI, SIAP showed that 35 to 45, 30, 20 to 40, 15 to 25, 25 to 35 percent of studied years are drought, respectively. RAI, BMDI, SPI and SIAP showed the highest percentage of occurrence of drought in Shahreza, Varzane, Abadeh and Varzane, respectively. DI index had equal percent of drought in all station except for Daran and Kuhrang stations. Finally, by the attitude of the two methods at the same time, was determined that meteorological drought of RAI and SIAP are better Indices than other drought indices.