The Investigation of Common Monitoring Meteorological Drought Indices in Four Consecutive Decades (1969-2011) A Case Study of Dez Watershed

Drought is a natural phenomenon and an integral part of climate change, being considered coupled with the scarcity of water resources in a geographical area in the period of time. In order to calculate of dry and wet years, annual precipitation data from 10 stations related to Dez watershed in Lorestan province was used during a period of 42 years 1969-2011). After selecting the concurrent period and evaluate the integrity of data, climate indices such as Standardized Precipitation Index (SPI), Standard Index Annual Precipitation (SIAP), Percentage of normal Precipitation Index (PNPI) and Nietzsche were used to determine drought and wet period. The results of this study indicated that the degree of drought is more severe and frequent in the second decade of the study (1981 -1991). Due to high sensitivity of SPI index to changes in rainfall and simply computing, and SIAP index because of high capabilities, less limitations and display lower levels of extreme drought in all stations in coincided with the years minimum Showed better efficiency in compared to other models. By using SPI index, 18 moderate drought cases, eight severe drought cases and one severe drought event was observed. Results for SIAP Indicators also showed the occurrence of 9 incident weak drought, moderate drought in 10 cases, 15 severe drought cases and 18 very severe drought cases.