Severity Duration Frequency Curves Analysis of Drought Case Study: South -West Chosen Stations of Iran

Drought is a recurrent feature in different climates, occurrence of drought do not limited to specific regions on times it should be possible in the region with high – rain in each seasons of the year. One of the most important stages of drought monitoring is to identify the indices to analysis severity – duration and frequency of drought events. This paper evaluates the Standardized Precipitation Index (SPI) on 3, 6, 12, 24 and 48- month scales using monthly precipitation totals for 10 stations in south-west basins of Iran from January 1960 to December 2000. Severity-Duration curves, as well as return periods were extracted for each station. Severity maps showed that in the east and the south of the region, drought intensity is more than other areas. The results show that when SPI index have negative sequences, drought will occur and when SPI values are -1 or less, drought occurrence is severe. These time scales explain the impact of drought to availability of water resources. Thus the reaction of soil moisture to precipitation occurs in short time while the response of underground water and stream flows are a long term processes.