The Investigation of Drought Values Fluctuation under the Effect of Climate Change—Case Study: Gharesou Basin

This research evaluates climate change effects on drought severity in the region of Gharesou,Iran. The Standardized Precipitation Index (SPI) has been used for estimation of drought severity. A geographical information system is applied for calculating the mean areal precipitation timeseries from 11 meteorological stations, in or out of the area for the hydrological period Jan 1971-Dec 2000 using Inverse Distance Weighting method. This precipitation timeseries have been used for the estimation of Standardized Precipitation Index (SPI) for three timescales, 6-, 12and 24-months, for the region. The outputs of HadCM3, one of the AOGCM models, were applied for a socioeconomic scenario, namely, SRES A2 for the assessment of climate change impact on droughts. The HadCM3 outputs were downscaled statistically to the region of Gharesou using SDSM software to estimate precipitation timeseries for a future period 20402069. A method has been used for the estimation of annual cumulative drought severity-time scale-frequency curves. These curves integrate the drought severity and frequency for various types of drought. The SPI timeseries were estimated and compared with the respective timeseries of the historical period 1971-2000. The comparison indicated that the drought intensity and severity decreases for all examined SPI timeseries. Furthermore, analysis of drought period has shown that the value and frequent of the drought would be declined in future in the region.