-Drought Trend Assessment in Riverheads of Karkheh and Dez Basins Based on Streamflow Drought Index (Sdi)

This paper focused on the phenomenon of drought defined by the streamflow drought index (sdi) at hydrometric stations in riverheads of karkheh and dez basins in lorestan province. for this purpose, the monthly discharge data from 21 hydrometric stations were used over the period 19752011. the mannkendall and sen’s estimate methods were applied to explore the trends in the time series of 12 months. the results showed that detection of the drought trend has been almost the same in both methods. so that 70% and 100% of stations in karkheh dam had significant trend based on mannkendall method and sen’s estimate approach, respectively. but this amounts in dez dam for mannkendall and sen’s estimate methods were 58% and 78% respectively. the stations of dare takht (marbareh), dorud (tire) and dorud (marbareh) in dez dam basin suffered from the highest intensity trend of hydrological drought. the stations of doab (vesseyan), horo (kaka reza) and tang syab in karkhe dam basin also had the highest intensity of hydrological drought. based on these results, karkheh dam has spent more severity and a long time of water deficit in recent years. according to the position and distribution of the stations in the study area this two studied dams have a special spatial trend.