Spatial pattern of droughts intensity and direction variations using trend analysis of Distributed Self-Calibrated Palmer Drought Severity Index in Iran

Drought has been always known as one of the most important threats for civilizations in Iran. Several indices based on meteorological data, satellite data and simulation model has been introduced for detection of drought extension. In this study, spatial distributions of PDSI (Palmer Drought Severity Index) patterns were derived for a 36-year-period (1975-2010) using gridded soil properties and meteorological data consists of 296 synoptic stations and more than 1500 rain gage stations with 4 km spatial resolution. The calculations were performed using an automated interface program developed in MATLAB. To see the drought pattern intensity and its direction spatially, a regression trend analysis was performed in monthly and general time steps pixel by pixel. The results indicated that during the 36-year-period more than 60 percent of the area had a downward trend (increasing droughts) and less than its 4 percent shows upward trend. The slope of trends was variable between -0.22 and 0.12.