Modeling the impacts of natural and anthropogenic processes on the hydrologic components in Kordan watershed, Iran

The objective of this study was to investigate impacts of climate disturbance and watershed management operations on hydrologic functioning of the Kordan watershed in Iran. Soil and water assessment tool was used and evaluated for an 18-year monthly stream discharge. Statistical and graphical analysis of the calibrated and validated model presented appropriate fit to the measured data (NSE and R² were more than 0.80), allowing reproduction of the historic hydrological conditions of the watershed for future analysis. A 12-month timeframe was achieved from correlation between standardized precipitation index and standardized runoff index to quantify drought characteristics and define drought disturbance scenarios. Replacing normal periods in terms of precipitation amount with extreme and severe periods up to 40% resulted in declining monthly flow out by 24% and 21%, respectively. Pasture restoring scenarios resulted in a significant decline in amount of surface runoff. Replacing 50% of poor rangeland areas with moderate rangeland caused monthly amount runoff to decline by 16%. The percentage of runoff decline raised up to 44% by replacing moderate rangeland thoroughly. Furthermore, land-use scenarios increased amount of subsurface flow considerably. Impacts of constructing hydraulic structures were assessed in each sub-basin separately. Results showed decline in yearly surface runoff varied from 50 to 97%, depending on the volume of structures and sub-basin characteristics. The findings would be beneficial to decision makers which contribute to better understanding of natural and man-made activities on hydro-power potential of watersheds.