Spatial trends in surface runoff and influence of climatic and physiographic factors: A case study of watershed areas of Rawalpindi district

Effect of climatic and physiographic factors on surface runoff is critical to study for soil conservation and water harvesting. In this study, the spatial variations of climatic and physiographic factors and their spatial correlation with surface runoff was investigated. The rainfall and temperature records were used for mapping climatic factors. Digital Elevation Model (DEM) was utilized in estimation and mapping of physiographic factors as well as watershed delineation and runoff estimation. The models were generated using runoff and influencing factors (rainfall, temperature, slope and elevation). The relationship between runoff and influencing factors was derived by developing statistically sound regression models. The spatial correlation indicated that the maximum surface runoff was generated in the areas receiving high rainfall (>1450 mm) whereas, runoff tend to decrease with rise in temperature above a certain value (18 ˚C ). The runoff also showed significant variability with slope and elevation changes. Maximum change in runoff was predicted by one unit change in temperature followed by elevation, slope and then rainfall. The regression model was found to be adequately fit to the predicted runoff by using influencing factors. The study identified potential water harvesting sites for sustainable water supply in Rawalpindi district.