Hydrological Response to Environment Change in Himalayan Watersheds: Assessment from Integrated Modeling Approach

Land use changes such as deforestation, increase in cropping or grazing areas and built-up land, likely modify the water balance and land surface behavior in the Himalayan watersheds. An integrated approach of hydrological and hydraulic modeling was adopted for comparative analysis of hydrological pattern in three Himalayan watersheds i.e. Khanpur, Rawal and Simly situated in the Northern territory of Pakistan. The rainfall-runoff model SWAT- Soil and water assessment tool and HydroCAD were calibrated for the selected watersheds. The correlation analysis of the precipitation data of two climate stations i.e. Murree and Islamabad, with the discharge data of three rivers was utilized to select best suitable input precipitation data for HydroCAD rainfall-runoff modeling. The peak flood hydrograph were generated using HydroCAD runoff to optimize the basin parameters like CN, runoff volume, peak flows of the three watersheds. The hydrological response of the Rawal watershed was studied as a case study to different scenarios of land use change using SWAT model. The scenario of high deforestation indicated a decline of about 6.3% in the groundwater recharge to stream while increase of 7.1% in the surface runoff has been observed under the scenario of growth in urbanization in the recent decades. The integrated modeling approach proved helpful in investigating the hydrological behavior under changing environment at watershed level in the Himalayan region.