CLIMATE CHANGE IMPACT ASSESSMENT ON WATERSHED HYDROLOGY: A COMPARISON OF THREE APPROACHES

Several methods of impact assessment have been developed over the years which basically incorporate future climate projections of atmospheric-ocean circulation based climate models into the simulation of land surface hydrological processes. This study attempted to evaluate three methods of climate change impact assessment: (a) Frequency perturbation method, (b) direct method and (c) delta change method. A well-calibrated hydrologic model, Soil and Water Assessment Tool (SWAT), was used in watershed simulation for climate projections of mid-century by ten Global Climate Models (GCMs). The frequency perturbation method found precipitation decrease by 17% and reduction in temperature by 0.43°C on an average annual basis. The changes when applied through the simulation model resulted in 13% reduction in Evapotranspiration (ET) and 25% reduction in water yield. Other two methods produced different set of results. It’s not conclusive to say which method performed better. The frequency perturbation method produced most extreme changes while direct method had the least magnitude of changes projected for the mid-century. Changes in ET and water yield due to changes in future climate are likely to have severe implications for the water availability. However, more research is needed to evaluate several other impact assessment methods for more reliable analysis.