Development of a new downscaling method for hydrologic assessment of climate change impacts in data scarce regions and its application in the Western Ghats, India

Climate change affects local and regional water resources. Especially in regions with water scarcity, high climate sensitivity, and dynamic socioeconomic development, an adaptation of water management strategies is needed. Our study aims at (i) testing a new downscaling approach to utilize climate model results in a meso-scale hydrologic model and at (ii) analyzing the impact of climate change on the water balance components in the Mula and Mutha Rivers catchment upstream of the city of Pune, India. The new downscaling approach relies on the inherent consistency of both, the climate model and the measured data. It allows to derive a representation of a future climate scenario (2009-2099) by rearranging past measurements (1988-2008). We found a good agreement of the monthly statistics of the rearranged and the original measured data in the baseline period. However, the downscaling method is limited by the range of measured values provided in the baseline period, which results in an underestimation of temperatures in the last 20 years of the scenario period. The downscaled weather data for IPCC emission scenario A1B were used in a hydrologic impact assessment with SWAT. The scenario resulted in higher evapotranspiration, particularly in the first months of the dry season and in repeated low water storages in the reservoirs at the end of rainy season. Consequently, local and downstream water users as well as rain-fed agriculture and semi-natural vegetation in the Western Ghats increasingly suffer from water stress.