An assessment of climate change impacts on streamflows in the Musi Catchment, India

Abstract

The long-term impacts of climate change on water resources are expected to be considerable in Southern India especially in the semi-arid regions. The effects of the changes on precipitation and temperature are expected to alter the hydrology of catchments and ultimately water security. A complicating factor in dealing with climate change from a water resource management perspective in India is the current government policies that promote watershed development (WSD), a policy that promotes the capture of runoff to increase groundwater recharge and irrigation development. In this paper the aim is to quantify the impacts climate change and WSD will have on the hydrologic behavior of the Musi catchment Andhra Pradesh. Global Climate Model (GCM) predictions of future climate are too coarse for hydrological modelling and fail to account for the most important influence on the monsoon rainfall patterns over India. In order to increase the spatial resolution of the models, a dynamic downscaling approach was used in this research. Three climate simulations corresponding to the IPCC-SRES A1B scenario were downscaled for the period 1961- 2098 using Providing REgional Climates for Impact Studies (PRECIS) regional climate modelling system. These simulations were based on three versions of the HadCM3 global climate model that showed realistic results for the Indian summer monsoon. The hydrology of the catchment was modelled using the SWAT hydrologic model. The model was set up for the entire Musi catchment in the Krishna Basin for which the model calibration and validation was carried out at the Osman Sagar and Himayat Sagar gauging stations. Monthly and annual inflows were used to carry out the model calibration. The model calibration and validation yielded Nash-Sutcliffe coefficients ranging between 0.65 and 0.75, which indicate a good model performance. The downscaled climate data was then used as forcing data in the model to carry out simulations for all three versions of the climate projection data ((Q0, Q1 and Q14). An analysis of flows at different time slices shows that stream flows decline in the near future (2011-40) and then an increasing trend towards the end of the century. Under the Q1 scenario, annual stream flows show a systematic decline over the period of analysis. The Q14 scenario shows an increase in stream flows over the next few decades followed by a decline towards the end of the century. Potential evapotranspiration is predicted to increase for all the climate scenarios. The reservoir component option available in SWAT was used to assess the impact of watershed development structures in the catchment and the analysis shows that stream flows have been declining due to the growth and impact of these structures in the catchment.