Future scenario analysis of streamflow in a humid tropical river basin using a distributed hydrological model

Abstract

Water resource in the world is likely to be affected by the increasing concentration of greenhouse gases in the atmosphere. The General Circulation Models (GCMs) having large scale resolutions are the best available tools to provide estimates of the effects of rising greenhouse gases on rainfall and temperature. Yet, the spatial goal of these models (250km x 250km) is not good with that of hydrologic models. The yield from GCMs is downscaled utilizing Regional Climate Models (RCMs), which are provincial based, in this manner anticipating the yield to better goals (25km x 25km). A general methodology is proposed for using the downscaled outputs from a RCM in hydrologic models for assessing the impact of climate change on water resources. In the present work, the outputs obtained for two scenarios, A2 and B2 are used by the RCM to predict future climate changes. Two important climate variables, viz. rainfall and temperature are thus generated. These are then used to estimate the influence of climate change on streamflow by coupling with a hydrologic model called SWAT. The area selected for this research is a part of the Chaliyar river basin in Kerala. The model is calibrated with observed data for the period 1995–2001. Results show Nash–Sutcliffe efficiency (ENS) of 0.99 for stream flow. The coefficient of determination (R2) is also 0.99 for stream flow. The model is then validated for the period from 2002 to 2004 and its performance is found to be reasonably good. The average annual stream flows are predicted to decrease by 84.67% and 94.03% in the A2 and B2 scenarios respectively.