Bias Correction Methods for Hydrologic Impact Studies over India’s Western Ghat Basins

The regional climate models (RCMs) used in the analysis of the impact of climate variables on the hydrology of river basins needs appropriate preprocessing (bias correction) to represent and reproduce future climate with a fair degree of accuracy. The performance of bias corrections methods was assessed in this investigation on the basis of their ability to minimize error on climate variables and streamflow. This work compares the performance of five bias correction methods applied for precipitation and four methods for temperature in modeling the hydrology of the river catchments of the Western Ghats of India. The Western Ghats are a mountainous forest range along the entire west coast of India that plays a major role in the distribution of Indian monsoon rains. Simulations were used to evaluate the performance of the bias correction methods. Using raw RCM, bias corrected precipitation and temperature time series, streamflows were estimated by the soil and water assessment tool (SWAT) hydrological model. The results indicated that the raw RCM-simulated precipitation was biased by 42% and the temperature was biased by 12% across the catchments investigated. Subsequently, a bias of 65% was found in the streamflow. The performance of the delta change correction method was consistently better for precipitation (with Nash-Sutcliffe efficiency, $\mathrm{NSE}>0.75$ for 5 catchments) and temperature ($\mathrm{NSE}=1$) compared with other methods. Good performance was observed between the observed and bias corrected streamflow (daily time scale) for the catchments Purna ($\mathrm{NSE}=0.97$), Ulhas ($\mathrm{NSE}=0.64$), Aghanashini ($\mathrm{NSE}=0.82$), Netravathi ($\mathrm{NSE}=0.89$), and Chaliyar ($\mathrm{NSE}=0.90$); low performance with an NSE of 0.3 was observed for the catchments Kajvi and Vamanapuram. The methods failed for Malaprabha and Tunga catchments. The results indicate that the delta change correction method performed best in analyzing the hydrological impact of climate variables on the windward side of Western Ghats of India.