12. Distributed Hydrological Modelling Under Hypothetical Climate Change Scenario for a Sub-basin of the Brahmaputra River

A process-oriented hydrological model J2000 was employed on daily and monthly time steps for run-off simulation under Indian condition for the years 2003–2010. Further, a validated model was used for water balance assessment of the basin under both present scenario and hypothetical variations in precipitation and temperature. The regional sensitivity analysis (RSA) approach was employed for sensitivity analysis to determine the critical input parameter of the study area. It is inferred that recession coefficient for overland flow (soilConcRD1) is the most sensitive parameter, followed by recession coefficient for interflow (soilConcRD2) and linear reduction coefficient for AET (soilLinRed). Four evaluation criteria, i.e. coefficient of correlation (R), Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS) and root-mean-square error (RMSE) observation standard deviation ratio (RSR), were adopted, for judging the model’s performance. For daily time steps, the PBIAS, R, NSE and RSR were found to be 4.73, 0.85, 0.67 and 0.45, respectively, during calibration and −1.50, 0.92, 0.85 and 0.29, respectively, during validation of the model. For monthly time steps, the PBIAS, R, NSE and RSR were found to be 4.73, 0.88, 0.7 and 0.43, respectively, during calibration and −1.50, 0.94, 0.89 and 0.26, respectively, during validation of the model. Further, model-simulated run-off components are overland flow (RD1), model’s interflow components (RD2 and RG1) and baseflow component (RG2), and the percent contribution was found to be 43.1 %, 35.8 % and 21.1 %, respectively. The water balance analysis carried out in the study demonstrated that the annual average precipitation in the basin is about 1,388 mm, out of which about 21 % flows out as run-off, 22 % as groundwater and about 56 % as evapotranspiration. The higher value of evaluation criteria indicates that the model is efficient in imitating the hydrological phenomenon of the Kopili River basin fairly well and can be cogitated as a promising tool to understand the constantly changing hydrological processes of Northeast (NE) India. Moreover, the hypothetical temperature increases due to the lowest emission scenario (1.1–2.9 °C), and the highest emission scenario (2.4–6.4 °C) of the IPCC (Climate change 2007: the physical science basis. Contribution of working group I. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge, UK, 2007) indicates that the higher evapotranspiration is mainly resulting in low surface run-off and groundwater contribution. The run-off fluctuations resulting from ±10 % variation in precipitation were also analysed and were found to be approx. ±18 % deviation from simulated run-off. This analysis will be useful to understand the verge of hydrological processes in anticipation of global climate change (CC) and finally for sustainable water resource management in the NE region of India.