Assessment of Historical and Future Water Availability in Himalayan Tamor River Basin Nepal Utilizing CMIP5 CNRM Climate Model Experiments

Abstract

In this study, the assessment of water availability under climate changing environment has been done in the Himalayan Tamor River Basin, Nepal using physically based, spatially distributed, a continuous model 'Soil and Water Assessment Tool' (SWAT). The hydrological simulation and projection have been performed in the historical (1996-2007) and future times (e.g. 30s, 40s, 50s, 60s, 70s, 80s, 90s). The climate change impact assessment on the hydrology of Tamor river basin has been performed utilizing the CMIP5 CNRM climate model datasets (with RCP4.5 and RCP8.5). The model calibration and parameterization uncertainty evaluation in the simulated and projected flows were done in SWATCUP using SUFI2 algorithm. The results obtained from the model calibration (1996-2004) and validation (2005-2007) showed a reliable estimate of daily streamflow for calibration period (R2 = 0.85, NSE =0.85 and PBIAS=-2.5) and validation period (R2 =0.87, NSE =0.85 and PBIAS=-5.4). The average annual water yield at the main outlet of the basin is computed as 1511.13 mm, and the total annual quantity is recorded as 6.25 BCM. The average annual precipitation over the seleced river basin is projected to be increased in all scenarios. The stations at higher altitude show more temperature rise than those at a lower elevation and thus there would be minimal snowfall has been projected in the basin by 2100 AD under both scenarios (RCP4.5 and RCP8.5). It is expected that the flow pattern in the future would be similar to the baseline pattern under all scenarios. The baseflow will be dramatically increased in all scenarios, but the lowest flow month would be shifted from March to February. Since the base flow during lean months would be increased in future as projected by all scenarios, there would not be adverse impacts on higher percentile flows. This study would be useful for the assessment of the possibility of storage type or run-off-river type hydro-project in the basin in terms of water availability.