Modelling the potential impacts of climate change on hydrology and water resources in the Indrawati River Basin, Nepal

The Government of Nepal is planning to divert water from the Indrawati River Basin into the Kathmandu Valley to curb the decade-long water scarcity problem. However, climate change might alter water availability in the basin, hence affecting future water diversion strategies. Therefore, this study examines the potential impact of climate change on hydrology and water availability in the Indrawati River Basin of Nepal. The climate change scenarios from one regional climate model namely, HadGEM3-RA and two general circulation models namely, MIROC-ESM and MRI-CGCM3, each one under two different representative concentration pathways (RCPs), were fed into the Soil and Water Assessment Tool (SWAT) and hydrological changes were estimated for eight time frames: 2020s, 2030s, 2040s, 2050s, 2060s, 2070s, 2080s, and 2090s against the baseline period (1995–2004). The results show that the temperature in the basin could increase by 2.5–4.9 °C by the end of the century. The average annual precipitation in the basin is projected to increase in the future but the magnitude varies with time and the RCP scenarios. Similarly, the study shows an increase in annual discharge in both the Melamchi and Indrawati Rivers, but the monthly analysis reveals that the changes are not uniform. The discharge in the Melamchi River is projected to decrease during March–July and increase during August–February. In the Indrawati River the discharge is projected to decrease during November–April and increase during May–October. The findings show that the discharge into the Melamchi River during March and April will be sufficient for diverting water into the Kathmandu Valley. The results of this study will be useful for preparing an adaptation plan to offset the negative impacts, while at the same time harnessing the positive impacts of climate change in the basin.