Estimating the Impacts and Uncertainty of Climate Change on the Hydrology and Water Resources of the Koshi River Basin

Abstract

In this study, projections of temperature and precipitation in future periods and their impacts on hydrology and water resources of the Koshi River Basin in Nepal were investigated. The statistical downscaling model Long Ashton Research Station Weather Generator (LARS-WG) was used to downscale low-resolution data from ten general circulation models (GCMs) and three IPCC SRES scenarios (B1, A1B, and A2). The physically based hydrological model Soil and Water Assessment Tool (SWAT) was used to analyse the impacts of climate change on hydrology. LARS-WG simulated the baseline period (1981–2000) climate quite satisfactorily. Changes in climate and hydrological variables are presented at monthly and annual scales for three future periods: 2011–2030, 2046–2065, and 2080–2099. The results indicate that the Koshi basin tends to become warmer in the future as projected by all GCMs under three SRES scenarios. Changes in precipitation and streamflow are not univocal and vary depending on the GCM, GHGES. The difference in the projection of flow varies by as much as −35 to 51 % under the A1B scenario during the 2055s. The maximum increase in flow is projected during spring season with increase of 23 and 25 % during the 2055s and 2090s, respectively, under the A1B scenario. Similarly, the range of projections for all water balance components is very large. The water balance components: surface flow, baseflow, and water yield may decrease or increase in future periods, as GCMs do not agree on the direction of change. The potential ET and actual ET are projected to increase as projections from all GCMs and scenarios indicate, although a great deal of uncertainty exists in the magnitude of change. The potential ET is projected to increase in the range of 6–24 % in the 2090s. There is high variability among the models and scenarios for projections, and the variability increases with future time periods.