Investigating the impact of climate change on hydro-climatological variability and water resources in the Upper Indus Basin

Abstract

The Indus is crucial for Pakistan; economically and for water and food security. This thesis makes substantial contributions to fundamental understanding of local hydro-climatological processes in the Upper Indus Basin (UIB), essential as changes to water resources potentially affect millions of people. Drawing on a range of available data sources, complex vertical gradients are identified in several climate variables including cloud cover. The study confirms previously identified seasonally and diurnally asymmetrical temperature trends, which result in year round increasing diurnal temperature range, continue to the recent record, and describes some of the underlying causal mechanisms. Furthermore, for the first time, a stochastic weather generator is used to provide downscaled time series for 2071-2100 for two contrasting “climate scenarios” for the UIB: (i) using change factors from a Regional Climate Model (RCM) under the SRES A2 emissions scenario, (ii) extrapolating from recent observed climatic trends. A new semi-distributed basin-scale hydrological model is assembled using existing and adapted model algorithms to simulate cryosphere-hydrology interactions, including snowmelt and basic glacial mechanics. Calibrated catchment models – one glacial (Hunza) and one snowmelt-dominated (Astore) regime – are run to provide probabilistic estimates of potential hydrological changes. The RCM-derived scenario – featuring strong summer warming (> 5°C) – projects large decreases in glacial volumes (>90% and >80% mass loss in Astore and Hunza respectively) and one month earlier peak flows. The historical trends-based scenario – featuring net annual warming (0.7°C) but moderate summer cooling (~1.5°C) – also projects earlier peak flows but stable glacial areas and suppression of summer runoff from energy input constraints on melting.