Diagnosis of the Past, Present and Future Hydrology of a Glaciated High Mountain Headwater Basin in Central Asia

Abstract

This study used the Canadian physically based hydrological land surface scheme MESH for a comprehensive representation of high mountain hydrological processes such as glacier energy balance and ablation, blowing snow, energy balance snowmelt and frozen ground in Kyrgyzstan's partly glacierised basin Ala-Archa. Historical and future changes in the basin's hydrology were diagnosed through inter-comparisons of the hydrological processes in three periods of past (1961–1980), current (1991–2010) and future (2081–2100), with respect to the dynamics in climate and glacier coverage. Glacier maps from 1970 and 2000 were used for glacier configurations of the model in the past and present periods, respectively. Impacts of future glacier changes were evaluated through a static assumption to a fully retreated assumption. For historical and present simulations, the MESH model was forced by the EM-Earth (0.1°) and ERA-5 (0.25°) reanalysis data, whilst for the future simulation, monthly perturbations in temperature and precipitation were applied to the observations in 1991–2010 using the average delta changes derived from outcomes of an RCP 8.5 scenario in the CMIP5-AR5 subset (40 GCMs). Results show that the annual peak SWE has declined by 25% from the 1960s to the 2010s, whilst that in the future would show a much smaller decrease (5%). However, the timing of peak SWE in the 2100s is predicted to advance about 1 month and the snow cover duration to decline by 2 months in comparison to the 2010s. The timing of peak streamflow is expected to advance from July to June, and the annual and summer streamflow volume would decrease by 52% and 67%, respectively, under the fully retreated glacier assumption. These results underline the need for renewed diagnostic assessments of water supply in high mountain headwaters of Central Asia to inform adaptation to climate change.