Glacier-influenced hydrological regimes in the Afghanistan Hindu Kush Himalaya under current and future climate

Abstract

Glaciers in the Hindu Kush Himalaya (HKH) are important freshwater resources. Glacier recession may lead to a significant decrease in summer runoff. This study focuses on Afghanistan in the western Himalayas with an arid to semi-arid climate, where, despite strong societal and ecosystem dependance upon mountain water resources, the contribution of glacier melt is poorly known. This study used a new conceptual precipitation and ice melt-runoff model to assess current and future streamflow, taking into account the effects of debris-covered ice. Three catchments with varying glacier cover are considered: Sust (4,609 km2, 15.6% glacier cover) in eastern Afghanistan; the Taqchakhana (264.4 km2 area, 2.8% glacier cover) in northern Afghanistan; and the Bamyan (325.3 km2, 0.7% glacier cover) in central Afghanistan. Results identified different annual hydrological regimes, with glacier runoff dominating Sust (76%), rain and snow runoff dominating Taqchakhana (50%), and baseflow dominating Bamyan (61%). Under RCP 2.6, glacier runoff in Sust and Taqchakhana is expected to increase until 2050, then decline as temperatures stabilize; under RCP 8.5, a more significant increase is projected, while runoff in Bamyan will decrease throughout the century. Catchments may experience a peak water phase due to both temperature effects and progressively diminishing size of glaciers.