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

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.