Supraglacial ponds regulate runoff from Himalayan debris-covered glaciers

Meltwater from glacierized catchments in the Himalaya is a vital freshwater resource for one fifth of the Earth’s population. Between 13% and 36% of the region’s glacierized areas are characterized by surface debris cover and associated supraglacial ponds whose hydrological roles remain unconstrained. We present a high-resolution meltwater hydrograph from the extensively debris-covered Khumbu Glacier, Nepal spanning a seven-month period in 2014. Supraglacial ponds and accompanying debris cover modulate proglacial discharge by acting as transient and evolving reservoirs. The supraglacial pond system may store up to 23% of observed mean daily discharge, with mean recession constants ranging from 31 to 108 hours. With projections of increases in debris-cover and supraglacial pond extent in the Himalaya, we conclude that runoff regimes may become progressively buffered by the presence of supraglacial reservoirs. Consideration of this process is critical to improve predictions of the region’s freshwater resource availability and cascading environmental effects downstream.