The flow of water that supports hydro-electric and irrigation projects in the mountain regions of India and Nepal is regulated by hundreds of large icy ponds on some of the world's highest glaciers, a study has found.
Researchers at Aberystwyth University in the UK have shown that the ponds, which form on debris-covered glaciers in the Himalaya, control the rate at which water from melting ice flows downstream.
With many covering an area of up to five times the size of an Olympic swimming pool, their hydrological role, specifically to the extent which they can store water on the glacier surface, has remained unknown until now.
According to Tristram Irvine-Fynn from Aberystwyth, the role of these ponds could become increasingly important as the region's climate changes.
"The hydrological role of ponds and debris may become more significant in the future. By understanding these processes we can become more confident in our predictions of water security and ecosystem response in the Himalaya," said Irvine-Fynn, who led the study published in the journal Geophysical Research Letters.
"Runoff from glaciers in the local region is an important freshwater supply and is used for agriculture and hydro- electric power," said Neil Glasser from Aberystwyth University.
"Water flowing from glacierised catchments in the Himalaya is a critical water resource for mountain dwellers in particular, and impacts on flows reaching the lowlands too," said Glasser.
Irvine-Fynn and colleagues uncovered the hydrological function of surface ponds on Khumbu Glacier in the Everest region of Nepal.
The team monitored the melt-water runoff from Khumbu Glacier, which descends from Mount Everest, for nearly 200 days through the summer monsoon season.
The high-resolution measurements of water flow showed two unexpected patterns: first, the water volumes released by the glacier were out of phase with daily solar radiation, and second, temperature cycles and the rate of change in runoff after peak flow did not decline smoothly.
"The pattern of melt-water flow decline, or the 'flow recession', was really intriguing and did not seem to match the patterns that have been reported for clean ice glaciers in the Alps or Svalbard in the Arctic Circle," said Irvine-Fynn....