Permafrost is frozen ground that remains at or below 0° Celsius for two or more years. In high-altitude regions, permafrost can underlie much of the landscape. Many people in the Hindu Kush Himalayas live near permafrost or in areas potentially affected by changes in permafrost.
Permafrost under high altitude pastures can retain water in the active layer, the uppermost ground layer that freezes in the winter and thaws in the summer, supporting vegetation such as mosses, lichens and dwarf shrubs. But when permafrost disappears, the water can drain freely, the ground becomes drier and vegetation changes, with impacts on herding communities and the ecosystem as a whole.
In the mountains, permafrost stabilizes rock slopes, moraines and debris-covered slopes. For instance, moraines consist of loose sediment often held together by permafrost. When permafrost thaws, slopes become more vulnerable to erosion. Debris and sediment may deposit slowly in nearby rivers or slide downhill catastrophically, destroying homes, bridges and roads. Loss of permafrost can also increase the likelihood of outburst floods of glacial lakes.
Permafrost thaw influences a broad range of systems, including hydrology, landscape evolution, vegetation, water chemistry, sediment loads in torrents and rivers, debris flows and rock fall. As a consequence, it can strongly affect regional livelihoods and economies. The impacts of permafrost thaw have been observed in many regions, including the European Alps, North and South America, Central Asia and the Arctic. But for the Hindu Kush Himalayas, published studies are few and relate mainly to the Tibetan Plateau in the context of highway and railway construction. To fill the knowledge gaps, ICIMOD is working to assess and better understand the dynamics of permafrost in the Hindu Kush Himalayas and its relationship to hydrology, hazards, ecosystems and livelihoods.