In the Hindu Kush Himalayan (HKH) region, many people live near permafrost or in areas potentially affected by changes in permafrost (Figure 1). Permafrost is ground material (rock or soil) at or below 0°C for two or more years. The near-surface layer above it thaws during the warm season and is termed the “active layer”. Permafrost thaw as a consequence of climate change will have societal, economical, and biological impacts in this area.
Permafrost is ground material (rock or soil), frequently mixed with ground ice, at or below 0°C for two or more years. The near-surface layer above it thaws during the warm season and is termed the “active layer”. The existence and characteristics of permafrost depend on the climatic setting, topography, surface cover and subsurface material. Permafrost is not visible at the surface making it challenging to map its occurrence and extent. Hence,a change in it can lead to unexpected impacts.
Permafrost thaw influences a broad range of systems including hydrology, landscape evolution, vegetation, sediments load in rivers, debris flows and rock fall, and water chemistry. As a consequence, it can strongly affect regional livelihoods and economies. Due to the tight coupling of atmosphere and subsurface temperature, widespread permafrost thaw during the coming decades can be regarded as virtually certain in the HKH region.
Permafrost stabilizes rock slopes, moraines and debris covered slopes, by adding cohesion and by preventing the build-up of hydrostatic pressure. Therefore, melting permafrost can have manifold consequences. For example permafrost under high altitude pastures can retain water in the near surface and make it available to vegetation during summer when the top layer of the permafrost thaws. When permafrost disappears, the water can drain freely, and the ground becomes drier and subsequently vegetation changes.
Especially glacial lakes or hydropower dams in the vicinity of mountains with permafrost will see an increase in rockfall hazards, which may lead to outburst floods with grave downstream consequences. In addition, moraines consist of loose sediments of various sizes, which are often held together by permafrost. When permafrost in moraines and debris slopes thaws, the sediments become available for transport, erode easily and are deposited in lower reaches of rivers. This can happen as a slow and steady process, or as a catastrophic event in combination with extreme precipitation, which can form debris flows with high forces possibly destructing downstream infrastructure such as houses, bridges and roads.
Figure 1: Permafrost and glacier in the extended HKH region (based on Gruber, 2012).
Visit http://www.geo.uzh.ch/microsite/cryodata/pf_global/ to obtain the 1km permafrost map for Google Earth or as a web mapping service.
Study methods include literature review in collaboration with partners, systematic analysis of freely available remote sensing imagery to assess the modelled permafrost distribution, and collection and documentation of permafrost and air temperature data and its metadata. Based on this and a workshop, recommendations will be developed for future projects.