Cryospheric change and its impact on water resources
Most of the world’s glaciers are melting at an accelerated rate worldwide: Global warming is reducing snow accumulation and snow cover duration, accelerating glacier mass loss and retreat, causing permafrost (permanently frozen ground) thaw and prompting more extreme rainfall events and natural hazards.
The mountain cryosphere is one of the components of the Earth system that is most sensitive to global climate change. The following illustration shows key cryosphere and hydrological changes due to global warming in high mountain regions in the 21st century.
Glaciers have been melting rapidly since the 20th century
The retreat loss of glaciers have been ongoing since the 20th century in most parts of the world and have accelerated in recent decades. With global warming of between 1.5°C and 4°C, mountain glaciers worldwide are projected to lose 26% to 41% of their total mass by 2100. A great number of individual glaciers will disappear entirely, leaving many currently glacieted mountain headwaters unglaciated. Dust, combustion-related soot deposits including black carbon, and microbial and algal growth on snow and glaciers are becoming more common due to the increased frequency of dust storms, air pollution and wildfires and they can accelerate melt rates by decreasing surface albedo until the next snowfall.
The consequences of climate change, including higher temperatures, glacial recession, permafrost thaw and changing precipitation patterns, can affect flood and landslide risks. Landslides and avalanches can block and damage transport infrastructure and cause devastation to human settlements and activities. Geohazard events are being observed in mountain regions globally and it has been calculated that the absolute economic losses in mountain regions across 713 events between 1985 and 2014 exceeded US$56 billion, affected over 258 million people and resulted in over 39,000 deaths.
With a warming climate, mountain regions globally are receiving emissions from an increasing number of wildfires and dust storms. Together with human activities, these are leading to growing deposition of black carbon and other particulate matter on glacier surfaces and perennial snowpacks. The impurities darken snow and ice surfaces, thus causing greater absorption of solar radiation. This can increase melt rates, especially during periods and at locations of high solar radiation.
Mountains and glaciers’ key role
High mountains are responsible for generating large amounts of runoff and streamflow, and about 2 billion people depend on them for their freshwater supply.
They form the headwaters of many rivers around the world and play a major role in the global hydrological cycle: cyclical warm season melting of mountain snowpacks and glaciers releases fresh water, which can flow directly into streams and rivers or percolate into the ground, replenishing soil moisture and groundwater. Changes in the timing and volume of peak and low flow periods, increased erosion and sediment loads will affect water resources downstream, in terms of quantity, timing and quality.
Communities in the Cordillera Blanca of Peru have long been managing glacial lake outburst floods (GLOF). Rockfalls, land slides and glaciers calving into water bodies have triggered events with devastating impacts. These have resulted in substantial engineering mitigation efforts to mitigate GLOF occurrences, including lowering of lake levels and reinforcing moraine dams to prevent erosion and failure. There are now drainage pipes and tunnels, artificial dams and early warning systems across multiple lakes throughout the Andes (Mergili et al., 2020). These include drainage pipes leading away from Lake Palcacocha, which, in 1941, was the source of a GLOF that killed an estimated 1,600 people.
Full chapter
Consult chapter 2: Changes in the cryosphere and impacts on water.
