Millions of people rely on water from High-Mountain Asia’s glaciers. South-eastern Tibet, on the other hand, has some of Asia’s fastest melting glaciers. According to a study led by the Swiss Federal Institute for Forest, Snow, and Landscape Research WSL, this is due to less summer snowfall.
Unlike in the Alps, the Tibetan Plateau’s glaciers receive the majority of their snowfall during the summer months, which are the wettest but also the warmest. The glaciers of the south-eastern Tibetan Plateau feed the Brahmaputra River, which provides domestic, agricultural, and industrial water to millions of people downstream.
Earth-observation satellites have recently revealed that glaciers in this region are losing mass at some of the fastest rates in Asia, and this loss has been accelerating in recent decades. We know that rising temperature caused by climate change cause glaciers to melt, but is this the only factor contributing to the rapid retreat of glaciers in this region?
No, according to research led by Achille Jouberton and Francesca Pellicciotti of WSL in collaboration with the Chinese Academy of Sciences’ Institute of Tibetan Plateau Research. The researchers have uncovered the mechanisms underlying the glaciers’ high sensitivity to warming in south-eastern Tibet.
Modeling 45 years of change
They used a cutting-edge model to reconstruct the climate and mass changes of the Parlung No.4 glacier in south-eastern Tibet over the last 45 years in order to identify these mechanisms. That is the longest time span for which changes in a glacier in this region have been reconstructed. The scientists’ so-called glacio-hydrological model was informed by a large set of data collected on-site and via remote sensing. Glacio-hydrological models combine glaciological and hydrological processes, such as glacier and stream flow.
Long-term changes in precipitation phase are difficult to detect, particularly at high elevations in glacier accumulation areas. They necessitate continuous precipitation measurements, which are frequently expensive and fraught with uncertainty. As a result, the most practical way to quantify them was to use a well-informed model calibrated with locally collected data.
Summer rain instead of snow
The researchers discovered that the majority of the mass loss acceleration was caused by a shift in some of the summer precipitation from snow to rain, limiting the accumulation of snow on the glaciers, which eventually turns to ice. Their findings show that glacier melt has increased as well, but that the decrease in snow accumulation was a more significant cause of recent mass loss in this region.
Because less snow accumulates on glaciers, glacier ice is exposed to sun and warmth for a longer period of time during melt seasons, which can greatly enhance melt. This has also been seen this summer in the Alps, where a small winter accumulation has resulted in early and excessive summer melt.
Overall, the findings emphasise the importance of accounting for changes in glacier accumulation mechanisms in glacier change projections, and they help to explain the particular sensitivity of summer-accumulation glaciers to warming.
The findings were reported in the Proceedings of the National Academy of Sciences.