2.7 billion tons! Underwater ice loss in Himalayan glacial lakes is underestimated

With global warming, what is the loss of underwater ice in the Himalayan glacial lakes?

On the evening of April 3, Nature Earth Sciences published online a new research result by the second Qinghai-Tibet scientific expedition “Dynamic Change and Influence of Water Towers in Asia” and Zhang Guoqing, researcher of the environmental change and multi-circle process team of the Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences, showing that the mass loss of about 2.7 billion tons of underwater ice in the Himalayas from 2000 to 2020 was underestimated.

Zhang Guoqing, first author and co-corresponding author of the paper, said that digital elevation models (DEMs) are widely used to estimate global glacier mass loss. However, this method can only observe the surface and water surface of glaciers, and cannot reveal the loss of glacier mass that occurs below the water surface of preglacial lakes.

The Himalayan region is dotted with tens of thousands of glacial lakes. In the context of global warming, glaciers are retreating and retreating at an accelerated rate. Preglacial lakes connected to glaciers are expanding rapidly, accounting for about 12% of the total number of glacial lakes in the region. Previous studies have focused more on changes in the size and volume of glacial lakes and the resulting risk of glacial lake outburst flooding. However, when estimating changes in glacier ice quantity, traditional geodesy methods do not take into account the loss of underwater ice mass caused by the expansion of glacial lakes, resulting in underestimation of glacier mass loss in the Himalayan region and even on a global scale.

As a key member of the Key Laboratory of Earth System and Resources and Environment of the Qinghai-Tibet Plateau, Zhang Guoqing and others, together with researchers from Graz University of Technology in Austria, St. Andrews University in the United Kingdom and Carnegie Mellon University in the United States, used the remote sensing data of glacial lakes in multiple years to map and classify glacial lakes in the Himalayan region in detail, combined with the underwater topographic measurement data of typical glacial lakes, estimated the water volume changes of Himalayan glacial lakes in detail, and quantified the glacier mass loss under the surface of glacial lakes caused by climate warming.

The findings show that between 2000 and 2020, the number of glacial lakes in the Himalayas increased by about 47%, the area expanded by 33%, and the water volume increased by 42%. The increase in the volume of glacial lakes led to an underestimation of about 2.7 billion tons of underwater ice mass loss in the Himalayas between 2000 and 2020, accounting for about 6.5% of the total mass loss in preglacial lakes, with the Central Himalayan region being the most underestimated, about 1.2 billion tons, accounting for 10%. Located in the Poqu River basin in the central Himalayas, Galonco covers an area of about 5 square kilometers, with a maximum depth of 200 meters and a loss of 65% of underwater ice mass. At the same time, the study also preliminarily estimated the global loss of underwater ice in preglacial lakes, which is about 210 billion tons, accounting for 12% of the global total glacial lake contact glacier mass loss.

As glacial lakes in the Himalayas become larger and deeper, underwater ice loss remains an important factor influencing future total glacier mass loss and associated glacial lake outburst flood risk assessment. This study provides a method to quantify the mass loss of underwater ice, reduces the uncertainty of estimating the total mass loss of glaciers, provides important data for glaciological models, and provides an important scientific basis for more accurate simulation of past and future glacier mass balance, and assessment of glacier and glacial lake disasters and water resource changes. (Source: China Science News, Han Yangmei, Liu Xiaoqian)

Related paper information:

Schematic diagram of the estimation of underwater ice mass loss. Photo courtesy of the Institute of Tibetan Studies, Chinese Academy of Sciences

Underestimation of Himalayan underwater ice mass loss in 2000~2020. Photo courtesy of the Institute of Tibetan Studies, Chinese Academy of Sciences

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