BEIJING, May 21 (Reporter Sun Zifa) In the context of global warming, what characteristics and change patterns will appear in global ice lakes and outburst flood areas?
The latest research estimate, led by researcher Zhang Guoqing from the Environmental Change and Multilayer Process Team of the Qinghai Tibet Plateau Research Institute of the Chinese Academy of Sciences and jointly completed by scientists from Britain, Austria, Canada, Switzerland, Germany and other countries, shows that the risk of global glacial lake outburst floods will generally increase in the future, but there are regional differences.
The international cooperation team built a comprehensive global ice lake dataset by comprehensively analyzing the ice lake and historical ice lake outburst flood events of different sizes and types in the world and regions, elaborating the distribution status, regional characteristics and change mode of global ice lakes, quantifying the proportion and historical occurrence trend of different types of ice lake outburst floods in the world, The disaster risks and countermeasures of future global ice lakes and ice lake outburst floods are estimated. Relevant achievement papers were published online in the international professional academic journal Nature Earth Environment Review on May 21.
Researcher Zhang Guoqing, the co first author and corresponding author of the paper, said that under the background of global warming, glaciers are melting and retreating at an accelerated rate. When the glacial melt water is blocked by glaciers, moraines or bedrock, ice lakes are formed in front of the ice, on the edge of the ice, on the ice surface, in the ice or under the ice. Ice lake may cause ice lake burst flood. It is very important to carry out a comprehensive study on the geographical distribution, formation time, evolution process and physical characteristics of global ice lakes to mitigate the damage caused by ice lake outburst floods in the downstream area. In the past, studies on ice lakes were single and scattered, or focused on specific types of ice lakes or only on specific mountain areas, lacking research on the characteristics and changes of global system ice lakes and ice lake outburst floods.
Relevant research shows that there are 22133 ice lakes with an area of more than 0.05 square kilometers, with a total area of about 14438 square kilometers. The number, area and volume of global ice lakes vary significantly in different regions. Ice lakes are mainly distributed at the edge of Greenland (31%), the South Andes (16%), Alaska and western Canada (16%), the eastern Canadian Arctic (15%) and the Asian alpine region (6%). A comprehensive and thorough understanding of the geographical characteristics of ice lakes is a prerequisite for the risk assessment of ice lake outburst floods. The changes of ice lakes in most mountain areas around the world show the following characteristics: relatively stable from 1850 to 1970, gradually expanding from 1970 to 1990, and rapidly expanding from 1990 to 2020. The changes of ice lakes in the Andes, central Europe and Svalbard Islands are relatively small, with the change amplitude less than 10% every decade; Iceland, Scandinavia and the Russian Arctic have relatively large changes, with a change rate of more than 40% every decade.
In this study, the international cooperation team further comprehensively analyzed the distribution, causes and mechanisms of historical ice lake outburst floods, and found that ice dam and lake are the most important type of ice lake outburst floods, accounting for two-thirds of all recorded events in the world. In the regional scope, Alaska is the hot spot of ice dam lake ice lake outburst floods, accounting for 37% of the global total. The break of ice dam and lake may occur repeatedly, because the ice dam may temporarily "heal" after the lake water is discharged.
Moraine lake is also the source of common glacial lake outburst flood, especially in the Andes Mountains, central Asia and Himalayas at low latitudes. Their collapse is usually triggered by piping, buried ice degradation or overflow caused by ice avalanches, avalanches or landslides. Unlike ice dam lakes, moraine lakes usually break only once, because the destruction of the dam body limits the ability to store water in the future. In addition, the study also mentioned that the status of bedrock dams is generally stable, and these ice lakes generate less ice lake break floods than ice dam lakes and moraine lakes. Overflow dam is the only mechanism for the occurrence of ice lake break floods.
Zhang Guoqing pointed out that due to the limited available satellite image data, the record of ice lake outburst floods before 1980 was less than the actual, and the reported increase trend of ice lake outburst floods would be biased. With the further melting and retreat of glaciers, existing ice lakes expand and new ice lakes appear. In Asia's alpine regions, under the scenario of complete disappearance of glaciers, about 13000 ice lakes with a total area of about 1510 square kilometers and a total volume of about 52.3 cubic kilometers may be formed.
The prediction results of this study show that the risk of future global ice lake outburst floods will generally increase, but there are regional differences. The future ice lake outburst floods in Asia's alpine regions are expected to increase, while the potential ice lake outburst floods in Western Europe's Alps and Peru's Cordillera Branca Mountains are relatively low. Iceland may have volcanic activities in the future, which may lead to large-scale ice lake outburst floods.
Zhang Guoqing said that the international cooperation team also comprehensively studied the geographical distribution, change characteristics, causes and mechanisms and future trends of global ice lakes and historical ice lake outburst floods, and proposed future research directions, including new technologies and methods for ice lake monitoring and risk assessment, global complete ice lake cataloguing and acquisition of field observation data, and improvement of flood dynamic model, It provides scientific basis and policy recommendations for the global response to ice lake related disaster risks. (End)
