Research reveals smaller glacial lakes more prone to flooding

For many years, scientists have been discussing whether the population in mountain regions is increasingly at risk from meltwater floods, as melting glaciers release more and more water. A small proportion of this meltwater remains in the glacial lakes around the world. If their dams break, the corresponding glacial lake floods can have catastrophic consequences for the population living downstream. The Potsdam research team was able to show that it is not only the increasing number and surface area of glacial lakes that determines the risk of such floods. By analyzing satellite images of almost 1700 documented glacial lake floods in 13 glacier regions around the world over a period from 1990 to 2023 they found that the areas of ice dammed lakes became smaller, while those of moraine-dammed lakes remained largely constant. Overall, they were unable to identify a trend towards larger lake floods.

“Some lakes have developed a wide outlet over time. This allows the rivers from these lakes to discharge the meltwater very efficiently without necessarily breaking the dam. Other lakes, especially in the Alps, Peru and Norway, have been artificially reinforced with dams in order to use them intensively for hydropower”, says leading author Dr. Georg Veh from the Institute of Environmental Science and Geography. Such lake changes contribute to the fact that floods tend to originate from smaller lakes, even if lake areas are increasing globally.

Not all lake floodings behave in the same way. Glacial lakes that are held back by glacier ice do break out more frequently due to increasingly unstable ice masses. However, the resulting flood events are on average less massive due to the smaller lake volumes. Other lakes are dammed by moraines left behind by glacial melting. In the Himalayas, Alaska and Patagonia in particular, the potential danger posed by moraine-dammed lakes for settlements and infrastructure downstream has increased as their volume continues to grow. However, catastrophic flooding by moraine-dammed lakes, such as in India in 2023 with at least 55 fatalities, remain rare.

The authors emphasize how closely climate change, glacier retreat and natural hazards are linked—and how important it is to continuously monitor these processes. “Remote sensing plays a key role here. It allows us to monitor processes in places that would otherwise be inaccessible, across a wide area and at low cost. At our institute, we use daily high-resolution satellite images to better monitor the growth of glacial lakes“, says Dr. Veh. The real-time data provides a valuable basis for risk management in mountainous regions. Therefore, future measures to protect people, roads and power plants can be better planned on site.

The paper is published in the journal Nature Water.