The world’s largest lakes are shrinking dramatically, and scientists say they have figured out why

More than half of the world’s largest lakes and reservoirs have lost significant amounts of water over the last three decades, according to a new study, which pins the blame largely on climate change and excessive water use. Roughly one-quarter of the world’s population lives in the basin of a drying lake, according to the study by a team of international scientists, published Thursday in the journal Science.

While lakes cover only around 3% of the planet, they hold nearly 90% of its liquid surface freshwater and are essential sources of drinking water, irrigation and power, and they provide vital habitats for animals and plants. However, they are in trouble Lake water levels fluctuate in response to natural climate variations in rain and snowfall, but they are increasingly affected by human actions.

More than half of the net loss of water volume in natural lakes can be attributed to human activities and climate change, the report found. The report found losses in lake water storage everywhere, including in the humid tropics and the cold Arctic. This suggests “drying trends worldwide are more extensive than previously thought,” Yao said.

In the Arctic, lakes have been shrinking due to a combination of changes in temperature, precipitation, evaporation and runoff. Climate change can have an array of impacts on lakes. The most obvious, Yao said, is to increase evaporation.

As lakes shrink, this can also contribute to an “aridification” of the surrounding watershed, the study found, which in turn increases evaporation and accelerates their decline. For lakes in colder parts of the world, winter evaporation is an increasing problem as warmer temperatures melt the ice that usually covers them, leaving the water exposed to the atmosphere.

These changes can have cascading effects, including a decrease in water quality, an increase in toxic algal blooms and a loss of aquatic life. Lake Powell, for instance the second-largest human-made reservoir in the US has lost nearly 7% of its storage capacity due to sediment build-up. Sedimentation can be affected by climate change, he added. Wildfires, for example, which are becoming more intense as the world warms, burn through forests and destabilize the soil, helping to increase the flow of sediment into lakes and reservoirs.

Some lakes have been growing, with 24% seeing significant increases in water storage. These tended to be lakes in less populated regions, the report found, including areas in the Northern Great Plains of North America and the inner Tibetan Plateau. The fingerprints of climate change are on some of these gains, as melting glaciers fill lakes, posing potential risks to people living downstream from them. This new research provides a useful long term data set that helps untangle the relative importance of the factors driving the decline of lakes.