The study concludes that the lakes studied over a 30-year period drained the equivalent of the entire water consumption of the United States in 2015.
The amount of water is decreasing in more than half of the world’s lakes and reservoirs, threatening a vital source of fresh water, according to a study, published Thursday, May 18, which largely attributes this trend to global warming and their excessive use by humans.
About a quarter of the world’s population lives in an area with a drying lake or reservoir, warns this study published in the prestigious journal Science. The lakes, which “enable societies and humanity to live” are “endangered globally, and this has far-reaching implications”, said Balaji Rajagopalan, a professor at the University of Colorado Boulder, and co-author of the study. Lakes cover about 3% of the earth’s surface, but account for 87% of liquid fresh water on Earth. They are used for human consumption, agriculture, or even the production of electricity.
The human activities involved
Previous work has already looked at the decline of larger lakes individually. But this study is the first to offer a detailed view of global trends, and the causes of the observed changes, thanks to satellite observations. In total, the researchers studied 1,972 bodies of water, representing the vast majority of natural lakes (focusing on those larger than 100 km2) and reservoirs. Over the almost 30-year period studied (from 1992 to 2020), the study concludes that they have emptied the equivalent of all the water consumption of the United States in 2015.
The study has an unexpected result: lakes lose water not only in arid areas, but also in humid regions. For natural lakes, scientists attribute about half of water loss to human activities and rising temperatures, which cause increased evaporation, the latter factor being linked to climate change.
But another important factor, namely the lack of precipitation, “can also be attributed to climate change in some places”, notes Balaji Rajagopalan. In addition, humans or herds may need to consume more water due to higher temperatures. “Clearly, the footprint of climate change is already there”notes the researcher.