They can be shallow or deep. Sparkling and quiet. Even mysterious and deadly. Approximately 5 million square kilometers of the earth’s surface are covered by natural and artificial lakes. And these abound in unique life. But something is about to happen. And the changes are happening at an alarming rate, a new study shows. Because in addition to the world’s lakes struggling with the rise of algae, as well as the loss of oxygen, they also face another major challenge: Fresh water evaporates at a faster rate than first thought. A thirsty sky Researchers at the University of Texas are behind the new study. In total, they have analyzed as many as 1.4 million lakes worldwide. Among other things, they have used satellite images that show monthly water loss in the years between 1985–2018. The researchers have taken into account several things, including evaporation rate, surface area and changes in heat storage. They have done this in every single lake. The results show that the lakes in total evaporate 15.4 percent more water than previous estimates have shown, explains ecologist Gang Zhao. He says the sky is “thirstier” than ever. This picture shows the dehydrated Lake Aculeo in Chile. For several years, this was one of the biggest tourist attractions in the area around Santiago. Photo: MARTIN BERNETTI / AFP Evaporates more than we use Higher temperatures and increased radiation from the sun means that the sky swallows up water molecules like never before. These are then dispersed into the atmosphere. Previous estimates are based on the evaporation rate, but they have not taken into account the large volume of water that is lost. This may be due to water that both freezes and thaws, the researcher explains. “In order to achieve a reliable target, therefore, evaporation must be calculated independently for each lake,” says Zhao. And that is exactly what he and his colleagues have now done. In a global perspective, the total evaporation may be greater than the combined use of water in households and industry, the researchers believe. Now they hope the results can contribute to a better understanding, and that everyone who works with this can use the new dataset they have developed. – One can better understand the role these water bodies play in different systems. This can be anything from global weather forecasting to flood and drought modeling during climate change, says Zhao. This overview shows the percentage volume of lake evaporation (VE) versus total evaporation volume (VET) in the period 2001 to 2018. Photo: Texas A&M University College of Engineering Is concerned Anne Lyche Solheim is chief researcher at the Norwegian Institute for Water Research (NIVA). She says increased evaporation in arid areas of the world presents a number of challenges. – It will reduce the water volume in the lakes and make them more vulnerable to pollution. This can create problems for water supply to agriculture and the population. Especially in developing countries, she tells news. Such problems can also occur in northern latitudes this year with little precipitation, but then to a lesser extent. It is pollution that worries her the most. – We are concerned about the development. Climate change, with a combination of warmer water and the change between droughts with low water levels and torrential rain, could exacerbate the effects of pollution. It can also adversely affect biodiversity. – Heavy rain could increase the supply of nutrients from agriculture and overflows in sewage treatment plants. It will require comprehensive measures to counteract this, says Solheim. The new study is published in Nature Communications. This picture shows algae blooms in Lake Mjøsa. This is something lakes all over the world struggle with. Photo: Bjørnar Fjeldberg / NTB scanpix
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Lakes around the world are drained of water much faster than expected – news Trøndelag
