Environment

A disturbing process has been accelerating in freshwater lakes worldwide, study finds

On top of intensifying algal blooms and depleting oxygen, a new study reveals Earth’s bodies of freshwater are also evaporating at a greater rate than we realized.

What’s more, “lake evaporation plays a larger role in the hydrological cycle than previously thought,” says ecologist Gang Zhao who was at Texas A&M University during the study. This process thus has a substantial impact on our climate and weather modeling.

With their shimmering waters, natural and artificial lakes adorn around 5 million square kilometers of Earth’s terrestrial surface. They contain almost 90 percent of our planet’s fresh liquid surface water and overflow with often unique life.

But warming temperatures and increased solar radiation due to changes in cloud cover have made the sky thirstier than ever. Larger areas of exposed water due to a decrease in ice cover have also given the sky greater access to slurp up those water molecules. These factors all contribute to an increasingly rapid cycling of water from its pooling on land to its dispersal into the atmosphere.

Previous estimates of this water transfer relied on evaporation rates, but these alone fall short of representing the sheer volume of lake water being lost, due to other dynamics like freeze and thaw cycles. Because of this dependence on localized environmental conditions, a reliable measure of evaporation has to be calculated independently for each lake.

So Zhao and colleagues did just that for a staggering 1.42 million lakes worldwide. They used monthly water loss information from satellites between 1985 to 2018 and factored in the evaporation rate, surface area, ice duration and heat storage changes for each of these lakes.

“We found that the long-term lake evaporation is 1,500 plus or minus 150 cubic kilometers per year, which is 15.4 percent larger than previous estimates,” says Zhao.

And the sky is drinking over 3 trillion liters more than previously each year. The researchers also found artificial reservoirs have a proportionally larger contribution to this evaporation (16 percent) than their storage capacity of 5 percent would suggest.

“From a global perspective, the total reservoir evaporation can be larger than the combined use of domestic and industrial water,” explains environmental engineer Huilin Gao.

“However, even in the United States, very few lakes/reservoirs have reliable evaporation data.”

Zhao and team made the dataset they created, the global lake evaporation volume (GLEV), publicly available and urge those making water management decisions and the wider scientific community to make use of it.

“With results for individual water bodies, GLEV can really help improve reservoir management decision-making all over the world, especially under increasing drought events and population growth,” says Gao.

“This dataset helps the science community better understand the role that these water bodies play in Earth systems, from global weather forecasting, flood and drought modeling to Earth system modeling under climate change.”

This research was published in Nature Communications.

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