Rodell and study co-author Bailing Li, an assistant research scientist at UMD’s Earth System Science Interdisciplinary Center, studied 1,056 extreme wet and dry events. The satellites use precise measurements of Earth’s gravity field to detect water storage anomalies—specifically, how the amount of water stored in soils, aquifers, lakes, rivers, snow cover and ice compares to normal.

“It’s like watching the level of the water in your bathtub,” Rodell said. “You can see how much it rises and falls without knowing the total amount of water in the tub.” GRACE and GRACE-FO produce a new map of water storage anomalies around the world every month, providing a comprehensive view of the severity of hydrological events and how they evolve over time.

In their study, Rodell and Li applied an “intensity” metric that accounts for the severity, duration and spatial extent of droughts and extreme wet events. They found the global total intensity of extreme events increased from 2002 to 2021, mirroring Earth’s rising temperatures over the same period.

By far the most intense event identified in the study was a pluvial that began in 2019 in central Africa and is still ongoing, and which caused the level of Lake Victoria to rise by more than one meter. A 2015-16 drought in Brazil was the most intense dry event of the past two decades, leading to empty reservoirs and water rationing across some Brazilian cities.

“Both events were associated with climate variability, but the Brazilian drought occurred in the warmest year on record (2016), reflecting the impact of global warming,” said Bailing Li, a hydrologist. “The recent southwestern U.S. and southern Europe droughts were also some of the most intense events, in part due to anthropogenic warming.

“Global warming has had broad and profound impacts on terrestrial water storage, such as reduction of annual snow in high elevations and depletion of groundwater by people when surface waters are scarce,” Li added. “Reflecting these changes, GRACE data provide us a unique perspective of how hydrological extremes have been changing around the world.”

This article was adapted from a news release from NASA Goddard Space Flight Center.