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Something weird and worrying is happening with rain, study finds
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Another one for the weird science file. New research shows that although the world is seeing more rain overall, it's also getting drier at the same time. How can that be? In simple terms, the world's rainfall is increasingly packed into bigger storms with longer dry spells in between. And a lot of rain all at once causes problems for overwhelmed soil. The findings say the study is the first to demonstrate that a year's worth of rainfall packed into bigger and wetter storms means less water for aquifers and ecosystems, even if total precipitation increases. Because soil can absorb only so much water at once, what is not soaked up collects on the surface where it's more readily evaporated. Study lead author Corey Lesk, who led the study while a fellow at Dartmouth College, explained it in an email to USA TODAY: "Regardless of how much precipitation falls, when rain and snow come in stronger bursts separated by longer dry spells, less water tends to remain on the land (in soils, lakes, and groundwater) for use by people and nature." Researchers analyzed global precipitation records from 1980 to 2022 and determined that annual rainfall has become more concentrated regardless of whether the local climate is wet or dry, according to the new study published May 13 in the peer-reviewed British journal Nature. "We discovered that it's not just supply that counts, but also how it's delivered," said Justin Mankin, the study's senior author and an associate professor of geography at Dartmouth, in a statement. "Rainfall concentration is essentially asking the land to drink from a firehose. When rainfall is intense, you get more consecutive dry days, but more important is that heavier rains lead to surface ponding that is more easily evaporated by the atmosphere," he added. Climate news: People haven't just made the planet hotter. We've changed the way it rains. "It doesn't matter where you are, more consolidated rainfall means less water is available for the land," Mankin said. Researchers say it's a likely cause. "We did not specifically test to what extent recent trends towards more concentrated precipitation are caused by climate change," Lesk told USA TODAY. "But they are consistent with what we would expect from the theory of how warming shapes how rainfall is distributed in time." "We show that warming weighs the dice for drying, regardless of whether total precipitation increases or decreases in the future," he added. Looking ahead, the study projects that rainfall will grow more consolidated as global temperatures rise due to climate change. An increase of 3.6 degrees could lead to abnormally dry land conditions for 27% of the world's population, offsetting any rise in total rainfall, the researchers report in the study. "This is not a good effect we've uncovered," says Lesk, who is now a professor of Earth and atmospheric sciences at the University of Quebec in Montreal. "It really exposes the mechanics of how climate change will affect water resources for everyone." "Consolidation of rainfall under global warming will lead to a drier land surface," Mankin said. "What is unresolved is whether future total precipitation changes can keep apace." An erratic boom-bust cycle of heavy rainfall and long droughts will complicate the management of public water supplies, Mankin said in a statement, especially in arid regions where water storage is critical. Lesk told USA TODAY via email that "this adds a layer of challenge to managing water resources — but the good news is that if we understand this concentration effect, we can incorporate it better into water management, drought forecasting, etc." "Rainfall concentration is not typically included in those assessments, largely because its importance wasn't understood until now," he said. The study presents a new way of thinking about water resources by showing that how and when rain falls during the year is as important as how much falls all year, Mankin said. Climate scientists project that a warmer climate will result in more rain, but it's been less certain if that means more water for the land, he added. According to the study, the United States west of the Mississippi River experienced some of the world's highest levels of rain consolidation, with yearly rainfall for the Rocky Mountains becoming 20% more compacted into heavier downpours. California has faced this issue recently during long-term droughts when atmospheric rivers have drenched the state, Mankin said. Water managers must decide whether to release precious reservoirs of water to collect freshly fallen rainwater with no certainty of how long the new supply will last. This article originally appeared on USA TODAY: Rainfall patterns are acting weird, and it's a big problem, study says