According to one study, the world is receiving more rainfall overall, but it is also becoming drier. The confusing findings reveal a big problem.
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Another one for the weird science files.
New research shows that while the world is receiving more rainfall overall, it is also becoming drier.
How could that be? Simply put, global rainfall is becoming increasingly concentrated in larger storms, with longer dry seasons in between. And when too much rain falls at once, the soil becomes swollen and problems arise.
According to the findings, the study is the first to demonstrate that concentrating a year’s worth of rainfall into larger, wetter storms means less water is flowing into aquifers and ecosystems, even if total precipitation increases. There is a limit to the amount of water that soil can absorb at one time, so unabsorbed water collects on the surface where it evaporates more easily.
Study lead author Corey Lesk, a fellow at Dartmouth College who led the study, explained in an email to USA TODAY: “Irrespective of the amount of precipitation, stronger rainfall and snowfall, interspersed with longer dry periods, tend to leave less water on land (soil, lakes, groundwater) available for use by humans and nature.”
“Ask the land to drink water from the fire hose.”
In a new study published May 13 in the British peer-reviewed journal Nature, researchers analyzed global rainfall records from 1980 to 2022 and determined that annual rainfall is more concentrated regardless of whether the local climate is wet or dry.
“We found that it’s not just the quantity that’s delivered that matters, but also the way it’s delivered,” Justin Mankin, the study’s lead author and associate professor of geography at Dartmouth College, said in a statement. “Rainfall concentration is essentially asking the land to drink from the firehose. Heavy rainfall often leads to dry days, but more importantly, heavy rainfall creates ponds on the ground that are more easily evaporated by the atmosphere,” he added.
“It doesn’t matter where you are, the more rainfall you have, the less water is available to your land,” Mankin said.
Is climate change to blame?
Researchers say that’s likely the cause.
“We haven’t specifically tested the extent to which recent trends in concentrated precipitation are driven by climate change,” Lesk told USA TODAY. “But they are consistent with what we would expect from theory about how warming will shape the temporal distribution of rainfall.”
“We show that warming is a driver of dryness, regardless of whether total future precipitation increases or decreases,” he added.
Looking to the future, the study predicts that as global temperatures rise due to climate change, rainfall will become more concentrated. A rise of 3.6 degrees Celsius could make land abnormally dry for 27% of the world’s population, potentially offsetting increases in total precipitation, researchers report in a study.
“This is not a positive effect that we found,” said Lesque, now a professor of earth and atmospheric sciences at the University of Quebec in Montreal. “This sheds light on how climate change impacts water resources for everyone.”
“As the rainfall becomes more concentrated under global warming, the surface will become drier,” Mankin said. “What remains unresolved is whether future changes in total precipitation can maintain this pace.”
Challenges for water resource managers
Mankin said in a statement that erratic boom-and-bust cycles of heavy rains and prolonged droughts complicate the management of public water supplies, especially in arid regions where water storage is critical.
“This adds an additional challenge to managing water resources, but the good news is that once we understand this concentration effect, we can better incorporate it into things like water management and drought prediction,” Lesk told USA TODAY in an email.
“Rainfall concentration is typically not included in these assessments because its importance was not previously understood,” he said.
Mankin said the study presents a new way of thinking about water resources, showing that how much rain falls each year and when it falls is just as important as how much rain falls each year. Climate scientists predict that a warmer climate will lead to more rainfall, but they are not sure if that means more water on the land, he added.
Western US Warning
The study found that the United States west of the Mississippi River experienced some of the world’s highest concentrations of rain, with annual rainfall in the Rocky Mountains increasing by 20% and becoming more intense.
Mankin said California has recently faced this problem as atmospheric rivers flooded the state during a prolonged drought. Water managers must decide whether to free up valuable reservoirs to collect new rainwater, but it’s unclear how long the new supply will last.
