Scientists say the growing concentration of rainfall into intense downpours — separated by longer dry stretches — may actually leave soils and ecosystems with less moisture over time.
The findings, published this month in the journal Nature, point to another way climate change may be reshaping water availability across the region.
Researchers analyzed decades of precipitation and land moisture data from around the world. They found that when rainfall becomes concentrated into heavier bursts, more water remains on the surface instead of soaking into soils or groundwater.
That leaves the water more vulnerable to evaporation.
“You’re really just not giving the land enough time to drink its fill when you have the water coming all at once,” said Justin Mankin, a climate scientist at Dartmouth College and co-author of the study.
Co-author Corey Lesk, a climate scientist at the University of Quebec in Montreal, described the process another way.
"You’re asking the land to drink from a firehose," Lesk said. “When water arrives on the land in really intense bursts, it can only absorb so much — there are limits on that. Soils are like a sponge, and they’re only so spongey.”
The study found some of the strongest trends toward rainfall arriving in fewer, heavier bursts — separated by longer dry stretches — in parts of the American West and the Amazon.
For Western states already grappling with drought, shrinking reservoirs and worsening wildfire seasons, the findings could complicate how water managers think about future planning.
Mankin said the shift creates a difficult balancing act.
Communities may increasingly have to manage flood risks from stronger storms while also preparing for longer and potentially more severe droughts later in the year.
The findings also raise questions about wildfire danger.
Dry soils and vegetation can help prime landscapes for fire, even in years with periods of heavy rain. Mankin said intense storms may not provide the same long-lasting moisture benefits as slower, steadier precipitation events.
Researchers emphasized that the work does not mean every large storm worsens drought conditions. Instead, they say the broader long-term pattern of rainfall arriving in fewer, more intense bursts appears to reduce how efficiently landscapes store water.
The research also underscores the growing complexity of climate change in the West, where communities already face rapid swings between extremely wet and extremely dry years.
Scientists say more research is needed to understand how changing rainfall patterns will affect agriculture, forests and water systems in the decades ahead.
This story was produced by the Mountain West News Bureau, a collaboration between KUNR, Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio, KJZZ in Arizona and NPR, with additional support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
