California’s Rain Turns Heavier, Dry Spells Lengthen

A new study finds rainfall is concentrating into heavier storms, leaving longer dry gaps that dry out California and the West.

Heavier storms followed by longer dry spells are leaving California and much of the West drier than many people expect—because it’s not just how much rain falls, but how it arrives.

Across much of California and the broader western United States. researchers found that rainfall has become more clustered into heavier events. with longer stretches in between.. The net effect. the study says. is a drying of the landscape: even when precipitation totals do not necessarily rise in step with expectations. the timing and intensity of downpours can change how much water the land can actually use.

The research is presented as the first effort to directly map how concentrating rainfall into fewer. heavier episodes can dry out environments.. In interviews connected to the study. geography professor Justin Mankin described the underlying mechanism as a limit of absorption: when rain arrives in intense bursts. the soil and ground cover can’t take it in quickly enough.. “The more concentrated rainfall you get. the drier you become. ” Mankin said. likening it to asking land to drink from a fire hose.

In the explanation offered by the authors, a key part of the problem is what happens after heavy downpours.. When precipitation becomes more intense. more water can end up sitting on the surface rather than soaking in. making it easier for that moisture to evaporate.. This matters for ecosystems and for human water supply alike. because it shifts rainfall away from the slow processes—like infiltration and replenishing groundwater—that support regions through dry periods.

While the overall pattern shows up across much of the West, the study notes that the trend is not uniform.. Researchers say the signal is less clear in Southern California and more pronounced in the North. suggesting the region’s geographic and climate differences can influence how strongly residents experience “rainfall consolidation” in practice.

The analysis. published Wednesday in the journal Nature. examined global precipitation patterns from 1980 to 2022 using satellite data that track shifts in water across landscapes.. The study focused on where precipitation has grown drier or wetter over time and what those changes look like in terms of clustering and intensity. rather than relying only on broad averages.

One of the findings with major implications for U.S.. water planning involves the Rocky Mountains.. The researchers reported that precipitation there has become about 20% more concentrated. a shift that can affect the Colorado River. a critical water source for California and other parts of the Southwest.. The Colorado River has shrunk dramatically since 2000. according to scientists. in what they describe as a megadrought likely among the most severe in 1. 200 years.

The study also connects the observed shifts to expectations about a warming climate.. Experts have long anticipated that global warming can produce precipitation that is less frequent but more intense. driven by a warmer atmosphere’s ability to hold more water vapor.. In this case. the authors argue that rainfall consolidation is already occurring across parts of the western U.S.. aligning with what climate change theories would predict.

“As more planet-warming gases are released from burning fossil fuels. ” the study’s discussion notes. rising heat does more than change rainfall patterns.. Higher temperatures increase evaporation from the land and can alter how much moisture plants absorb. intensifying the stress on soil and vegetation during longer dry intervals.

For California specifically, the report emphasizes that the state already experiences dramatic swings between drought and flood.. Climate models have projected an intensification of rain in the state—especially tied to atmospheric river storms—and the new findings add detail to what that can mean on the ground when precipitation falls in larger. more spaced-out bursts.

A research meteorologist not involved in the study. Alexander Gershunov of the Scripps Institution of Oceanography at UC San Diego. said the models suggest a regional split as temperatures rise: Southern California is likely to get a little drier. while Northern California is likely to get a little wetter.. He also pointed to another pressure on water storage—warmer temperatures shrinking the snowpack in the Sierra Nevada—meaning more of the state’s water may shift toward relying on big downpours during atmospheric rivers rather than gradual melt.

The study further argues that rainfall consolidation is occurring regardless of whether a region is currently wet or dry. suggesting the mechanism is not limited to places that are already arid.. That universality. researchers say. is part of why the pattern could matter for water resources more broadly. not just in California.

Corey Lesk. who led the study while at Dartmouth and is now a professor of Earth and atmospheric sciences at the University of Quebec in Montreal. said the trend of fewer but stronger storms “really exposes the mechanics of how climate change will affect water resources for everyone.” Other research previously found that large areas of the world are growing drier. including a “mega-drying” region stretching from the western U.S.. through Mexico to Central America.

The new report reframes how water availability should be understood.. Mankin said the amount of water a region can effectively get depends not only on the total precipitation. but also on how concentrated it becomes.. That distinction is crucial for places where the dry periods are lengthening. because even similar rainfall totals can translate into very different outcomes depending on how quickly water arrives.

For policymakers and agencies tasked with drought and flood management, the study’s implications are stark.. The authors and experts connected to the report say that in California and other western states. current approaches may not adequately account for a future in which rainfall comes in more consolidated bursts followed by longer dry spells.

“This is just another indicator … we are not adapted to the climate we have, let alone the one that seems to be unfolding,” Mankin said, underscoring the concern that water systems designed around earlier patterns may struggle as the timing and intensity of precipitation keep shifting.

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