Warming atmosphere fueling heavier U.S. rainfall and rising flood risk, AccuWeather analysis shows
A new AccuWeather study of more than 60 years of rainfall records shows U.S. precipitation totals are flat, but heavy downpours and hourly extremes are increasing, raising the risk of flooding, damage, and economic losses.
AccuWeather data analysis shows that the rate of intense rainfall has increased over the last couple decades leading to increased potential of extreme flooding in areas prone to high rain events.
It’s not raining more across the United States, but when it rains, it’s falling harder, faster and in more extreme bursts. That’s the finding of a new AccuWeather analysis of more than 60 years of weather records, which reveals a striking shift: National rainfall totals remain statistically flat, yet the number of heavy downpours and hours with extreme rainfall have increased sharply.
These changes are fueling greater flood risk, straining infrastructure and threatening communities nationwide.
(Getty images)
The data behind the story
AccuWeather Senior Vice President of Strategic Initiatives Steve Root says the findings were only possible because of the depth and quality of AccuWeather’s database, which normalizes rainfall across 44 U.S. climate zones. Each zone is anchored by a long-term, calibrated government station, ensuring wetter regions don’t drown out trends in drier ones.
“Our national composite of 44 climate zones across the contiguous U.S. shows no statistically significant upward trend in annual precipitation, year over year, while heavy-rainfall days and hourly extremes have increased since the mid-20th century,” Root said.
Brett Anderson, AccuWeather Senior Meteorologist and Climate Expert, added: “The intensity of rainfall is steadily increasing, especially in 2– to 4-inch amounts. The biggest increases have occurred over the past 20 to 30 years.”
Why totals don't tell the whole story
The first question Root tested was simple: Is it raining more overall? The answer: no.
“Annual precipitation remains statistically flat in our national composite; the shift is toward event intensification,” Root explained.
That shift matters, because flooding isn’t driven by how much rain falls in a year, it’s driven by how hard and how fast it comes down. A region can receive the same annual total, but if more of that water arrives in single-day downpours or hour-long cloudbursts, the risk of flash flooding rises dramatically. That’s when storm drains overflow, culverts back up and rivers breach their banks.
“Totals alone miss the risk. Intensity and local land use and drainage capacity drive flood outcomes,” Root said.
When it rains, it pours
By looking at daily thresholds from routine showers to extreme downpours and tallying how many hours per year brought more than an inch of rain, Root uncovered a consistent upward climb in rainfall intensity.
“The frequency of days with at least three-quarters of an inch of rain has increased by about 10% over the past 30 years, while national totals remain statistically flat,” Root said. “Daily rain events of 4 inches or more have roughly doubled since the 1960s; 3-inch-plus events show a strong upward trend. Hours per year with rainfall of one inch or more have approximately tripled since 1950.”
Anderson said the records bear that out. “We are constantly seeing records broken, much more often than in the past. It’s almost a yearly occurrence now.”
This intensification is consistent across the country but not at the same pace everywhere. Different regions are responding at different speeds because the atmosphere doesn’t warm or release moisture evenly. Weather systems shift, surge and stall, distributing rainfall in unpredictable ways.
“The atmosphere is not equally changing everywhere. Some areas are changing at different rates. It’s like a 4-inch fire hose that somebody turns on full blast. It’s gonna whip around and do different things and spray different areas differently, and that’s kind of what we’re seeing,” Root explained.
Warmer air, more moisture, heavier rain
Scientists know why this is happening: Warmer air can hold more moisture. That extra moisture fuels heavier downpours when storms form.
“A warmer atmosphere can hold more moisture. For every degree Celsius of warming, the atmosphere can hold about 7% more water vapor, increasing the potential for extreme rainfall,” Anderson said. “The climate has clearly changed over the past 10 to 20 years and will continue to become more extreme."
Flood risk isn't just about weather; it's about cities
While the U.S. isn’t wetter, it is stormier. “The U.S. is not measurably wetter at the national scale, but it’s becoming stormier and more volatile. That distinction matters for risk, engineering and preparedness,” Root said.
The problem is compounded by how we’ve built our communities. “Drainage systems, roads and neighborhoods face higher odds of being overwhelmed when similar annual totals arrive in shorter, more intense bursts,” Root noted. “Short, high-rate bursts overwhelm storm drains and culverts that were built for a different era of rainfall.”
Anderson agreed: “We have a lot of old plumbing that is costly to replace, and we’ve added a lot more pavement. Heavy rain now runs off pavement instead of soaking into soil, leading to more flooding.”
Impacts on agriculture and long-range patterns
The consequences extend beyond flooding streets. Heavier rains are also reshaping agriculture and long-term climate signals.
“The bigger challenge for farmers is extremes,” Anderson said. “Extreme rainfall can wash away soil, flood fields and delay planting for weeks. Some years are great; other years are terrible. The variability from year to year is increasing, and that instability likely means higher prices in the future.”
Paul Pastelok, AccuWeather Lead Long-Range Expert, added: “The impacts of more intense flooding events can be more negative than positive in agriculture, leading to disruptions in crop planting and crop conditions. There can be more frequent and extended delays in planting, more insects which leads to costly insecticides and overall lower yields.”
Pastelok noted that long-range effects ripple into broader patterns. “An increase in flood events in the future can lead to lower surface temperatures in the region impacted, but perhaps a more humid environment during the warm season,” he said.
Why it matters
“These are not just weather statistics,” Root emphasized. “Flood risk is far more sensitive to intensity and event clustering than annual totals; planning for totals alone underestimates today’s hazards.”
Increasing rainfall intensity is already a contributing factor in U.S. weather disasters, with damages routinely measured in billions of dollars. “Greater intensity can raise costs — from infrastructure upgrades and insurance claims to some agricultural production risks — adding economic pressure across sectors,” Root said.
Anderson pointed to the broader trend: “The data already shows more extreme events are occurring, and with more people moving into vulnerable areas, I expect to see more problems in the future.”
How to prepare
For individuals, the advice remains simple: “Preparedness starts with knowing your local flood risk and heeding flash flood warnings,” Root said.
For communities and leaders, the message is broader: “The shift from volume to volatility is the real takeaway. Communities that plan for volatility are the ones that will be most resilient,” Root said. “Resilience means designing infrastructure and drainage systems that can handle today’s higher-intensity events and the likelihood of even higher short-duration rainfall rates in the future.”
Anderson echoed the urgency: “Know your flood risk — even half a mile can make the difference. Pay attention to flash flood warnings. That information can save your life.”
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