Climate Matters
Rising Hourly Rainfall Intensity
Hourly rainfall intensity—a key factor in flash floods—has increased since 1970 in 136 U.S. locations analyzed by Climate Central.
Extreme Weather Toolkit: Heavy Rain and Flooding
Climate change is bringing heavier rainfall extremes and increased, inequitable flood risk to many parts of the U.S.
For every 1°F of warming the air can hold an extra 4% of moisture, increasing the chances of heavier downpours that contribute to the risk of flash floods.
The rapid onset of flash floods limits time to get people out of harm’s way. In the U.S., racial minorities and those living in mobile homes are disproportionately exposed to flood risk, especially in the South and in rural areas.
In the U.S., extreme daily rainfall has become more frequent since the 1980s. Hourly rainfall intensity has also increased since 1970 — by 13% on average across 150 U.S. locations analyzed by Climate Central.
And from 1958 to 2021, the heaviest 1% of rainfall events became 60% and 45% wetter in the Northeast and Midwest, respectively — and 1% to 37% wetter for all other regions in the continental U.S.
Changes in rainfall from 1988 to 2017 accounted for one-third of U.S. flood damages (about $73 billion) over that same period. And the most intense downpours caused the largest damages.
The latest IPCC reports indicate that precipitation extremes are likely to increase globally, even in regions with decreasing average precipitation.
Most of the U.S. is projected to see increases in precipitation extremes with 2°C (3.6°F) of warming.
With high future levels of heat-trapping emissions, U.S. flash floods could also intensify — especially in the Southwest. A recent study suggests that the burdens of an estimated 26% increase in overall U.S. flood risk by 2050 could disproportionately impact Black communities along the Atlantic and Gulf coasts.
Updated: April 2024
Resources
These resources explore the science, trends, and local impacts of heavy rain and flooding in the U.S.
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