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. And from 1958 to 2016, the heaviest 1% of rainfall events became 55% and 42% wetter in the Northeast and Midwest, respectively—and 9-29% wetter for all other regions. 

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.

In the U.S., the Northeast and Midwest are expected to see ~40% increases in the extreme 1% of rainfall events by the end of the century with additional 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.