What to Do When There’s a Flash Flood Warning

When heavy rainfall occurs in a short period of time, rushing water can deluge homes and basement apartments, overtake cars and knock people off their feet. Flash floods can develop quickly, within hours or even minutes; and they often catch people off guard, killing an average of 88 people in the United States each year.

“Flash floods occur when there’s just too much water coming in too fast,” said Bonnie Schneider, a meteorologist and author of “Extreme Weather.” And climate change is compounding the risks: Warmer air holds more moisture, Ms. Schneider said, which can lead to heavier, more intense rainfall.

Though flash floods are scary, experts say you can increase your odds of survival by staying informed and having a plan. Here’s what to do in advance — and in the moment — to get through a flash flood safely.

Understand the difference between the various alerts.

The National Weather Service currently issues severe weather alerts in English and Spanish.

If there’s a “flash flood watch,” according to the service, flooding is not guaranteed, but conditions are favorable enough for it to be possible, so be prepared to change your plans.

A “flash flood warning” means a flash flood is imminent or already occurring, and you should immediately move to higher ground if you’re outside or in a basement apartment.

The most dire alert is a “flash flood emergency,” which indicates that not only is flooding occurring, but it’s posing a severe threat to human life. In 2021, New York City received its first notification of this type during heavy rainfall caused by Hurricane Ida.