WASHINGTON — Pedestrians trudging along city streets knee-deep in water. Cars floating down roads like ships on a river. Basements overflowing with water.

Here is a closer look at deadly flash floods and why they have become increasingly common in the United States.

What is flash flooding? 

Flash or sudden flooding usually occurs after heavy rainfall, when the ground cannot absorb all the water. According to the US National Weather Service, flash floods usually take place within three to six hours after a storm.

Dam and levee breaks as well as mudslides can also lead to rapid flooding.

“Flash flooding occurs so quickly that people are caught off-guard,” the NWS says on its web site.

Cities and towns are especially prone to flash floods because urban surfaces don’t allow water to be absorbed by the ground and it quickly streams to low spots.

Extreme weather leads to more floods 

Floods are the most common and among the most deadly natural disasters in the US, according to the Natural Resources Defense Council, an environmental advocacy group.

So far this year, 80 people have been killed in floods, according to government data.

Scientists say that climate change is playing a role in the increased frequency of flash floods with rising global temperatures causing longer heat waves, droughts and heavier rainfall around the world.

The Natural Resources Defense Council predicts that America’s flood hazard areas are expected to grow 45 percent by the end of the century.

Flood warnings 

Flash floods can trap people inside buildings or cars. If flooding occurs, people should immediately get to higher ground, according to the NWS.

Driving through flooded roadways or walking through moving water is dangerous, as road beds may be washed out under flood waters.

“Six inches of moving water can make you fall. If you have to walk in water, walk where the water is not moving. Use a stick to check the firmness of the ground in front of you,” the weather service advises on its web site. “Turn around, don’t drown!”

Another danger posed by floods is snakes, insects and other animals that can end up in the water, according to the Red Cross. Americans are encouraged to monitor weather conditions and follow flood warnings they receive on their cell phones from local authorities.