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Extreme Flash Flooding Increasing In Frequency Over Last Few Years In Philadelphia Area

PHILADELPHIA (CBS) -- Extreme flooding has become more frequent in the last few years. Flash flooding is a sudden deluge after a heavy rainfall.

Flooding occurs when the ground is unable to absorb all of the water. Urban areas are particularly vulnerable because we have tons of non-absorbant pavement.

And in recent years, we're also getting tons of rain in a short period of time, more often.

"Since early June of this year, we've had 25 flash flood warnings so far, as of mid-july," National Weather Service meteorologist Sarah Johnson said.

If you feel like severe weather and flooding has been occurring more often in the last several years, you're right.

"The last couple of years have been quite active as far as flash flooding," Johnson said.

2018 was a record year for the number of flash flood warnings issued by the National Weather Service Forecast Office in Mount Holly. 2019 and 2020 were above-average years as well.

A flash flood warning means "we're seeing heavy rain on radar or we're getting reports of flash flooding," Johnson said.

And this poses the biggest threat to drivers.

"A lot of the impacts of flash flooding happen to people who are in vehicles. In fact, a majority of flash flood fatalities happen with people that are in vehicles," Johnson said.

A flooded roadway is hazardous for two main reasons which pertain to unknowns.

"You don't necessarily know how deep the water is, and in fact, it takes a lot less water to wash away a vehicle than many people realize. It can take less than 2 feet of water to wash away most vehicles," Johnson said.

Another safety concern is "that you don't know the status of the road below the floodwaters and we've had cases where flash floodwaters washed out the road," according to Johnson.

Johnson says there is only one right thing for drivers to do if they come upon a flooded roadway.

"That they turn around and find another way to get to their destination," Johnson said.

The uptick in flash flooding is due to the prevailing weather patterns over the last several years. But climate change may also playing a role.

If a flash flood watch is in effect and you see the rain pouring down, please stay off the roads if you are able.

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