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Ask a Meteorologist: Why Is It Flooding Where It Seemingly Hasn't Ever Flooded Before?

March 10, 2023 02:15 PM
By: Ready PA

A truck and a car are submerged by flood water

​It’s March, and the theme is flood awareness. As a matter of fact, March 20-24, 2023, is designated by the National Weather Service as Flood Awareness Week in Pennsylvania.

Let's do a thought exercise. Close your eyes and think of flooding. 

What comes to mind? Are you thinking of a raging river or stream? Is the water muddy? 

Ask a friend to do the same, and compare your flooding thoughts. 

Most would likely envision a waterway overflowing its banks, with brown water gushing as tree limbs and other debris float by. This is a pretty common example of what a flood looks like, but would it be odd to imagine a flood in a neighborhood miles away from a major stream or river? How about along a hillside? No, these aren’t stories from a Dr. Seuss tale; these examples have happened right here in the commonwealth in recent years.

What is Pennsylvania’s top hazard?

Pennsylvania’s top hazard is flooding. While your risk of flooding is highest if you live in or near a floodplain, flooding along waterways is not the only game in (your) town. Anywhere it can rain, well, it can flood. In recent decades, Pennsylvania has seen an increase in the number of days with heavy rain events. Heavy rain can cause a few problems

Why is heavy rain such a problem even if you don’t live near a waterway?

First, the sheer amount of rain falling in a short period overwhelms the ground's ability to absorb it. The heavy rain then quickly runs off and collects at a low point or overwhelms a drainage system not designed for so much water at once. If we have wet ground already, the capacity to absorb rain is already diminished. And even if we have really dry ground, the ground acts like pavement and sheds heavy rain quickly

Second, with greater land development, reduction of green space, and the addition of surfaces that cannot absorb water, such as pavement, the water has fewer places to absorb into the ground. These “impervious” surfaces act like a water slide, allowing the water to run off even faster. This can allow water to race down hillsides causing damage, and also allow water to pile up in a low-lying area more quickly, leading to flooding in places never seen previously.

In addition to these two major factors, faster shedding of heavy rainwater can lead to more debris blocking storm drains. An aging stormwater infrastructure in many places across the state cannot handle this added water flow, leading to more flooding. When we see this type of “flash flooding,” the waters often rise very quickly but to higher levels than ever before. Even if the flood waters recede quickly, the damage is done. Flash floods leave us with little time to prepare and low predictability of impact for highly localized flood events away from a waterway.

What can we do to prepare?

Ask yourself these questions: 

  • Am I ready for a flood?
  • What can I do now to keep safe?
Visit the National Weather Service's website for more helpful flooding information.

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