Extreme rainfall in Pa. is increasing, new report finds


The report ‘Extreme precipitation in a warming climate’

A report from Climate Central notes that the cost of flood damage in Pennsylvania was approximately $2.8 billion in 2020 and that figure could increase by 8 percent by 2050 if global temperatures continue to rise. Pictured is the Susquehanna River in 2016. (CBF photo)

HARRISBURG, Pa. — A new report suggests the devastation from extreme rain events that claim lives, cause billions of dollars in damage and pollute local waters will become more severe in Pennsylvania if left unchecked, thanks to climate change.

The report “Extreme precipitation in a warming climate,” by the science communications group Climate Central, predicts that, on average, U.S. counties are likely to experience a 17 percent increase in extreme rainfall on the heaviest 1 percent of days. Much of the data in the report comes from the US Global Change Research Program’s Fifth National Climate Assessment.

According to the report, for every 1°F of warming, the air can hold an additional 4 percent moisture.

The Chesapeake Bay Foundation (CBF) notes that one inch of rain falling on an acre of paved surfaces, such as streets and parking lots, produces 27,000 gallons of runoff. Rainwater flowing over impervious surfaces often picks up oil, grease, dirt and nutrients (nitrogen and phosphorus) and flows into nearby waterways.

According to the state’s latest report on impaired waters, 3,828 miles of Pennsylvania’s rivers and streams are not meeting water quality standards due to contaminated urban stormwater and storm sewers. It is the third most important source of limitations.

The report shows how much more rain is likely to fall in each Pennsylvania county during severe storms if the climate warms by 2°C. That includes Bucks County, 23.9 percent; Philadelphia, 22.5 percent; Center County, 30.0 percent; Allegheny County, 17.4 percent; Lancaster County, 16.9; and Luzerne County, 15.8.

The Climate Central The report notes that as the climate warmed between 1958 and 2021, the strongest storms now drop 60 percent more rain in the Northeast (including Pennsylvania, Maryland, the District of Columbia, New York and West Virginia) and 37 percent more in the Southeast (including Virginia).

This increases the chance of heavier rainstorms that contribute to flash floods like the one that killed seven people in southeastern Pennsylvania last summer.

A grandmother, mother and her two children were swept away by rushing water after nearly 5 inches of rain fell in Bucks County in 45 minutes last July. The mother and two-year-old daughter were killed and the search for the nine-month-old son was halted. The father, a 4-year-old son and the grandmother survived. Four other people died that day from Bucks County flooding.

Climate Central reported that flood damage costs in Pennsylvania were approximately $2.8 billion in 2020 and that figure could increase by 8 percent by 2050 if global temperatures continue to rise.

Harry Campbell, CBF Science Policy and Advocacy Director for Pennsylvania, issued the following statement:

“The consequences of climate change extend far beyond warmer summer temperatures.

“The Susquehanna River is already one of the most flood-prone rivers in the country, and combined with Pennsylvania’s aging infrastructure in many cities, costly flooding is likely to increase in the coming years.

“The intense rainfall is also likely to increase the amount of polluted water flowing into our lakes, rivers and streams.

“When rainfall hits a hot surface, such as a parking lot, the sun’s energy is transferred to the cooler rainfall as it makes its way to the nearest body of water. This superheated rainwater can be so hot that it can cause serious damage to critters that rely on clean, cool water to survive, such as brown trout and the eastern hellbender.

<“Because hotter water holds less dissolved oxygen than cold water, many critters will find it harder to breathe. If it doesn’t kill them, it can make them susceptible to pathogens and diseases. To make matters worse, some pollutants can become more toxic in warmer waters.

“There is one thing almost every homeowner, community and business can do to mitigate these negative impacts. Planting and preserving native trees, shrubs and other vegetation along streams, streets and other sensitive areas helps slow, disperse and absorb precipitation, filter out pollutants and cool runoff.”

–BJ Small, Chesapeake Bay Foundation

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