Pittsburgh region faces increasing rain, flood risks as planet warms

Severe storms intensified by global warming are bringing worse rain and flooding to the Pittsburgh area on a more frequent basis than currently estimated by the federal government, according to a recently released report from the First Street Foundation.

Allegheny County could see nearly 4 inches of rain per hour during 1-in-100-year storms, the report showed, about 40% more than the 2.6 inches per hour currently estimated by the government. Storms that once struck every 100 years, meaning there’s a 1% chance each year of them occurring, could now happen in Allegheny County every 25 years. They could hit the city of Pittsburgh every 20 years.

Additional rain also brings the risk of increased flooding. About 86,000, or 1 in 7, residential properties in Allegheny County are potentially in the floodplain for a 1% storm, according to the report. That’s nearly 50 times the 1,750 properties currently identified by the government, and the largest increase of any county in Pennsylvania.

First Street, which studies risks posed by climate change, analyzed government-collected rainfall data from 2002-21 to calculate its projections. Those peer-reviewed numbers are much newer than the decades-old figures used by the government in its Atlas 14 product, the next version of which won’t be finalized until 2027.

Jeremy Porter, the foundation’s head of climate implications research, told the Union Progress that the government “severely underestimates” rainfall rates, and that creates problems for both residents and local governments.

“Both the need to protect personal property, as well as community residents, is underestimated via the need to buy flood insurance and the need to build adaptation  — levees, flood barriers, etc. — to protect local communities,” he said.

After the Great St. Patrick’s Day flood in 1936 that inundated Downtown Pittsburgh — some buildings still retain high-water marks — the federal government began constructing a series of flood-control projects. The U.S. Army Corps of Engineers now maintains 16 control sites throughout its Pittsburgh district, stretching from northern West Virginia to where the Allegheny River crosses over from New York.

Megan Gottlieb, who oversees the water management unit, said detailed manuals guide the storage and release of water. She said weather patterns have changed and she now sees more storms that dump a lot of rain but only last for a short time.

The Corps doesn’t release information about the condition of its dams, citing national security concerns, and instead issues “risk assessments” on a 1-to-5 scale of “very high” to “very low.” The area’s flood control dams were mostly ranked as “low” or “very low” risk, although the Kinzua was “high” risk, and three placed in the middling “moderate” category — the Youghiogheny, Michael J. Kirwan and Conemaugh.

“These reservoirs, even though they’re old, they are solid,” Gottlieb said. “We’re always looking at our reservoirs and making sure that they’re providing those benefits, even when we get a two-day notice that we might have a lot of rain. It’s so important that these dams function for that public safety component.”

Accurate rainfall and floodplain estimates are crucial for a variety of private development and public works projects.

Properties located within Pittsburgh’s 100-year floodplain face special requirements, such as being at least 1½ feet above the base flood elevation, and homes and businesses with government-backed mortgages are required to purchase flood insurance. The floodplain — meant to be reviewed every five years but largely untouched since 2014 — currently includes sections of Sharpsburg, Millvale and McKees Rocks, among other places.

First Street’s report suggested the floodplain include more of those river towns, as well as parts of Oakmont and Carnegie, and the Strip District, South Side and Lawrenceville neighborhoods in Pittsburgh.

Audrey Wells, a spokesperson for Pittsburgh’s planning department, did not directly respond to questions about floodplain management. She noted that city planners have access to rainfall figures calculated specifically for Pittsburgh by Carnegie Mellon University researchers, which take climate change into account.

A spokesperson for the Federal Emergency Management Agency, which designates floodplains, said it’s currently studying the full length of the Ohio River and plans to release updated flood maps in 2028 at the earliest. The spokesperson added that FEMA “recognizes” that its maps do not “comprehensively capture all flood hazards or all degrees of flood risk.”

“While FEMA sets minimum standards through the National Flood Insurance Program, we encourage communities to utilize the best available data they have to adopt standards that can help their residents,” the spokesperson said. “For example, many communities require buildings to be elevated several feet above the minimum standard established by the [floodplain], or they can implement floodplain management in areas outside of the [floodplain].”

The slopes that dot the city are naturally at risk for sliding, but torrents of rain can exacerbate the problem. Zoning rules already require detailed inspections before development can happen in landslide-prone areas, and some hillsides have been essentially marked as off limits.

Wells said a key part of preventing landslides is better managing stormwater, noting the city and its water authority worked together on a stormwater code revision that took effect last year. The update includes the Pittsburgh rainfall figures calculated by CMU.

“We want to make sure that as a department, we’re working to mitigate the effects of landslides, and to minimize future ones from happening,” she said.

Heavier rainfall is especially unwelcome news for the Allegheny County Sanitary Authority, which handles water treatment for two-thirds of the county’s 130 municipalities. Stormwater is often combined with wastewater on the way to Alcosan’s processing facility, creating a rush of water that frequently becomes too much to handle, causing overflows into the Allegheny, Monongahela and Ohio rivers.

The authority entered into its most recent agreement four years ago with the federal and state governments to drastically reduce its dumping. A plan estimated to cost $2 billion, based on rainfall estimates that used 2003 as a “typical year,” includes expanding treatment capacity and building three underground tunnels to store and move wastewater.

Jordan Fischbach, who has analyzed Pittsburgh-area water management for the Rand Corp. and now works for a Louisiana-based nonprofit, told the Union Progress that the aging local water infrastructure is “not sized and not designed for the conditions that we’re experiencing today, and it is certainly not ready for the conditions that could come in the future.” Even the expensive Alcosan plan could be considered a “down payment.”

“More work is going to be needed, and that scale of investment is going to be much higher than has been previously discussed,” he said.

Alcosan didn’t respond to multiple requests for comment.

Fischbach said a growing problem for governments is not being able to rely on stable historical data in the way they once did for long-term planning. Some researchers now push for infrastructure projects that are oversized or can be adapted in future years to changing needs.

“Developing a static plan that’s supposed to give you infrastructure for 50 years or 100 years isn’t going to work anymore,” he said. “Instead of planning for what you think is most likely today, and then crossing your fingers, you’re instead taking into account the possible futures you might see, understanding and acknowledging that there’s uncertainty there, and then building a plan that is more robust and can be adaptive in light of that uncertainty so you’re not caught by surprise.”