Extreme100-yearfloods could happen every few decades in CT, report shows
Jul. 10—Severe flooding seen Sunday into Monday in the western part of the state could be a prime example of the new normal in rainfall, experts predict. Short, intense storm events followed by flash floods are predicted to become more common.
"The top 10 extreme one-day precipitation events have all occurred since 1995," said Matthew Eby, CEO of First Street Foundation during a presentation earlier this summer. "It is warmer, and the atmosphere holds more water vapor so precipitation events are changing."
The First Street Foundation, a nonprofit research group, released their peer-reviewed precipitation model earlier last year. The model aims to describe future flood risk from climate-driven rainfall events.
Many experts say that NOAA's gold-standard model for predicting precipitation, the Atlas 14, is out of date. In a report published in the magazine Scientific American, NOAA did not dispute the First Street Foundation's claim that their current rainfall model was inaccurate under climate change conditions. The national agency is updating their rainfall prediction models to reflect climate change, but those won't be ready until 2027.
NOAA's current model is primarily out-of-date as it weighs the period of "normal" weather more strongly than our recent bouts of extreme weather, skewing predictions to a pre-climate change state.
"They are correcting back to, essentially, a climate that occurred and that existed in past," said Jeremy Porter, head of First Street's climate implications. "These older records become more problematic in the sense that they don't allow you to understand what is occurring today."
Infrastructure impact
Rainfall prediction models might sound boring, but they're fundamental for planning infrastructure, new construction, industry and agriculture. Without accurate rainfall models new roads, new bridges and houses could be built as if floodwater isn't expected. The "useful life" of bridges and roads could also be dramatically overestimated under current models.
"All of these major infrastructure projects are leveraging Atlas 14 to understand the severity of precipitation events, like how big or thick should the pipe be," said Eby. "The back-of-the-envelope estimates ... that's generated from the amount of precipitation you're seeing."
Across Connecticut, First Street Foundation expects that 15% of all properties have a 1/4 chance of being hit by severe flooding in the next 30 years. This risk isn't distributed evenly across the state. In Bridgeport, only about a fifth of residential homes are at an elevated flood risk, while more than half of critical infrastructure sits in the possible flood zone.
In East Hartford, however, over 41% of all properties in town are at risk of severe flooding over the next 30 years due to its position at a bend of the Connecticut River.
The Foundation predicts that these floods will occur more frequently and with greater intensity than before.
"In the future climate, places like New York pop up where that one-in-100 (flood) occurs about once every 20 years," said Porter. "That's four times as likely" as previously experienced.
The future is already here
Emmanouil Anagnostou, the applied research director for the Connecticut Institute for Resilience and Climate Adaptation, which works directly with the state Department of Energy and Environmental Protection and the University of Connecticut, told CT Insider that he broadly agreed with the prediction that many parts of Connecticut would experience more frequent, intense storms. His research examining rain data nationwide for the past decade shows a clear pattern of climate change-induced transformation in amounts of rainfall here.
"A 50-year event that happened in the decade between 1979-1988 in the current times I would say is five times more frequent," said Anagnostu. "So that means that climate change is already happening. It is not something we just see in the future. It's already intensified."
Anagnostou echoed the recommendation of the First Street Foundation, that our infrastructure built today needs to be built for more intense, and frequent storms. Connecticut, he said, might not be seeing the most extreme climate changes, but that doesn't mean we were getting off free.
"Climate change is directly affecting the intensity of precipitation and how frequently it comes," said Anagnostou. "It puts a lot of our aging infrastructure at risk."
