Increasing Rainfall Worsens Combined Sewer Overflows

Posted on June 1, 2025

By Julianna D’Addona
UConn Journalism

As pre­cip­i­ta­tion increas­es and storms become more severe across the Northeast, com­bined sewage sys­tems are being inun­dat­ed with mix­tures of sewage and rain­wa­ter. The net­work erupts, send­ing untreat­ed waste into Hartford’s Park River and back­ing into some people’s hous­es.

Because of a warmer, more humid cli­mate, rain­fall in the Northeast has been increas­ing over the past sev­er­al decades. A 2023 study by researchers and stu­dents at Dartmouth College projects that extreme storms—at least 1.5 inch­es of rain or snow in one day—will increase by 52% by 2100. The study cre­at­ed a model for 2070 to 2099 using his­tor­i­cal pre­cip­i­ta­tion data from  the National Center for Atmosphere Research.

Hartford is already see­ing the effects of more rain, said Dr. Mark Mitchell, for­mer Hartford direc­tor of health and found­ing mem­ber of the Connecticut Coalition for Environmental Justice.

“With cli­mate change, we’ve got­ten a lot more down­pours. That’s one of the things you see with cli­mate change,” Mitchell said.

Warmer air fuels more intense storms, and the tem­per­a­ture in Connecticut has increased by about 3 degrees F, accord­ing to data pro­vid­ed to the state from the University of Connecticut Institute for Resilience and Climate Adaptation (CIRCA).

CIRCA’s cli­mate assess­ment reports are designed to help cities and towns pre­dict and deal with increased flood­ing.

Mary Looney, who worked as a munic­i­pal stormwa­ter edu­ca­tor for the University of Connecticut’s Center for Land Use Education and Research, said, “What we’re see­ing is real­ly intense peri­ods of drought, of dry weather—and then, we’re get­ting real­ly real­ly intense rain­fall; we’re see­ing sev­er­al inch­es in an hour.” Looney cur­rent­ly works for the Bristol-Burlington Health District.

“Such intense rain­storms are going into one pipe that often­times can­not han­dle the flow and veloc­i­ty of the water that is going into it,” Looney said.  

“This is over­whelm­ing our sys­tems,” Looney said. “It’s lead­ing to more com­bined sewer over­flows, more bac­te­ria exceedances. It’s con­se­quen­tial for our shell fish­ing indus­tries, for any­one who’s eat­ing raw shell­fish and items like that. So, it def­i­nite­ly harms the pub­lic in a way that is not often thought of right off the bat.”

TOP IMAGE: Over time, rain­fall is increas­ing in Connecticut. Although 2025 has been a rel­a­tive­ly dry year, 2023–24 was very wet. The added rain makes com­bined sewage over­flows worse. Map from the Northeast Regional Climate Center.