Climate Change Will Make Sewer Overflows Up to 7x Worse, No One Is Adapting

Sewer systems across the US were designed based on historical rainfall patterns that no longer reflect reality. Climate change is producing more intense, more frequent storm events that overwhelm systems engineered for a different era. Research published in the Journal of Hydrology projects that the volume of combined sewer overflow inundation will increase by 171% to 716% in future climate scenarios compared to historical baselines. Extreme rainfall events in the US could become three times more likely and up to 20% more severe within the next 45 years. Every percentage increase in rainfall intensity translates directly into more raw sewage entering waterways and backing up into homes. A warmer atmosphere holds more moisture, roughly 7% more per degree Celsius of warming, which supercharges storms to drop more water in shorter bursts. These intense, short-duration downpours are precisely the events that overwhelm combined sewer systems, because the systems have fixed pipe capacity designed for storms that used to be rare but are now common. Cities are caught in a vicious cycle. They are spending billions to remediate CSO problems based on current rainfall data, but by the time these decades-long projects are completed, the rainfall patterns will have shifted again, potentially rendering the new infrastructure inadequate. Philadelphia's $2.4 billion green infrastructure program and similar efforts in Washington DC and Portland are forward-looking, but most cities' long-term control plans do not incorporate climate projections at all. The structural reason this persists is that EPA's CSO policy and consent decrees do not require cities to design for future climate scenarios. Cities are permitted to use historical rainfall data for system design, even though that data is increasingly obsolete. Updating design standards to account for climate change would increase project costs significantly, and neither cities nor the federal government have budgeted for this. The result is that we are spending hundreds of billions to build infrastructure that will be insufficient before it is paid off.