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EPA Calls on NYC to Use Rainfall Data Based on Climate Projections for Our Region

Recently, as part of its response to a City Planning Department Environmental Impact Statement (EIS) for the Gowanus Neighborhood Rezoning Plan, the EPA called out the modeling data that NYC Department of Environmental Protection provided for estimated stormwater impacts from proposed new development and sewer build outs. The data do not incorporate the city’s projections for increased precipitation due to climate change.


In a letter to the NYC Department of Planning, EPA Region 2 officials recommended that the city use more up-to-date climate projections for our region rather than the 2008 data they’d used for the EIS. Here is a link to an article about the EPA’s comments which details the EPA’s concerns about the city’s stormwater calculations and modeling data. While the EPA letter is specific to the Gowanus Rezoning EIS, the comment applies across the board to all city planning.

For many years now, SWIM has noted in our public testimonies and comment letters that the rainfall data upon which the City’s CSO Long Term Control Plans (CSO LTCP’s) for our critical wastewater system upgrades do not reflect the rainfall projections for our region in the year 2030 (when most of these plans will be completed).


In 2019, SWIM challenged the City’s use of 2008 rainfall data with water quality testing results collected by several citizen scientist groups who are SWIM member organizations. You can read about that in our blog post here. We called on the city to check the modeling and data it was using to ensure it reflects current and future rainfall scenarios. NYC officials maintained at the time that the rainfall data they were using reflected the current conditions for precipitation in our region.


What we know for sure is that we’ve had CSO alerts for nearly every waterbody in the city on a regular basis due to frequent and heavy rains this year and in recent years. If our critical stormwater and wastewater infrastructure is already being pushed past capacity ~ 15 -20 times per year now (sometimes by as little as one tenth of an inch of rain), how will it handle what we’ll face in the year 2030 and beyond? We got a glimpse of what that might look like this summer with just the remnants of hurricanes Henri and Ida.


The downpours from Henri and Ida created extreme flooding conditions which caused devastating loss of life and overloaded the capacities of our critical infrastructure: roads, rooftops, subways, stormwater and wastewater systems, parks and green spaces and so much more. We need to make significant adaptations now to account for what we know lies just ahead.


The years ahead will require that newly developed private properties install stormwater management systems on site. There are several incentive programs that will help catalyze this effort citywide. All of these incentives, listed in the recently released NYC Stormwater Resiliency Plan, need to ensure that the stormwater management systems are designed and built using the most up to date projections for regional precipitation.

Importantly, the Stormwater Resiliency Plan states that accurate modeling is vital and even notes (see page 5) that current modeling for the city’s sewer system is very likely insufficient. City officials clearly need to pivot now and base all of our critical infrastructure plans on the NYC Panel on Climate Change projections for future conditions.

Resources to delve into this matter further:


The NYC Stormwater Resiliency Plan


An article in The City from September 3, 2021 mentions the Stormwater Resiliency Plan and delves into the vulnerabilities of NYC's drainage systems


An article in the NY Daily News quoting NYC Mayoral candidate Eric Adams saying the City needs to base their plans on future rainfall predictions


An article in Curbed about the impacts of Ida in NYC (this article is the source for the first image in this blog post)


NYC Urban Field Station 2021 White Paper: Living with Water: Documenting Lived Experience and Social- Emotional Impacts of Chronic Flooding for Local Adaptation Planning


Grist article on how cities can prepare for climate change






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