Executive Summary
Stormwater Flooding in New York City
New York City is experiencing increasingly frequent and severe stormwater flooding driven by climate change, aging sewer infrastructure, and extensive impervious surface coverage. Short, intense rain events routinely overwhelm the combined sewer system, triggering Combined Sewer Overflows (CSOs), street flooding, and sewer backups into homes—sometimes during storms producing as little as 0.3 inches of rainfall per hour. These impacts fall disproportionately on low-lying neighborhoods, communities built on historic wetlands, and residents of basement apartments, as tragically demonstrated during Hurricane Ida in 2021.
Limits of Existing Infrastructure Approaches
The City has invested heavily in large-scale gray infrastructure, including the $1.3 billion Gowanus Canal retention tanks. While necessary, these systems address stormwater only after it enters the sewer network and do not reduce runoff at its source. Approximately one-third of New York City’s impervious surface area—primarily rooftops—is located on private property, placing a critical component of stormwater management outside the City’s direct control.
Field Form’s Integrated Approach
Field Form advances a source-control strategy that treats private property as essential stormwater infrastructure. This approach combines lot-level flood exposure mapping, an infiltration suitability analysis that accounts for soil, groundwater, bedrock, and building conditions, and repeatable rooftop runoff diversion systems. These systems can intercept the majority of roof runoff in typical storm events at a fraction of the cost of large-scale gray infrastructure.
Implementation as the Missing Link
Field Form’s experience demonstrates that technical solutions alone are insufficient. Adoption is constrained by limited organizational capacity, complex policy environments, funding gaps, and misaligned insurance structures. To address these barriers, Field Form provides implementation support through their mapping and strategy resource—Flood Form—focused on community capacity building, policy navigation, funding access, and insurance alignment—enabling coordinated, neighborhood-scale action.
Policy Implications and Community Resiliency Districts
This paper calls for expanding public support for stormwater interventions on private property through the creation of community-based Resiliency Districts. Using the Flood Form tool as a shared analytical foundation, these districts would organize residents, property owners, and local institutions within defined sewersheds or NTAs around coordinated flood mitigation strategies. By grounding organizing efforts in lot-level exposure data and aggregated neighborhood risk profiles, Resiliency Districts can identify priority blocks, set measurable runoff reduction targets, and pursue bundled technical and financial solutions.
Critical Implementation Pathways
To translate the strategies outlined in this paper into measurable reductions in stormwater runoff and flood risk, a coordinated set of near-term actions is required. The following steps are intended to advance the integration of private property interventions, community-based organization, and public sector support into an operational framework capable of scaling across New York City.
Pilot Priority Stormwater Resilient Districts
Initiate 2–3 pilot Stormwater Resilient Districts (SRDs) in high-risk Combined Sewer Outfall areas, including Owls Head–007 in Park Slope/Gowanus. These pilots should leverage the Flood Form tool to identify priority blocks, recruit participating property owners, and define neighborhood-scale runoff reduction targets. Building on the Flood Club model, these districts would formalize local organizing structures, coordinate installations across multiple properties, and establish baseline performance metrics to evaluate impact over time.
Establish a Stormwater Diversion Subsidy Program
The New York City Department of Environmental Protection (DEP), in coordination with the Mayor’s Office, should design and administer a dedicated subsidy program to support installation of private property stormwater diversion systems. Modeled on the existing Green Infrastructure Grant Program, funding should be directly tied to gallons of stormwater retention or diversion capacity installed. DEP would establish technical standards, verification process, and integration with Long Term Control Plans, while MOCEJ would ensure alignment with citywide climate adaptation priorities and equity goals. Initial funding allocations should prioritize SRD pilot areas to maximize near-term impact and demonstrate cost-effectiveness relative to gray infrastructure investments.
Deploy Flood Form Reporting
The NYC Department of Environmental Protection (DEP), in partnership with the Department of City Planning (DCP) and Field Form, should formalize and expand the production of sewershed level flood exposure and infiltration reports using the Flood Form tool. SRDs, supported by community-based organizations— groups such as the Fifth Avenue Committee and local development corporations—would serve as implementation partners, using these reports to support neighborhood organizing, inform local planning processes, and guide participation in subsidy programs.
Create a Dedicated Stormwater Implementation Entity
The Mayor’s Office, in coordination with the New York City Council, should establish a dedicated Stormwater Department or interagency Stormwater Implementation Office to coordinate distributed stormwater management efforts. This entity could be modeled on the Berlin Rainwater Agency and headed by the city’s Chief Climate Officer. Establishing such an entity would consolidate responsibilities currently fragmented across DEP, NYC Emergency Management (NYCEM), and many others, and would be charged with administering subsidy programs, coordinating interagency policy, and providing direct technical assistance to property owners and SRDs. The City Council would authorize its formation, define its mandate, and allocate baseline funding through the capital and expense budget. This body would also be responsible for tracking performance metrics, ensuring compliance with regulatory requirements, and prioritizing investments in high-risk and historically underserved communities.
Collectively, these steps establish a clear pathway from analysis to action—linking data, design, funding, and community organization into a cohesive model for reducing stormwater impacts. By investing in both the physical and social infrastructure required to manage runoff at its source, New York City can accelerate progress toward its CSO reduction goals while building a more resilient and equitable urban environment.