Reducing Runoff: The Role of Urban Natural Areas in Stormwater Management

Urban stormwater management is a growing challenge in the face of climate change, especially in cities like New York with aging gray infrastructure and increasing impervious surfaces. This report, “Reducing Runoff: The Role of Urban Natural Areas in Stormwater Management,” presents a comprehensive analysis of how urban natural areas, including forests, wetlands, and meadows, play a critical yet often overlooked role in mitigating stormwater impacts.

Using the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model and high-resolution spatial data, this report quantifies stormwater retention across land cover types in New York City, Baltimore, and New Haven while highlighting the need for high-quality data on the presence and condition of urban natural areas. Natural areas in NYC alone absorb an estimated 17% of all urban stormwater, a contribution valued at up to $760 million annually in avoided treatment costs.

The findings show that natural areas consistently outperform other green infrastructure in stormwater capture when normalized by land area, and that forest health significantly enhances this capacity, as healthy forests can absorb up to 10% more stormwater than degraded ones.

Yet, natural areas remain underrepresented in urban stormwater planning, in part due to the lack of high quality spatial data. This report demonstrates how mapping natural areas, even using parkland as a proxy, can greatly improve our understanding of their ecological and economic value.

This work supports the mission of the Natural Areas Conservancy by highlighting the essential role that urban natural areas play in building climate-resilient cities. By preserving, restoring, and integrating these ecosystems into stormwater infrastructure planning, we can protect both human communities and natural habitats while advancing equitable, cost-effective environmental solutions.

In a nutshell, this resource offers:

• A discussion of how stormwater is handled in cities, and how green infrastructure can improve stormwater capture. 
• Case studies of natural area stormwater capture from three cities.
• A call to action for city residents, planners and agencies. 

How to use this resource:

• As an example when advocating for natural areas. 
• As a guide for researching stormwater capture in natural areas.

Author: Jeffrey A. Clark

Date published: July 28, 2025

Point of contact: Dr. Jeffrey Clark at jeffrey.clark@naturalareasnyc.org

Citation: Clark, Jeffrey A. G., Clara Pregitzer, and Crystal A. Crown. Reducing Runoff: The Role of Urban Natural Areas in Stormwater Management. New York: The Natural Areas Conservancy, 2025.

Resource is available online here.