The Stormwater Heatmap project springs forth from The Nature Conservancy’s (TNC) Cities program, which strives to bring TNC’s core mission − preserving and protecting the land and waters upon which all life depends − to urban areas. As the leading contributor of toxic pollutants to Puget Sound’s streams, rivers, and marine waters, urban stormwater runoff is a key ecological problem generated by Washington’s urban landscapes. Urban stormwater runoff has harmed virtually all urban and urbanizing streams and rivers, and delivered massive quantities of toxic contaminants to Puget Sound. As a result, the abundance and survival of aquatic species has declined. A recurrent question asked of stormwater managers, eco-toxicologists and ecologists alike, is how much stormwater intervention is needed, and where would you place it for efficient and effective treatment?

This “how much and where” question serves as the foundation of the stormwater heatmap project. The project quantitatively visualizes a pollution loading threat-map for the Puget Sound watershed. The stormwater heatmap uses land use, landcover, stormwater monitoring data, precipitation data, and hydrological modeling to predictively map stormwater pollution loading across the Puget Sound landscape, and quantifies the pollution load on a 1-m2 spatial resolution. This scale allows managers and planners to aggregate data at multiple spatial scales, and allows us to “see” hotspots of pollution loading for a variety of monitored stormwater contaminants. With the pollution visualization layer in place, we can now begin to overlay social-ecological questions in order to develop a stormwater intervention action-map.