Urban runoff can deliver a broad spectrum of land-based pollution that degrades nearshore water quality, with cascading effects on coral ecosystem health. Poor water quality can also undermine the natural defense abilities of corals and increase the likelihood of mortality from heat stress.
Pollutants can include household chemicals, oils, trash, sediments, and other toxicants. We derived proxy layers for the impact on nearshore marine ecosystems based on the total area of developed impervious surface (e.g. paved roads, parking lots, sidewalks, and roofs) in 2010, per watershed. We used USGS HU-12 watershed data to aggregate the impervious surface area by drainage to coastal source pixels and used a Gaussian decay function to estimate dispersal offshore, approaching zero at 2 km from shore. Map units are presented as a normalized score from 0 - 1.