Impervious Surfaces are hard surfaces (e.g., paved roads) that prevent water from soaking into the ground. These surfaces increase the amount of water running off the landscape while picking up pollutants along the way. These surfaces also affect local temperatures and increase heat in urban areas. This indicator assesses the amount of impervious surfaces in a watershed using thresholds from the NOAA Office for Coastal Management (NOAA Guidelines).
How is it scored?
The percentage of impervious surfaces in a watershed was calculated at the census block level. The amount of impervious surfaces in a census block was converted to a 0–100 scale using two equations (Table 1). The census block score was area-weighted to calculate a watershed score. Watershed scores were area-weighted to calculate an overall regional score.
Table 1. Scoring thresholds and equations for the percentage of impervious surfaces.
Impervious Surface % | Score | Equation |
20–5 | 0–59 | y = -8x + 100 |
5–0 | 60–100 | y = -4x + 80 |
Data source: NLCD 2019 (https://www.mrlc.gov/data?f%5B0%5D=category%3AUrban%20Imperviousness).