Multiscale analysis of impervious surface change and environmental equity

Landscape pattern-focused environmental justice (EJ) research has tended to use high-resolution data. Because of the technical difficulties involved in producing high-resolution land cover data for larger extents or at frequent intervals, this research tends to focus on a snapshot in time and a single city or set of cities. This study compares the relationships between impervious cover (IC) and a socioeconomic EJ indicator, EJScreen’s demographic index (DI), using high-resolution EnviroAtlas Meter Urban Land Cover (MULC) data for 24 communities and 30-meter National Land Cover Database (NLCD) percent impervious cover for the conterminous United States. It also uses the NLCD to examine how change in impervious cover over time relates to DI. A contingent probability model was used to measure DI response to NLCD 2019 percent IC, NLCD percent IC change, MULC IC, and surface temperature using Census block groups. We found that although the distribution of change across DI values was relatively uniform, vulnerable block groups (those with high DI values) were more likely to experience large changes in impervious cover and experience hotter urban environments. This research demonstrates that when aggregated by block group, estimates of impervious cover from the NLCD are comparable to estimates from higher-resolution land cover data, and relationships between the DI and impervious cover were similar using both land cover sources. Because the NLCD is available nationwide and updated regularly, this presents opportunities to expand pattern-focused EJ research to a national scale and introduce a temporal component.

Impact/Purpose

This study addresses the question of how the percentage of impervious surface has changed over time and whether these changes are concentrated in Census block groups that are classified as vulnerable based on the demographic index (DI), a socioeconomic environmental justice indicator. High levels of impervious surface can create a health risk by creating heat islands where temperatures are increased. Impervious cover change was measured using the 30-meter resolution National Land Cover Database (NLCD) Percent Developed Impervious for 2001-2019. The distribution of impervious cover change was relatively uniform across DI values, but large increases in percent impervious cover were more likely in vulnerable block groups (those with higher DI). Block groups were also more likely to be classified as vulnerable as the percentage of impervious cover increased, and as the average summer surface temperature increased. Percent impervious cover based on the EnviroAtlas' high-resolution Meter Resolution Land Cover (MULC) was also used for comparison. When summarized by block group, impervious cover from the moderate resolution NLCD was similar to higher-resolution land cover data, and both showed similar relationships between DI and IC and DI and temperature. These findings are significant because they show that large increases in impervious cover have occurred in vulnerable communities that might have fewer resources to mitigate the associated health risks. This research also demonstrates that impervious cover data from the NLCD can be used to add a temporal component to environmental justice analyses. These results could be relevant to policy makers in the urban planning or public health arena, residents of the EnviroAtlas communities included in the study, or researchers interested in using the NLCD to study environmental justice.

Citation

Culler, M. AND Jim Wickham. Multiscale analysis of impervious surface change and environmental equity. IALE – North America Annual Meeting, Riverside, CA, March 19 - 23, 2023.