Urbanization and the Loss of Resource Lands in the Chesapeake Bay Watershed

Abstract

We made use of land cover maps, and land use change associated with urbanization, to provide estimates of the loss of natural resource lands (forest, agriculture, and wetland areas) across the 168,000 km2 Chesapeake Bay watershed. We conducted extensive accuracy assessments of the satellite-derived maps, most of which were produced by us using widely available multitemporal Landsat imagery. The change in urbanization was derived from impervious surface area maps (the built environment) for 1990 and 2000, from which we estimated the loss of resource lands that occurred during this decade. Within the watershed, we observed a 61% increase in developed land (from 5,177 to 8,363 km2). Most of this new development (64%) occurred on agricultural and grasslands, whereas 33% occurred on forested land. Some smaller municipalities lost as much as 17% of their forest lands and 36% of their agricultural lands to development, although in the outlying counties losses ranged from 0% to 1.4% for forests and 0% to 2.6% for agriculture. Fast-growing urban areas surrounded by forested land experienced the most loss of forest to impervious surfaces. These estimates could be used for the monitoring of the impacts of development across the Chesapeake Bay watershed, and the approach has utility for other regions nationwide. In turn, the results and the approach can help jurisdictions set goals for resource land protection and acquisition that are consistent with regional restoration goals.

Fuzzy image regions for estimation of impervious surface areas

“…ISA change was calculated as the difference between ISA values in the two dates. Figure 4(b) shows the urban development reference data (Jantz et al 2005). Figure 4 shows that, using the proposed method, a general overestimation occurs over the whole study area.…”

“…ISA maps represent impervious surfaces as a continuous variable, with values ranging from 0% (no impervious) to 100% (completely impervious). In addition, qualitative land cover maps for the same dates are available from the mid-Atlantic Regional Earth Science Applications Center (MA-RESAC) (Jantz et al 2005). These thematic maps represent five land cover categories: water, urban, grass, trees, and bare soil.…”

“…As part of an extensive study on urbanization in the Chesapeake Bay Watershed, Jantz et al (2005) obtained accurate ISA maps for 1990 and 2000. In the study area, ground reference data were collected by rasterization of visually interpreted aerial photographs at 3 m spatial resolution.…”

“…As a final result, percentages of impervious surface and canopy cover were obtained. Jantz et al (2005) used a similar approach for mapping impervious surface areas (ISAs). A decision tree algorithm, trained with samples collected visually from high spatial resolution orthophotos, was used to obtain impervious surface percentage values from principal components and vegetation indices derived from Landsat TM and ETMþ bands.…”

Satellite maps show Chesapeake Bay urban development

“…Two maps of the built environment, expressed in terms of impervious surface area, have been derived for areas that encom pass the 168,000-square-kilometer Chesapeake Bay watershed (Figure l),a region that has been highly altered by human land use [Goetz et al, 2004;Jantz et al, 2005]. One map was developed for the region at fine (30-square-meter) spatial resolution, and the other covers the extent of the conterminous United States at one-square-kilometer resolu tion [Elvidge et al, 2004].A finer-resolution regional map was used to assess the quality of the national map, demonstrating the utility the latter map for a range of applications related to monitoring land transformation and assessing watershed impacts.…”