Indicator ES.2.d Impervious ground surfaces
Descriptive Title: Proportion of ground covered with impervious surfaces
Geographic Unit of Analysis: County
| Percentage of ground cover distribution by land-use in San Francisco | ||||||
|---|---|---|---|---|---|---|
| Land use | Bare Soil | Duff/Mulch | Herbs | Water | Impervious* | Building |
| Commercial/Industrial | 1.2 | 3.9 | 3 | 5 | 54.8 | 32.2 |
| Institutional | 6.6 | 1.7 | 28.2 | 0 | 41.6 | 22 |
| Street/ROW** | 2.9 | 0.1 | 13.4 | 6.7 | 66.5 | 10.3 |
| Open space | 8.5 | 6.9 | 43.6 | 13.7 | 26.3 | 1 |
| Residential | 4.8 | 0.9 | 14.4 | 0.1 | 30.5 | 49.2 |
| Vacant | 6.3 | 0 | 31.7 | 5.2 | 28.9 | 27.9 |
| *impervious surfaces include: streets, driveways, sidewalks, parking lots | ||||||
| *pervious surfaces include: bare soil, duff/mulch, herbs and water | ||||||
| **ROW = right of way. | ||||||
Why Is This An Indicator Of Health and Sustainability?
Pervious surfaces allow natural ground absorption of rainfall, replenishing groundwater tables and reducing the amount of storm-water runoff to the Bay. In turn, contaminant runoff to the Bay is reduced and residents swimming or fishing in the Bay have reduced exposure to oils, lead, and other toxins. In addition, pervious surfaces reduce sewage system loads by assimilating large amounts of rainwater. This reduces the potential for untreated sewage to be discharged, creating unsanitary conditions in the ocean and on the beach.Interpretation and Geographic Equity Analysis
Dominant ground cover types in San Francisco include herbaceous (i.e., grass, gardens) (34%), impervious surfaces excluding buildings (i.e., driveways, streets, sidewalks, parking lots) (43%), and buildings (26%).
According to the Environmental Protection Agency, "impervious or impermeable surfaces" are defined as surfaces that either do not allow, or allow only with great difficulty, the movement or passage of water.
Methods
In order to identify and quantify the percentages of pervious and impervious surfaces in San Francisco, , the USDA Forest Service Urban Forest Effects (UFORE) model was utilized. The UFORE model uses standardized data from randomly located plots, and local hourly air pollution and meteorological data to quantify urban forest structure and numerous urban forest effects. In addition to measuring urban forest structure, the model also estimates ground cover and land-use. To determine ground cover distribution, a total of 200 one-tenth acre field plots throughout the city were randomly located based on land-use and analyzed using the UFORE model.
Limitations
Although porous pavement is generally recommended in most areas for its benefits related to storm water runoff and decreased heat retention, porous pavement should be considered carefully in areas heavily traveled by idling cars and trucks. For more information on porous pavement, see June 2005 EPA-commissioned report on Cool Pavement. Available at: http://www.epa.gov/heatisland/resources/pdf/CoolPavementReport_Former%20Guide_complete.pdf
Data Source
Ground cover figures and chart from San Francisco Department of the Environment, USDA Assessing Urban Forests Effects (UFORE) and Values: San Francisco's Urban Forest, Accessed on July 19, 2006: http://www.sfenvironment.org/downloads/library/sfuforefinal.pdf
Environmental Protection Agency, Terms of Environment. Accessed on July 19, 2006: http://www.epa.gov/OCEPAterms/