Developed
Developed Gains Developed Loss
What is an impervious surface?
An impervious surface is composed of any man-made material that impedes or prevents the natural infiltration of water into the soil mantle. Such surfaces include building roofs, patios, sidewalks, concrete or asphalt streets, parking lots, and gravel roads. This definition does not include rock outcroppings or compacted earthen materials that could also increase or divert water flow, thus preventing infiltration.
Why is the impervious surface area of the landscape relevant?
When impervious surfaces cover areas where water naturally seeps into underground water sources, or aquifers, they reduce the amount of water available to recharge wells and springs. During storms, excess water that could not seep into the ground flows across impervious surfaces where it can gather harmful pollutants (e.g., oil and fertilizer) and deposit them into surrounding waters and farther downstream. As impervious surfaces increase, so do stormwater runoff volumes, the velocity of stormwater flows, and pollutant levels in runoff (Schueler, 1994).
How is impervious different than development?
Developed features are made up of impervious surfaces, but also include the grasses (and potentially smaller amounts of other cover types, such as individual trees in yards) that surround these man-made impervious features.
What developed classes are mapped in the Land Cover Atlas?
In the Regional land cover data, produced for the Contiguous United States (CONUS), we map 4 categories of developed features. These include:
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Developed, High Intensity - Each pixel comprises 80 to 100 percent concrete, asphalt, or other constructed materials. Vegetation, if present, occupies less than 20 percent of the landscape. This class includes heavily built-up urban centers and large constructed surfaces in suburban and rural areas with a variety of land uses.
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Developed, Medium Intensity - Each pixel comprises a mixture of constructed materials and vegetation or other land cover. Constructed materials account for 50 to 79 percent of total area. This class commonly includes multi- and single-family housing areas, especially in suburban neighborhoods, but may include all types of land use.
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Developed, Low Intensity - Each pixel comprises a mixture of constructed materials and substantial amounts of vegetation or other land cover. Constructed materials account for 21 to 49 percent of total area. This class commonly includes single-family housing areas, especially in rural neighborhoods, but may include all types of land use.
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Developed, Open Space - Each pixel comprises a mixture of some constructed materials, but mostly managed grasses or low-lying vegetation planted in developed areas for recreation, erosion control, or aesthetic purposes. Constructed surfaces account for less than 20 percent of total land cover.
- In the High Resolution land cover, produced for the Pacific and Caribbean Islands, we map two categories of developed features. The various intensities of development are no longer applicable, as areas are mapped with a significantly higher level of spatial detail where features or either impervious or not. These categories include:
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Impervious - Anthropogenic features such as buildings, parking lots and roads developed from asphalt, concrete or other constructed surfaces which do not allow infiltration from precipitation.
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Developed, Open Space - Each pixel comprises a mixture of some constructed materials, but mostly managed grasses or low-lying vegetation planted in developed areas for recreation, erosion control, or aesthetic purposes. Constructed surfaces account for less than 20 percent of total land cover.
How is a pixel's percentage of imperviousness calculated?
In the Regional land cover data (CONUS area) Coefficients were derived for each of the four Coastal Change Analysis Program (C-CAP) developed categories. These values were based on National Land Cover Database (NLCD) 2001 Imperviousness data (Coan et al., 2003).These coefficients represent the average impervious values for each category nationwide. For developed, high intensity, it is 0.8503;for developed, medium intensity, it is 0.5768; for developed, low intensity, it is 0.2929; and for developed, open space, it is 0.0941.
In the High Resolution land cover data (island geographies) no coefficients were necessary. The area of the impervious class was simply summed and divided by the total area of the appropriate watershed and/or county.
How are development "gains" and "losses" defined in the Land Cover Atlas?
With respect to the Land Cover Atlas, a development "gain" occurs when either of the following criteria is met: (1) a pixel changed from a non-developed class in the early date to a developed class in the late date, or (2) a pixel that was mapped as a developed class in the early date changed to a greater intensity of development in the late date (e.g., developed, low intensity to developed, high intensity). Conversely, a development "loss" occurs when either of the following criteria is met: (1) a pixel changed from a developed class in the early date to a non-developed class in the late date, or (2) a pixel that was mapped as a developed class in the early date changed to a lower intensity of development in the late date.
References
Schueler, T. R., 1994. The importance of imperviousness. Watershed Protection Techniques, 1(3): 100-111.
Coan, M. J., B. K. Wylie, C. G. Homer, C. Huang, and L. Yang, 2003. An approach for mapping large-area impervious surfaces: synergistic use of Landsat-7 ETM+ and high spatial resolution imagery. Canadian Journal of Remote Sensing, 29(2): 230-240.
