Coefficient-based consistent mapping of imperviousness in the conterminous U.S. at 60-m resolution for 1974, 1982, 1992, 2002, and 2012

Anthropogenic impervious surfaces affect hydrology, water quality, and ecological health and are widely studied. Previous studies have been limited, however, by a lack of consistent representation of imperviousness nationally as a time series prior to 2001. This product presents estimated imperviousness at 60-meter spatial resolution, for the time periods 1974, 1982, 1992, 2002, and 2012. The mapping was derived by comparing imperviousness from the National Land Cover Database (NLCD) 2011 to national land use from the 2012 U.S. Geological Survey NAWQA Wall-to-wall Anthropogenic Land Use Trends (NWALT) product. The NWALT land use product includes a series of 60-m national rasters, containing 18 land use classes, for five time periods from 1974-2012. Coefficients of imperviousness were derived for each land use class for 2012, and then re-mapped back to the NWALT previous eras of 2002, 1992, 1982, and 1974. The impervious mapping is facilitated by the 7-class urban detail of the NWALT land use product. Coefficients were derived for each of 909 Census Core-Based Statistical Areas (CBSAs) in the conterminous U.S., and were thus tailored to the characteristics of specific metropolitan and rural areas. When measured over HUC-12 watershed areas, the coefficients provided very similar 2002 imperviousness estimates to those from the 2001 NLCD: r2 (RMSE) of 0.93 (0.6), and 96% of HUC-12s mapped to within 1% of their actual imperviousness value. The resultant rasters provide a tool from which consistent measurements of imperviousness can be made for zonal or watershed areas in the conterminous U.S. for the last 4 decades.

人为不透水面（anthropogenic impervious surfaces）会对水文过程、水质及生态健康造成影响，相关研究已得到广泛开展。然而，此前的研究受限于2001年之前缺乏全国范围的不透水面时间序列统一表征方案。本数据集提供了1974年、1982年、1992年、2002年与2012年五个时段、空间分辨率为60米的不透水面估算结果。该制图产品通过对比2011年全国土地覆盖数据库（National Land Cover Database, NLCD）的不透水面数据，与2012年美国地质调查局（U.S. Geological Survey, USGS）NAWQA全覆盖人为土地利用趋势（NAWQA Wall-to-wall Anthropogenic Land Use Trends, NWALT）产品的全国土地利用数据生成。NWALT土地利用产品包含1974年至2012年五个时段的一系列60米分辨率全国栅格数据集，涵盖18类土地利用类型。研究人员针对2012年的每一类土地利用类型推导了不透水面系数，随后将其回溯映射至NWALT产品的2002年、1992年、1982年及1974年四个历史时段。NWALT土地利用产品的7类城市细分类型为不透水面制图提供了支撑。研究人员针对美国本土的909个人口普查核心统计区（Census Core-Based Statistical Areas, CBSAs）分别推导了不透水面系数，从而实现了针对特定大都市区与农村地区的定制化适配。以HUC-12级流域（Hydrologic Unit Code 12, HUC-12）为验证单元时，该系数得到的2002年不透水面估算结果与2001年NLCD的结果高度吻合：决定系数（均方根误差）为0.93（0.6），且96%的HUC-12流域的估算不透水面值与实际值的偏差在1%以内。最终生成的栅格数据为量化美国本土近40年的区域或流域不透水面提供了统一的标准化工具。