Urban land-cover change analysis in Central Puget Sound

A methodology was developed to interpret and assess land cover change between 1991 and 1999 in Central Puget Sound, Washington at several scales (landscape, sub-basins, and 90 m grid window) relevant to regional and local decision makers. Land cover data are derived from USGS Landsat (Thematic Mapper and Enhanced Thematic Mapper +) images of Central Puget Sound. Landsat data were registered, intercalibrated, and corrected for atmosphere and topography to ensure accuracy of land cover change assessment. We apply a hybrid classification method to each image to address the spectral heterogeneity of urbanizing regions, The method combines a supervised classification approach with a spectral unmixing approach to produce seven classes: >75 percent impervious, 15 to 75 percent impervious, forest, grass, clear cut, bare soil, and water. Land cover change is identified using the direct spatial comparison of classified images derived independently for each time period. We assess that the overall accuracy of each classified image was 91 percent for 1991 and 88 percent for 1999 respectively, which produces an accuracy of 85 percent for the change analysis. Our results show that urban growth over the last decade has produced an overall 6.7 percent increase in paved area.