Spatio–Temporal Variations in Impervious Surface Patterns during Urban Expansion in a Coastal City: Xiamen, China

Impervious surfaces (IS) coverage is a quantifiable environmental indicator for understanding urban sprawl and its potential impacts on sustainability of urban ecological environments. Numerous studies have previously demonstrated global and regional IS variation, but little attention has been paid to the different internal and external patterns of IS development as urbanization progresses. This study estimates IS coverage in a subtropical coastal area of Xiamen, southeastern China, from Landsat TM/OLI images obtained in 1994, 2000, 2004, 2010, and 2015, and quantifies its spatio–temporal variations using IS change trajectories and radar graphs. During the study period, IS gradually expanded along the shoreline in a pattern resembling the shape of the bay. The land surfaces are classified into four zones: IS1 and IS2, dominated by cultivated land and forest; IS3, complex land use/coverage; and IS4, built-up areas. The progression and transformations of these zones highlight the main trends in IS changes in the study area. The trajectories of the zones form a layered structure in which the urban centers of each district progressively gain IS4, and transformations into IS3 and IS2 extend successively beyond the centers. The orientation of IS expansion in each of the six districts of Xiamen is revealed by radar graphs. The areas containing intermediate and high percentages IS each expanded in generally consistent directions throughout the study period, except in Tong’an district, which showed a change in the direction of expansion of its area of intermediate and high IS