Quantifying spatiotemporal patterns of urban impervious surfaces in China: An improved assessment using nighttime light data

Quantifying the spatiotemporal patterns of impervious surfaces (ISs) is crucial for assessing the environmental impacts of urbanization. Nighttime light (NTL) data provide a new way of mapping urban IS on broad scales. However, the accuracy of this approach is currently low and thus further improvements are much needed. Here we have estimated the urban IS dynamics of China from 1992 to 2009 using the Vegetation Adjusted NTL Urban Index (VANUI), which combines NTL and Normalized Difference Vegetation Index (NDVI) data. With VANUI, we were able to quantify the spatiotemporal patterns of IS in China with a much higher accuracy than previous methods. Key to this improvement was VANUI's ability to alleviate the problem of saturation inherently associated with NTL data. Our study shows that the total urban IS area of China increased substantially from 10,614.23 km2 in 1992 to 31,147.63 km2 in 2009, at an annual increase rate of 6.54%. China's urban IS expansion exhibited pronounced regional differences, with six large “hotspot” areas where urban IS expanded most substantially. These hotspot regions accounted for 0.87% of China's total land area, but 37.66% of the total area of urban IS expansion during 1992-2009. Measures of urban IS are not only important for characterizing urbanization patterns and processes, but also essential for assessing ecological and environmental impacts of urbanization. Our results provide a valuable dataset and new insights for better understanding the speed and scope of China's recent urbanization, as well as for designing and developing sustainable cities in China and beyond.