Impacts of urbanization on net primary productivity in the Pearl River Delta, China

Great changes in land use/land cover from rapid urbanization have occurred in the PearlRiver Delta, China. As the primary cause of land development in the urbanization process,urban expansion has mostly occurred on land with higher NPP, significantly impacting theregional ecosystems. The primary purpose of this study was to reveal the impacts of urbanexpansion on the regional NPP. The land cover datasets and three types of urban lands (urban,peri-urban and non-urban areas) were obtained to quantify the urban expansion of the PearlRiver Delta from 2000 to 2010. The Carnegie-Ames-Stanford-Approach (CASA) model wasdriven by the land cover types, NDVI data and climate data to calculate the NPP for the studyarea and analyze its spatial-temporal variations, as well as the impacts on NPP from urbanexpansion. The results showed: cropland and forest with higher NPP values and wetland werethe major source of urban expansion, which generally reduced the regional NPP values,primarily by replacing vegetation with urban land. The conversion of land to urban use resultedin a reduction of 0.103TgC from 2000 to 2005 and 0.034TgC from 2005 to 2010, cropland andforest accounted for the largest proportion of the total NPP losses. In spatial distribution, theNPP losses occurring in urban and peri-urban areas accounted for 89.63% and 75.04%,respectively, which was primarily a result of the massive vegetation with high productivitybeing replaced with impervious surfaces during the rapid urbanization process. These resultsprovided an indicator to understand and evaluate ecosystem changes in urban regions.