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• Recorded changes in UGS in 107 Chinese cities reveals the process and drivers. • NUDI is a novel indicator to quantify and map built-up areas. • Proposed RGDI can be used to better quantify regional UGS dynamics. • Long-term built-up urban areas have become greener in the last decade. • Greening in long-term built-up area in the past decade is underlain by economic. Urban green space (UGS) has gained increasing attention due to its environmental and social functions. However, the compound effects of climate change, population growth and economic development on UGS are largely unknown. We selected 107 medium-sized and large cities in China to investigate dynamics in the spatial pattern of UGS in relation to government policy and other drivers based on remote sensing data for the period 1990 to 2019. To explore the effect of different levels of urbanization on changes in green space, we develop a new Normalized Urban Development Index (NUDI) to classify urban-suburban-rural gradients, viz. Long-term Built-up, New Built-up and Non-Built-up. Then, we analysed changes over time in the annual peak value of fraction of vegetation cover (FVC) for 380,000 cloud-free Landsat images, and regional UGS dynamics were evaluated using the proposed Regional Greenness Dynamic Index (RGDI). Finally, to reveal the major driver(s) of changes in UGS and estimate the extent to which patterns of urban greening are due to differences in economic development, we compared the observed UGS spatio-temporal dynamics with data on several climatic, social-economic and land use related factors for the same period. The NUDI are shown to be highly effective in mapping urban development gradients, with overall accuracy in the identified classes of 89%. Annual maximum FVC analysis indicates that there was significant greening between 1990 and 2019 in both the long-term built up (10,667.52 km 2 ) and the non-built up areas (529,310.47 km 2 ), while there was a major increase in browning (25,110.43 km 2 ) in the newly built-up areas. The RGDI results indicate that 65% (71/107) of long-term built-up areas in cities trended greener over 2010 to 2019 under consideration. At the whole city scale, RGDI is negatively correlated with gross domestic product (GDP), although when considering the long-term built-up areas only, economic growth exhibits a significant positive correlation during 2010 to 2019 (R = 0.62, p < 0.01). This study offers important insights as to the patterns of change in urban greening extent over time and its underyling drivers across urban-suburban-rural gradients against the background of urban expansion, afforestation, climate change and economic development.
Wu et al. (Fri,) studied this question.