Identification and comparative analysis of vegetation greening trends in built-up areas in China

Built-up areas are main places for human activities．Currently, we still lack a clear understanding of the spatiotemporal differences in greening trends between old and new urban areas within cities across China．Enhanced vegetation index from 2001-2020 was used in this study to analyze differences in greening trends between old and expanding built-up areas in China by Mann-Kendall test and Theil index．Approximately 20% (17 290 km²) of built-up areas in China were found to exhibit a significant greening trend; the East China-Central China wet-warm zone contributed 46.6% of the total greening area in China; more than 10% of the built-up areas in 30 provinces showed a significant greening trend．A comparison between older and expanding built-up areas found that older areas had become significantly greener, whereas the more recently expanded areas had become slightly greener; the greening area in older areas(13 474 km²) was 3.5 times that in the expanding areas(3 818 km²) ．Differences in the greening trend of vegetation in different climate change zones indicated that it is necessary to respond to the impact of climate change on the growth of vegetation in urban built-up areas locally, and pay attention to water supply facilities in the Southwest-South China dry-warm zone to meet the demand of vegetation growth．