Dynamic indirect impacts of urbanization on vegetation growth in Chinese cities

Numerous studies have examined the potential impacts of urban expansion on vegetation growth. However, the impacts of urbanization on vegetation growth (Urb_i) across urban-rural gradients and its driving forces remain poorly understood. In this study, we used satellite observations of MODIS Enhanced Vegetation Index (EVI) from 2001 to 2019 to quantify the spatial–temporal dynamics of indirect urbanization impacts on vegetation growth and analysed their driving forces in 60 prefectural cities across China. The relationship between the Urb_i and urban intensity (β) was S-shaped, with a turning point where the indirect impact changed from negative to positive. The left-moving trend of the turning point in the southeastern cities indicated the expansion of areas with positive Urb_i during the last two decades. We further investigated the spatially heterogeneous effects of two natural and three anthropogenic driving factors on the Urb_i across the urban-rural gradient in different climate zones. The results showed that in temperate cities, as urban intensity increased, the presence of turning points was probably attributed to population increase. In cold cities, the change in the Urb_i was most likely induced by the enlarging population and increasing economic level from rural to urban areas. However, in arid cities, it was mainly determined by water supply and the cool island effect in urban cores rather than socioeconomic factors.