How does urban expansion impact people's exposure to green environments? A comparative study of 290 Chinese cities

Understanding the difference of greenspace in different urban areas is a critical requirement for maintaining urban natural environment and lessening environmental inequality. However, how urban expansion impacts on people's exposure to ambient green environments has been limitedly addressed. Here we integrated multi-source geospatial big data including mobile-phone location-based service (LBS) data, Sentinel-2, and nighttime light satellite imageries to quantitatively estimate changes in people's exposure to green environments for 290 cities in China from 1992 to 2015. Results showed that the urban expansion process directly led to differences in green environments between old and new urban areas. These differences were not only observed by the green coverage rate but also captured using a dynamic assessment of people's exposure to greenspace. For most of China's large cities, people could enjoy more greenspace in new urban areas than the old ones. A significant day-to-night variation of people's exposure to greenspace was identified between old and new urban areas. Our results also revealed that urbanization did bring some positive effects to improve green environments for cities located in harsh natural conditions (e.g., semiarid/arid and desert regions).