The imprint of urbanization on vegetation in the ecologically fragile area: A case study from China's Loess Plateau

Rapid urbanization significantly affects vegetation growth in urban environments. Responses of vegetation to urbanization at high spatial resolutions and long temporal ranges are still unclear, especially in ecologically fragile areas. Here, we explored urbanization impacts on vegetation across China's Loess Plateau (CLP) from 2000 to 2020 at a spatial resolution of 30 m. Urbanization and annual maximum Normalized Difference Vegetation Index (NDVI) in urban agglomerations, provincial capital cities, also the whole CLP experienced a rapid increase over this period; the annual maximum NDVI (NDVImax) in urban areas decreased before 2011 but increased afterward to reach its maximum value in 2018, and in non-urban areas, a significant increase was found between 2000 and 2020. NDVImax with significant reduction areas were mostly distributed in the urbanization area. A total of 97.56%, 53.66%, 80.49%, and 100% of all cities' urban core, urbanization, urban, and non-urban areas, respectively, indicated an increase in NDVImax during 2000-2020. For 97.56% (40/41) of the cities in the CLP, the increases in NDVImax in the non-urban areas were stronger than the NDVImax increases detected in the urban areas of these cities. In general, the urban areas of most cities (29/41) in the CLP had positive NDVI trends of greater than 50%. The NDVImax generally decreased with increasing urbanization development intensity (UDI) in 2000 and 2020 in the CLP along with five urban agglomerations. These findings have important implications for understanding urbanization impacts on vegetation, urbanization management, and development in ecologically fragile areas.