Effects of multi-gradient urbanization and climatic drivers on EVI in the middle Yangtze River Basin, China

Abstract

Comprehending the asymmetric response of urbanization to vegetation growth is crucial for optimizing regional resource allocation. The enhanced vegetation index (EVI) is commonly utilized to monitor vegetation growth. However, the mechanisms driving vegetation growth across various urban gradients remain ambiguous. In this study, we developed a theoretical framework spanning city boundaries to analyze the response of urbanization to vegetation growth. Additionally, we quantified the contribution of meteorological drivers. The results showed that (1) the variability of impervious surface area (ISA) across urban boundaries is significantly higher than in the entire study area. In the new urban area (N-UA), the percentage of ISA increased from 31.58 to 70.08% between 1990 and 2018; (2) the cubic curve fitting degrees all exceeded 0.84. EVI demonstrated significant enhancement over time within each urban gradient, and the closer the impervious surface proportion (ISP) was to 1, the more pronounced the difference in EVI; (3) the indirect impacts of urbanization increasingly offset the direct impacts as the ISP gradient rises, reaching a peak at a certain point before slightly diminishing; (4) average downward surface shortwave radiation and NO₂ were the most significant contributors to vegetation enhancement in the old urban core. Temperature also played a major role, particularly in the new urban core and N-UA areas. Our research provides novel insights into the large-scale dynamic response of vegetation growth to urbanization.