Changes of ecological vulnerability in areas with different urban expansion patterns- A case study in the Yanhe river basin, China.

Urban expansion has the potentiality to disrupt ecosystems and form highly fragile urban landscapes. However, studies investigating the impact of different urban expansion patterns on the ecological environments are relatively limited. Taking the Yanhe river basin, a typical basin in a loess region, as a case study, we developed an ecological vulnerability assessment system as well as assessed the main drivers of ecological vulnerability for different time periods (1990, 2000, 2010 and 2018). Additionally, we classified each urban expansion region into three different patterns according to the landscape expansion index, and analyzed changes in the ecological vulnerability under these three diverse patterns. Finally, the Kruskal-Wallis rank sum test was applied to compare the factors for the different changes in ecological vulnerability across different urban expansion patterns. Our investigation also aimed to elucidate the impacts of different urban expansion patterns on ecological vulnerability and identify key physical-social-economic-climatic drivers. The results indicate that the ecological vulnerability index (EVI) of the study area is decreasing gradually from the peak value of 0.459 in 2000 to 0.383 in 2018. Habitat quality index is found to be the most influencing factor, followed by aridity index and building density (mean q of 0.53, 0.46, and 0.42, respectively). Our study also reveals that the outlying expansion areas have the greatest increase in EVI at 0.38, with edge and infill expansions at 0.31 and 0.27, respectively. It is also found that when the overall environment is improving, the outlying expansion areas have the smallest decrease in EVI. Initial ecological vulnerability and key drivers may explain this difference. Therefore, results of this study indicate that the ecological impacts of diverse urban expansion patterns are significantly different, among which outlying expansions should receive prioritized attention.