Urban environmental quality of shrinking cities in China improved less than that of non-shrinking cites during 2000-2020: A quantitative comparison based on propensity score matching method

Abstract

Shrinking cities face challenges such as underutilized resources and environmental changes in light of declining disturbance of anthropogenic activities and lack of financial support. In this context, the evolution of their environmental quality must be analysed timely and effectively. This study aimed to investigate the spatiotemporal changes in the environmental quality of shrinking cities in China from 2000 to 2020, and compared the changes between shrinking cities and non-shrinking cities. We leveraged the Google Earth Engine platform to analyse the spatiotemporal changes in the environmental quality of shrinking cities in China over the past two decades, based on the comprehensive environmental index (CEI). Then, we applied the propensity score matching method to match shrinking cities with comparable non-shrinking counterparts for comparative analysis. We evaluated the effects of policy interventions by combining the Difference-in-Differences (DID) model and the synthetic control method (SCM). The findings showed that the environmental quality of shrinking cities follows a U-shaped trajectory. From 2000–2007, the environmental quality of shrinking cities decreased, followed by a substantial improvement after 2013. Over the past 20 years, the CEI of shrinking cities has increased by 5.70 %, which was slightly lower than the 6.89 % increase observed for non-shrinking cities. Specifically, shrinking cities in northern China exhibited the highest environmental quality and the highest improvement rate (5.99 %), whereas those in the southern, northwestern, and Qinghai‒Tibet regions exhibited modest improvements (increases of 5.34 %, 4.65 %, and 5.32 %, respectively). The decrease in PM_2.5 concentration was the main contributing factor to the improvement of environmental quality. Policy analysis showed that environmental policies such as the "Air Pollution Prevention and Control Action Plan" had a significant promoting effect on improving the environmental quality of shrinking cities. To promote sustainable development, it is vital to formulate targeted and regional-specific environmental improvement policies for shrinking cities.