A land-cover-based approach to assessing ecosystem services supply and demand dynamics in the rapidly urbanizing Yangtze River Delta region

It is essential to appraise the impacts of land use and cover change on both the supply and demand sides of ecosystem services to formulate effective land use policies towards sustainable development. However, it remains challenging to accurately quantify ecosystem services supply and demand with comparable measurement units. Burkhard et al. (2012) proposed the use of an expert-based matrix model to assess ecosystem services supply and demand per land cover class in comparable semi-quantitative units. In this study, we improved the matrix model by measuring the levels of uncertainty that arise from expert estimation to obtain more accurate estimates, and by proposing a more adequate synthesis method to create the comprehensive index for quantifying ecosystem services supply-demand budgets with semi-quantitative estimates in the matrices. Taking the rapidly urbanizing Yangtze River Delta (YRD) region of China as an example, we used the improved matrix model to characterize relative changes in ecosystem services supply and demand in response to land use and cover change during 1985-2015. According to our land-cover-based matrix model, the two dominant land cover types (built-up area and rice fields) in the four largest cities (Shanghai, Nanjing, Hangzhou, and Suzhou) of the YRD region all exhibited greater demand for freshwater, flood protection, water purification, and erosion regulation than the provision of these hydrological services. Consequently, the four cities also exhibited greater demand for these four hydrological services than the supply of these services from local ecosystems. During the past three decades, the built-up area of the four largest cities expanded by 2.2-4.9% annually, along with an annual decrease rate of 1.9-4.6% for croplands (including rice fields and rainfed croplands). The rapid urban expansion and the huge loss of croplands caused the supply-demand budget index value of food production service to decrease by 1.7-3.7% annually, indicating large decreases in the provision of food production service, alongside large increases in food demand. Among the three categories of ecosystem services, the regulating services were in severe short supply for the four largest cities of the YRD region, while the cultural services were in sufficient supply during the past three decades. In contrast, the provisioning services shifted from sufficient supply in 1985 to insufficient status in 2015, primarily due to the rapid urban expansion. Our results illustrate clear and direct impacts of urban encroachment on both the supply and demand sides of multiple ecosystem services. This improved matrix model can be applied to assess ecosystem services supply and demand dynamics for other rapidly urbanizing regions.