Assessment of supply-demand relationships considering the interregional flow of ecosystem services.

Accurate assessment of ecosystem service (ES) supply, demand, and flow is essential for identifying and enhancing the ES supply-demand relationship and promoting regional sustainable development. Based on the InVEST model, supply-demand ratio, coupling coordination analysis, breakpoint and field strength model, and GIS spatial analysis method, we evaluated the supply and demand of water yield, food supply, carbon storage, and soil conservation service in the Loess Plateau in 2000 and 2020 and analyzed the supply-demand relationship before and after considering the interregional ecosystem service flow (ESF). The results showed that (1) from 2000 to 2020, the supply and demand of the four types of ESs in the Loess Plateau increased. Before considering ESF, the surplus degree in water yield, food supply, and soil conservation increased, and carbon storage decreased. In most counties, the coupling coordination between the supply and demand of the soil conservation is mostly extreme incoordination and moderate incoordination, and other types of ESs are mostly reluctant coordination and moderate incoordination. The degree of incoordination in water yield and soil conservation have eased, while food supply and carbon storage have strengthened. For the comprehensive supply-demand relationship of ES, the degree of surplus and coordination increased, with most counties were in a state of surplus and coordination. (2) Water yield and soil conservation services flow primarily to the western and northwestern portions of the Loess Plateau, with a decrease in the number of flow paths but an increase in the total flow rate for the former and a decrease in flow paths and total flow rate for the latter. The food supply and carbon storage flow in all directions and the total flow rate increases, with a significant increase in the number of flow paths for carbon storage. (3) After considering ESF, the supply-demand relationship of each type of ES and the comprehensive ES supply-demand relationship are changed, in which the degree of surplus and coordination of deficit counties are significantly improved, and some counties even become surplus or improve the level of coordination. After considering ESF, the supply-demand ratio changes even more relative to the degree of coupling coordination. This study is of great significance for identifying the cross-regional transfer pattern of ES, understanding in-depth the dynamic supply-demand relationship of ES, and mitigating the mismatch between supply and demand of ES. It provides a scientific and objective theoretical basis for promoting regional sustainable development.