Evaluation of ecosystem services budget based on ecosystem services flow: A case study of Hangzhou Bay area

Ecosystem services (ESs) flow, the spatial transfer of ESs from supply to demand, is critical but remains underexplored. Traditional studies often quantify ESs flow by crudely overlaying supply-demand, which lacks authenticity. This work develops a simulative model based on the flow-medium-path agent to simulate and quantify ESs flow, and subsequently evaluate regional ESs budget by incorporating ESs flow, because ESs aren't static but could flow to remote area, thereby altering the supply-demand relationship. Three prominent ESs, crop production (CP), water yield (WY), and carbon sequestration (CS) in Hangzhou Bay area were selected as cases. The results show: (1) a noticeable mismatch between ESs supply and demand; (2) ESs flow appears diverse features, e.g., the WY flow is single-directional and can only deliver to the downstream, determined by the topography; (3) Traditional ESs budget reveals the number of towns as supply exceeding demand for CP, WY, and CS is 313, 411, and 171. Contrastively, regional final budget considering ESs flow suggests that is 202, 581, and 0 as supply-demand balanced, indicating the ecological state is altered by integrating ESs flow into ESs budget evaluation. This study contributes to the researches on ESs comprehensive evaluation, ESs flow quantification, and ecological strategies references.