Identifying priority areas for freshwater supply conservation integrating multi-scale freshwater flows

Identifying priority areas for conservation is an effective measurement for the sustainable provision of ecosystem services (ESs) under threats globally. Although many approaches have been developed to identify conservation priority areas by combining supply and demand of ESs, the integration of ESs flows into the identification still need further exploration. For ESs like freshwater supply services, the processes of freshwater flows across multiple scales are crucial. This study aimed to propose a new study framework to identify priority areas for freshwater supply conservation by integrating the multi-scale (i.e., sub-watershed, tributary, and mainstream) freshwater flows, using the Yangtze River Delta as the study area. The results suggested that spatial mismatches between the supply and demand of freshwater supply services existed at different scales. There were approximately 129, 58, and 55 pairs of freshwater flows in sub-watersheds, tributaries, and mainstreams, respectively, which transported 5.98 × 10¹⁰ m³, 2.07 × 10¹⁰ m³ and 2.50 × 10¹⁰ m³ of freshwater. The results of multi-scale freshwater flows were integrated into conservation target goals, and the identified priority areas for freshwater supply conservation were selected at three scales. The priority areas selected at the sub-watershed scale were the largest. Compared with the traditional method of identifying priority areas without considering freshwater flows, the priority areas identified in this study included both sites with a high supply capacity and sites with a relatively low supply capacity, as they were significant for meeting the local freshwater demand. The increasing understanding of freshwater flows and the integration of the flows for the identification of priority areas for freshwater supply conservation are important for the development of more practical and rational policies or ecological management for the sustainable conservation of ESs.