Multi-scale supply-demand security assessment of water-energy-food related ecosystem services from an interaction perspective

Ensuring supply-demand security of the water-energy-food (WEF) nexus is vital for balancing socio-economic development and natural ecosystems. However, existing studies often focus on single-scale assessments within individual units and overlook cross-regional interactions. To address this gap, this study develops a multi-scale framework integrating ecosystem services (ESs) as a common lens to capture both intra-regional supply-demand balances and inter-regional interactions. Taking the Yangtze River Delta (YRD) as a case study, we quantified the supply and demand for water yield (WY), carbon sequestration (CS), and food provision (FP) in 2000, 2010, and 2020 using the InVEST model, remote sensing products, and socio-economic statistics. By applying the supply-demand index (SDI), coupling coordination degree (CCD) model, gravity model, and network analysis, we evaluated WEF supply-demand security across provincial, municipal, and county scales. The framework revealed four coupling types that combine intra-regional supply-demand status with inter-regional network importance. Results show that mismatches were widespread, with many units exhibiting strong internal provisioning but limited external interactions. These imbalances became more pronounced at finer scales, as county-level analysis revealed structural divergences often masked in provincial summaries. These insights underscore the utility of the framework in diagnosing cross-scale imbalances and in guiding regionally tailored, multi-level policy responses for improving WEF-Nexus related ESs security.