Sentinel-1 reveals the dynamics of surface water connectivity across European wetlands

Wetland restoration in Europe under the EU Nature Restoration Law prioritises the recovery of surface water connectivity. However, our understanding of how water moves and connects in European wetlands remains limited, hindering effective restoration and monitoring. To address this, we first analysed changes in surface water extent across ~50 European Ramsar wetlands from 2015 to 2024 using Sentinel-1 data. Second, we developed a novel set of surface water connectivity metrics describing how water bodies emerge, merge, fragment, and persist through time. Quantification of these metrics revealed that ~80% of wetlands exhibit highly variable and unpredictable connectivity patterns across years. While surface water extent generally followed seasonal cycles, the timing of water-body merging and fragmentation diverged from water extent trends in many wetlands. In northern European wetlands, surface water connectivity was stable and predictable across years and closely linked to temperature and precipitation, reflecting strong seasonality and snowmelt regimes. In contrast, many central European wetlands showed irregular connectivity, with large interannual variability in water extent and connectivity often decoupled from simple seasonal wet–dry cycles. These patterns are likely shaped by the interaction of erratic temperature and precipitation, large upstream catchments, and human-modified floodplains. Our results demonstrate how satellite-based monitoring of surface water connectivity can be used to identify distinct hydrological regimes and evaluate future restoration efforts. Furthermore, given the strong heterogeneity in surface water connectivity across Europe, we suggest that restoration should not be evaluated using static extent-based indicators alone, but rather with multitemporal connectivity metrics that reflect how water actually moves and reorganises within wetlands.