Scalable Wetland Condition Monitoring With Harmonized Sentinel-2-Based Inundation Regime Indicators Across Europe

Reliable biodiversity reporting under the EU Habitats Directive and the Nature Restoration Law requires harmonized monitoring of hydrological dynamics across Europe’s (wet) grasslands and wetlands. Within the Biodiversa+ Habitat Pilot, we evaluated the scalability of Sentinel-2-based inundation models and the robustness of derived inundation regime indicators. We validated two inundation models across diverse European regions, achieving medium to high accuracy in open habitats (Macro-F1 between 0.64 and 0.93) but encountering limitations in densely vegetated areas and small, fragmented water bodies. To assess the reliability of long-term inundation regime monitoring for wetland habitat condition assessment, we conducted a sensitivity analysis. We quantified how different time series preprocessing decisions such as cloud filtering, temporal aggregation, and interpolation methods impact the indicator Mean Annual Inundated Fraction (MAIF). Our results indicate that this indicator is remarkably stable across various processing workflows variants, with site-specific ecological characteristics accounting for most of the variance. This suggests that simple, Sentinel-2-based inundation workflows can be sufficiently robust for large-scale reporting, provided they are adapted to local ecological contexts. For future research, we recommend exploring multi-class inundation classification or continuous soil moisture modeling to capture the finer ecological gradients in even more detail.