Spatiotemporal dynamics of water extent, level, and storage of lakes with contrasting bathymetries: insights from the Trichonida – Lysimachia lake complex in Western Greece

Accurate spatiotemporal monitoring of inland water bodies is crucial, since, apart from numerous ecosystem services they also provide valuable water resources. This is particularly true in water-limited Mediterranean regions where detailed characterization of lake water extent, level and storage could facilitate sustainable water resources management under climate extremes (e.g., droughts). Here, focusing on the Trichonida – Lysimachia lake complex in Western Greece, we synthesized remote sensing observations, in-situ measurements, and auxiliary environmental and geospatial datasets, in order to characterize the spatiotemporal dynamics in their water extent, level, and storage. The Trichonida – Lysimachia lake complex is a sensitive ecosystem, protected as part of the Natura 2000 network; lake Trichonida is the largest natural lake in Greece (surface area of ~93 km² and maximum depth of ~52 m) and is connected through an open channel with the much smaller and shallower lake Lysimachia (surface area of ~10 km² and maximum depth of ~8 m). The analysis of optical (Landsat 5, 7, 8, 9, Sentinel 2) and microwave (Sentinel 1) satellite imagery revealed that both lakes displayed significant changes in their areal extent at the seasonal and annual time scale, with these results being more pronounced for the lake with shallower bathymetry (i.e., Lysimachia). The surface area of lake Trichonida (Lysimachia) decreased significantly during the period 1985 – 2024 at a rate equal of 32.3 m² yr^-1 (36.4 m² yr^-1) with hotspots that displayed more than 100 m shift in the shoreline. In-situ water level measurements agreed well with estimates from satellite altimetry (ICESat, SWOT), and, when combined with the detailed bathymetries of the two lakes, detailed water level-area-volume curves were derived. Such curves, synthesize multivariate observations, in-situ measurements, and cross-disciplinary hydrogeodetic techniques and reveal lake-specific 3D patterns. The obtained results offer valuable insights not only towards the sustainable management of the two lakes but can also contribute to the refinement of regional- and global-scale initiatives on satellite-based 3D lake monitoring.