Monitoring the dynamics of the Danube islands system, using SAR imagery (Orșova–Vedea sector, 1992–2022)

The Danube and its islands play a pivotal role in maintaining the ecosystem balance in the region. Anthropogenic activities over the past century, combined with extreme natural events, such as floods, interact in synergy and can significantly influence the dynamics of the islands. This includes the appearance or disappearance of islands, changes in their surface area, length, shape, number, and so forth. The objective of this work is to catalogue, study, and monitor the evolution of islands within a 445.29 km stretch of the Lower Danube River, between Orşova and Vedea. These are two Romanian localities situated at the confluence with the Cerna and Vedea rivers, respectively. For this study, we utilized SAR (Synthetic Aperture Radar) images captured on various dates to identify the existing islands. After mapping each island and sub-island, we calculated their respective morphometric parameters and compared them. The results reveal a decrease of 12 islands and/or sub-islands, resulting in a total of 74 islands identified in 2022 with a combined area of 147.63 km 2 , in contrast to 86 in 1992 with a total area of 154.29 km 2 . Over this 30-year span, we have estimated an average reduction rate of approximately 0.22 km 2 /year, with an annual “de-sedimentation” rate of around 0.14%. This accelerated dynamic stems from extreme meteorological events, exacerbated by human activities, amplifying the hydromorphological processes—especially in areas sensitive to water level variations, slope fluctuations, and “de-sedimentation”.