Assessing Long-Term and Seasonal Drivers of Black Sea Level Rise: Runoff and Loading Deformation (1993–2024)

Global warming and its associated impacts on sea level rise pose increasing risks to coastal regions. However, regional sea level changes are influenced by local factors, including land subsidence and localized climatic phenomena, which can exhibit significant variations that exceed the global average. As the world's largest inland sea, the Black Sea water level changes are driven not only by global climate processes but also significantly influenced by river runoff, with almost one-third of the entire land area of continental Europe draining into it, making it a critical factor in sea level variations. This study investigates long-term and seasonal variations in Black Sea water level and basin runoff by integrating satellite altimetry data with in situ hydrological observations, spanning 1993-2024. The results indicate a long-term sea level rise of 3.7 ± 0.38 mm/year for the Black Sea, with the winter season showing a notably higher trend of 3.89 ± 0.38 mm/year compared to other seasons. By investigating the relative contributions of steric (thermal expansion and salinity changes) and mass-related sea level changes, corrected for surface loading deformation, this study provides insights into the mechanisms driving regional sea level variability and the broader hydrological responses of Black Sea surrounding basins.

Keywords: the Black Sea; steric sea level rise; river discharge; Altimetry; loading deformation