Is Climate Forcing Alone Sufficient to Explain the Decline of the Caspian Sea Level? Space-Geodetic Evidence of Tectonic Deformation Along the Neftchala-Lankaran Coast of Azerbaijan

The Caspian Sea has experienced an accelerated decline in water level over the recent decade, leading to obvious shoreline retreat, ecosystem stress, and increasing socio-economic impacts along coastlines. While climate-driven factors such as rising air temperature, enhanced evaporation, and changes in regional hydrology are widely recognized as primary drivers of this decline, the potential contribution of tectonic processes remains insufficiently explored. This study investigates the interaction between Caspian Sea level change and coastal dynamics, with a particular focus on the role of tectonically driven vertical land motion along the coastline. Using multi-temporal InSAR analysis of Sentinel-1 data between 2014 and 2025, we quantify coastal vertical deformation patterns across key sectors of the Caspian shoreline, including areas affected by subsidence, uplift, land reclamation, and rapid shoreline migration. These deformation signals are analyzed together with observed coastline changes derived from optical satellite imagery, enabling the separation of relative sea-level effects from absolute water-level variations. Preliminary results reveal spatially heterogeneous deformation along the coast, with localized uplift and subsidence rates that are comparable in magnitude to the observed rate of sea-level decline. In some regions, shoreline retreat coincides with uplifted coastal segments, suggesting that tectonic processes may amplify the apparent rate of relative sea-level fall.
The findings show that Caspian Sea coastal changes cannot be completely clarified by climatic forcing alone, and that both tectonic deformation and broader geodynamic processes contribute to the observed sea-level and shoreline trends. This study demonstrates that climate forcing alone is insufficient to explain the decline of the Caspian Sea, highlighting the role of tectonic deformation along the coast. Integrating geodetic deformation measurements with coastal change analysis provides independent evidence of vertical land motion influencing relative sea-level and shoreline trends, with important implications for hazard assessment, coastal management, and future projections under ongoing climate change.