Assessment of water quality and coastal changes under climate impacts using multi-sensor satellite techniques in the...

The southern Absheron Peninsula is experiencing increasing ecological stress caused by both climatic shifts and anthropogenic pressures. Using multi-sensor satellite data, we estimated water quality indicators Chlorophyll-a (Chl-a), Trophic State Index (TSI), Colored Dissolved Organic Matter (CDOM), and Land Surface Temperature (LST) for 2021-2025. An investigation of water quality in the research area was conducted using Sentinel-2 optical data and processed with Google Earth Engine (GEE) from 2021 to 2025. The integration of remote sensing and cloud-based processing provides a practical framework for long-term monitoring, supporting data-driven decision-making for sustainable coastal management. To explore the physical drivers underlying these ecological changes, ICESat-2 ATL03 photon data were used to evaluate vertical seafloor changes along a fixed coastal track. This shoaling is attributed to sediment accumulation or coastal infilling, likely linked to reclamation activities and altered hydrodynamic conditions near the Zigh shoreline. The surface temperature displayed warming in summer most surpassing 30 °C, overlapping with higher Chl-a and TSI values and highlighting the role of temperature in intensifying eutrophication risk. Land reclamation along the Zigh and Hovsan coastline decreased water circulation, resulting in the boosting of CDOM and Chl-a accumulation. We complemented this with ICESat-2 photon-based bathymetry estimation and GRACE/GRACE-FO sea level observations. ICESat-2 bathymetry analyses approved significant nearshore bathymetry changes, with depths decreasing from ~7 m (2020-2021) to 2-3 m in 2024, reflecting sedimentation and shoreline transformation. GRACE/GRACE-FO observations of sea-level decline reinforce the combined influence of hydrological change, sediment redistribution, and human-driven alterations on coastal morphology. Results underscore the pressing nature of the situation, with climate-driven sea-level decline, rising temperatures, and local anthropogenic activities jointly degrading water quality and reshaping bathymetry in the southern Absheron Peninsula. This integrated approach highlights the urgent need for enhanced wastewater management and sustainable coastal planning to protect the Caspian Sea's ecosystems.