Hydrological Regime Alteration and Progressive Degradation of Anzali Wetland in Response to Caspian Sea Level Decline

Wetlands are among the most sensitive coastal ecosystems, where water level variations rapidly induce structural and qualitative changes. This study investigated changes in water surface area, water level, and water quality of the Anzali Wetland during 2000–2025 using multi-source remote sensing data, including MODIS, Landsat 8, Jason-2, and Sentinel-6. Statistical relationships between wetland area, Caspian Sea Water Level (CWL), Tm, and Rainfall were analyzed using linear, rank-based, nonlinear, and K-means clustering approaches. The results showed that CWL declined by more than 2 m over the study period, decreasing from − 26.5 in 2000 to − 28.6 m in 2025. Concurrently, the water surface area of the Anzali Wetland decreased sharply from 38.26 to 8.27 km2, indicating a loss exceeding 78