Climate trends in the Azerbaijani Caspian Sea sector and associated atmospheric circulation indices

This study analyzes recent climatic changes in the Azerbaijani Sector of the Caspian Sea (ASCS) and their relationships with large-scale atmospheric circulation. Long-term changes in meteorological variables, river runoff, and sea level were assessed using data from 33 hydrometeorological stations and gauging posts for 1981–2024. Trends were evaluated using the Mann-Kendall test and Sen’s slope estimator, while atmospheric circulation was examined using the Vangengeim-Girs classification and North Atlantic Oscillation (NAO) index. The results indicate significant regional warming, with a mean annual air temperature of approximately 14.0 °C and an increase of 1.6 °C over the study period (Sen’s slope: +0.036 °C/year). Summer warming was particularly pronounced, reaching 0.73 °C/decade in Baku, while August temperature anomalies reached +1.5 °C relative to the 1961–1990 baseline. Total river runoff decreased by 24% (115.5 m³/s) during 1991–2024 compared with 1961–1990, coinciding with persistent sea-level regression. GIS-based analysis indicates that shoreline retreat exposed approximately 1,371.7 km² of coastal land, about 60% of which has become stable dry surfaces. Correlation analysis suggests that sea-level variability is associated with large-scale circulation: E-type circulation correlates negatively (r = −0.62 to −0.67), whereas W-type circulation shows a positive correlation (r = 0.69–0.77).