Decadal changes in meteorological extremes and environmental consequences in the Caspian Sea Region

Abstract Using data from the MERRA-2 database, the study identifies a clear warming trend in August, with significant peaks in the annual average air temperature in 2010 (28.3 °C) and 2021 (27.9 °C) in the Caspian Sea. Concurrently, the Caspian Sea’s water levels have declined by approximately 16 cm annually from 1992 to 2025, totaling a drop of around 2.04 m, driven by higher evaporation rates linked to rising temperatures. Heat extremes are observed, with maximum daily air temperatures reaching 30.3 °C and minimums of 26.8 °C in August 2021, representing deviations of 2.6 °C and 2.4 °C from the climatological mean. The most intense event exceeded 2.63 °C for the maximum 2 m air temperatures in August 2021 and 2.16 °C above the climatological mean for an extended 12 days. Furthermore, the frequency of heatwaves has increased, with two major heatwave events occurring in 2010 and 2021. The study also highlights significant changes in sea surface temperature, Chlorophyll concentrations, and sea salt levels, with higher sea salt concentrations in 2021 correlating with lower Chlorophyll levels. Spatial analysis reveals regional temperature variations, with warmer temperatures in the southeast in 2010 and cooler conditions in the eastern regions in 2021. Additionally, the study observed a shift in the subtropical jet stream, which weakened and shifted eastward in 2021 compared to 2010. The jet stream split around the high-pressure system, transitioning from zonal to meridional flow. These changes in atmospheric circulation, characterized by dry conditions and reduced low-level relative humidity in 2021 (5–10% drier than in 2010), contributed to the extreme heatwave events. The findings highlight the role of atmospheric circulation patterns, including the development of high-pressure systems and shifts in the jet stream, in driving temperature extremes and heatwaves in the Caspian Sea region, with significant implications for future climate variability and ecosystem impacts. The results underline the need for further research and mitigation efforts to address the ongoing warming, heatwaves, and water level decline in the Caspian Sea, which pose significant ecological and socio-economic challenges. Marine heatwaves in the Caspian Sea have been causing significant ecological disruptions.