In this study, spanning from 1938 to 2020, the hydrological changes in the Volga River and their repercussions on the Caspian Sea level were examined. Analysis reveals a correlation between high Volga River runoff and increased atmospheric precipitation in its basin. However, in recent years (2005–2020), a significant decline in the runoff coefficient at the Verkhneye Lebyazhie hydrological station, attributable to climate warming surpassing global temperature anomalies, has been observed. This warming’s impact on river flow and sea level was quantified, resulting in a 133 cm decrease in sea level from 1977 to 2020. Notably, while, historically, Caspian Sea level changes mirrored Volga River runoff fluctuations until 2005, since 2006, the sea level has markedly dropped, decoupling from river runoff variations. Comparison with recent studies suggests that altered wind characteristics over the Caspian Sea, influencing surface evaporation, may have significantly contributed to this rapid sea level decline in recent years.

This study investigates changes in the wind regime over the Caspian region and their impact on sea level fluctuations, utilizing MERRA-2 reanalysis data spanning the period 1980–2023. The analysis revealed no statistically significant variation in average wind speed between the phase of sea level decline (2005–2022) and the preceding phase of sea level rise (1984–2004). However, more detailed examination of specific wind parameters indicated notable shifts: the speed of resultant winds increased by 10.3%, accompanied by a 9.5° change in predominant wind direction, as derived from eastward and northward wind vector components. Furthermore, comparison of resultant wind characteristics with key climatic indices—specifically the Southern Oscillation Index (SOI) and the North Atlantic Oscillation (NAO)—demonstrated a moderate relationship between wind regime variability and sea level dynamics, including interannual fluctuations. These findings underscore that sea level changes in the Caspian Sea are closely linked to climate variability, mediated in part through alterations in regional wind patterns.

In this article, we studied the upwelling phenomena observed in the surface waters of the Caspian Sea. Studying upwelling is crucial for understanding and managing the complex interactions between the ocean, climate, and marine life, with implications for both environmental conservation and human well-being. To accomplish this, we utilized data from MODIS-Aqua satellite observations in the infrared range of 11 microns. These observations had a spatial resolution of 4 km and covered the period from 2003 to 2021. The data was accessed through the NASA Giovanni online data system databases. Our findings indicate that upwelling phenomena are primarily observed in the eastern part of the Middle and South Caspian from May to September. The most intense upwelling occurs along the eastern coast of the Middle Caspian in July and August. Based on long-term averaged data, the upwelling phenomenon is typically observed between 40-44º latitude during this period. The width of the upwelling zone increases gradually from north to south, extending approximately 60-70 km towards the Kazakh Gulf before decreasing towards the south. In the upwelling zone, the temperature gradient can at times reach 4.0ºC per 100 km. In certain years, the upwelling zone that initially forms along the eastern coasts can extend over long distances and even reach the western coasts. Generally, the upwelling phenomenon occurs alongside the advection of warm waters from the South Caspian towards the Middle Caspian.

Plastic pollution poses a major environmental threat to coastal ecosystems, particularly in enclosed and semi-enclosed seas where limited water exchange promotes debris accumulation. This study presents a high-resolution spatial analysis of coastal plastic debris along the Khachmaz coastline in the western Caspian Sea. The analysis integrates unmanned aerial vehicle (UAV) imagery, YOLO-based deep learning detection, and spatial statistical methods. High-resolution UAV orthophotos enabled the automated detection of individual plastic debris items, which were converted into spatial point data for further analysis. Spatial patterns were assessed using areal density estimation, nearest neighbor analysis, kernel density estimation, and Ripley’s L-function to examine clustering across multiple spatial scales. A total of 2389 plastic debris items were identified within 0.0439 km², corresponding to an average density of 54,382 items per km². The results show that plastic debris is unevenly distributed, forming distinct clusters with four primary accumulation hotspots. Significant clustering occurs at spatial scales up to 20 m, with the strongest aggregation observed at distances below 5 m. Spatial overlay analysis indicates a strong association between plastic debris, reed-dominated coastal vegetation, and proximity to the shoreline, suggesting the potential role of localized retention processes and shoreline dynamics in debris accumulation. The combined use of UAV-based deep learning and spatial statistical analysis provides an integrated application framework for monitoring coastal plastic debris and supports targeted, sustainability-oriented coastal management strategies in the Caspian Sea region.

The Caspian Sea is the largest enclosed water body on Earth, and it is undergoing rapid fluctuations in water level that pose significant risks to ecosystems, infrastructure, and socio‑economic activities across its littoral states. This study integrates hydrological and atmospheric perspectives to identify the primary drivers of recent and projected sea level changes.Long‑term hydrological records (1938–2020) from the Volga River, the dominant freshwater contributor, reveal a strong historical correlation between high runoff and increased atmospheric precipitation in its basin. However, since 2005, a marked decline in the runoff coefficient at the Verkhneye Lebyazhie hydrological station has been observed, attributable to regional warming that exceeds global temperature anomalies. This decline contributed to a 133 cm reduction in Caspian Sea level between 1977 and 2020. Importantly, while sea level changes historically mirrored Volga runoff fluctuations, since 2006 the relationship has decoupled, suggesting additional climatic drivers beyond river inflow.To investigate these drivers, wind regime variability was analysed using Modern‑Era Retrospective analysis for Research and Applications, Version 2 (MERRA‑2) reanalysis data spanning 1980–2023. Statistical tests revealed no significant differences in average wind speed between the phase of sea level rise (1984–2004) and decline (2005–2022). However, the resultant wind speed increased by 10.3%, accompanied by a 9.5° shift in the predominant direction, indicating a reorganisation of atmospheric circulation over the basin. Comparison with the Southern Oscillation Index (SOI) and North Atlantic Oscillation (NAO) demonstrated moderate correlations, underscoring the role of global teleconnections in shaping evaporation and water balance dynamics.As a broader context, near‑surface air temperature across the Caspian region increased by ~1.3 ± 0.5 °C since the mid‑20th century, with ERA5 showing stronger warming in the north (~1.6 °C) and peaks up to 3.0 °C in Iran’s mountainous areas. This regional warming amplifies evaporation and interacts with wind regime changes, further accelerating sea level decline.These findings highlight that Caspian Sea level dynamics cannot be explained by river runoff alone, but are mediated through atmospheric circulation shifts and regional climate variability. By integrating hydrological records, wind regime analysis, and climate context, this study advances the scientific basis for forecasting and adaptation strategies. The results emphasise the need for coordinated climate‑hydrology assessments to anticipate future risks in the Caspian basin, where natural variability interacts with anthropogenic pressures.

1. Plastic waste has emerged as one of the defining environmental challenges confronting marine and coastal systems globally, with far-reaching consequences for ecological integrity, public health,...