The Shrinking Caspian Sea: Eco‐Hydrological Responses to Human and Climate Pressures

Authors

• Jesse Duku, University of California, Irvine
• Mohammad J. Tourian, University of Stuttgart
• Marzi Azarderakhsh, CUNY New York City College of TechnologyFollow
• Rovshan Abbasov, Khazar University
• Ali Mehran, San Jose State University
• Ali Torabi Haghighi, University of Oulu
• Stefanos Xenarios, Nazarbayev University
• Azara Boschee, University of California, Irvine
• Salih Babagiray, University of California, Irvine
• Mojtaba Sadegh, Boise State University
• Nima Shokri, Hamburg University of Technology
• Ali Nazemi, Concordia University, Montreal, Quebec, Canada
• Alireza Farahmand, California State University, Los Angeles
• Samaneh Ashraf, University of Montreal
• Temur Khujanazarov, Kyoto University
• Elmira Hassanzadeh, United Nations University Institute for Water, Environment and Health
• Dalal Najib, National Academies of Sciences, Engineering, and Medicine
• Daniel Placht, National Academies of Sciences, Engineering, and Medicine
• Shamshagul Mashtayeva, Al‐Farabi Kazakh National University
• Ekaterina Rets, Polish Academy of Sciences
• Hamid Norouzi, New York City College of TechnologyFollow
• Kaveh Madani, United Nations University Institute for Water, Environment and Health
• Manoochehr Shirzaei, United Nations University Institute for Water, Environment and Health
• Hossein Shafizadeh-Moghadam, Tarbiat Modares University
• Chiyuan Miao, Beijing Normal University
• Ali Mirchi, Oklahoma State University
• Shuo Wang, The Hong Kong Polytechnic University
• Amir AghaKouchak, University of California, Irvine

Document Type

Article

Publication Date

6-5-2026

Abstract

The Caspian Sea, the Earth's largest inland water body, faces water level decline, drawing comparisons to the collapse of the Aral Sea. Unlike the Aral Sea, the relative roles of climatic variability, hydrological changes, and anthropogenic pressures on the Caspian Sea remain poorly understood. Here, we integrate satellite observations, in situ hydrological records and reanalysis data to examine recent drivers of the Caspian water loss. We show that total river inflow to the Caspian Sea has declined significantly, primarily due to reduced discharge from the Volga River. At the same time, precipitation over the basin has remained broadly stable, while evaporation over the sea has shown a modest upward trend. These findings point to compound anthropogenic and climatic influences on the regional water balance. We also detect a long-term increase in chlorophyll-a concentrations in the shallow Northern Caspian, signaling growing ecological stress associated with ongoing hydrological change. Avoiding further ecological disruption requires coordinated international action and policies to mitigate shrinkage by optimizing water allocation and environmental releases, as well as prioritizing long-term ecosystem resilience. Without urgent intervention, the Caspian Sea risks following the trajectory of other desiccating inland water bodies, with long-lasting ecological and socioeconomic consequences.

Comments

This article was originally published in Earth's Future, available at https://doi.org/10.1029/2025EF008028

This work is distributed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). 

This project is funded by NSF Accelnet Award Number 2114701, managed by the National Academies of Sciences, Engineering, and Medicine.