Stefanos Xenarios, Serik Orazgaliyev, Ali Torabi Haghighi & Bjorn Kløve
To cite this article: Stefanos Xenarios, Serik Orazgaliyev, Ali Torabi Haghighi & Bjorn Kløve (2025) A perspective on sustainability and environmental challenges in the Caspian Sea, International Journal of Water Resources Development, 41:1, 1-8, DOI: 10.1080/07900627.2025.2441052
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INTERNATIONAL JOURNAL OF WATER RESOURCES DEVELOPMENT 2025, VOL. 41, NO. 1, 1–8 https://doi.org/10.1080/07900627.2025.2441052
EDITORIAL
A perspective on sustainability and environmental challenges in the Caspian Sea
The Caspian Sea, the world’s largest salt lake, has a complex geological and hydrological history spanning millions of years. Originally connected to the world ocean via the Black Sea and the Mediterranean Sea until about 6 million years ago, it became an enclosed body of water during the Late Miocene period (Zubakov, 2001). This isolation has resulted in a fascinating evolutionary history by creating a unique interaction between continental and maritime conditions. The shores feature diverse biomes, ranging from cold continen- tal deserts in the north and east to warm highlands in the south and southwest. The Caspian Sea is also abundantly endowed with petroleum and natural gas reserves, which, in conjunction with its valuable fisheries, render it a central focus for both regional and global economic and political interests (Xenarios & Neafie, 2022). Its strategic location at the crossroads of Europe and Asia further enhances its significance in international affairs.
This Special Issue seeks to identify the sustainability and environmental challenges in the Caspian Sea, as well as the initiatives and policies necessary for promoting sustainable water management within national and regional frameworks. In this Editorial, we initially deline- ate the geophysical, historical and geopolitical contexts in the Caspian Sea by further addressing the climatic, hydrological, environmental and socioeconomic challenges pre- sented in this issue and outlining the initiatives for a sustainable future in the region.
With a surface area of 390,000 square kilometres and an estimated water volume of 78,700 cubic kilometres, the Caspian Sea is fed by a diverse network of rivers, including 130 rivers of various sizes, contributing an annual inflow of approximately 300 cubic kilometres. The Volga River alone accounts for 80% of this input, with additional con- tributions from the Ural, Terek, Sulak, Samur and Kura rivers and smaller rivers in Iran and the Caucasus (Chen et al., 2017). These rivers form the lifeline of the Caspian’s hydrology, while the closed nature of the basin amplifies the sensitivity of the water balance to climatic and anthropogenic factors (Sharifi et al., 2024).
With a mean depth of approximately 230 metres and a surface water level about 28 metres below mean sea level, the Caspian Sea has experienced significant fluctuations in surface water level and surface area since 1940. These changes have occurred at a rate 100 times faster than the global sea level changes observed over the past century (Akbari et al., 2020). The area of the Caspian Sea is divided into three approximately equal parts with dramatically different volumes, depths and salinity: Northern, Middle and Southern. The Northern Caspian is the shallowest, with an average depth of around 6 m, and about 29% of the entire sea area, though its volume is less than 1%. The salinity in the Northern parts ranges from 0.1‰ near river mouths to 10–11‰ as the water flows into the middle basin (Zonn et al., 2010). The Middle and Southern Caspian parts comprise about 35% of the sea each, with considerably higher volumes of about 35% and 64% and depths ranging from 190 m in the Middle to more than 1000 metres in the South (Aladin & Plotnikov, 2004). The salinity levels in these parts of the sea
are more stable, ranging between 12.6% and 13.5%, with slight increases proportional to the depth in eastward regions (Bezrodnykh et al., 2020). Such variation in salinity, combined with seasonal and long-term changes in water levels, has profound implications for biodiversity, particularly in the Caspian’s large shallow areas, which serve as critical habitats for numerous endemic species.
The climate of the Caspian region reflects the confluence of several Köppen climatic zones: Arctic air masses, moist Atlantic winds, dry continental air from Kazakhstan and warm air currents from the Mediterranean and Iran (Koriche et al., 2021). This interaction of climatic systems results in significant seasonal variability, including freezing temperatures in the north- ern regions during winter, where ice formation plays a crucial ecological role. The Caspian Sea’s ecological richness makes it one of the world’s most valuable ecosystems largely due to its prolonged isolation from other water bodies, resulting in the development of a unique brackish-water fauna (Esin et al., 2018). The Caspian today supports an extraordinary diversity of habitats, including vast river deltas, extensive wetlands and dynamic coastal ecosystems. The high rate of biological endemism is exemplified by species like sturgeon, which account for 85% of the global sturgeon population, forming the backbone of the region’s lucrative caviar industry (Bodini et al., 2024). Moreover, the Caspian lies at a crucial crossroads for millions of migratory birds and provides refuge for numerous rare and endangered species, further emphasizing its global ecological significance (Byholm et al., 2022).
The socioeconomic history of the Caspian Sea region before the Soviet Union was characterized by periods of trade expansion, geopolitical shifts and resource exploitation. In the 16th century, the Caspian Sea became a geopolitical extension of the Volga River system following Russian conquests, leading to increased Russo-Persian trade. This devel- opment opened new trade routes to Europe, bypassing Ottoman-controlled areas. The 16th century also saw increased piracy and marauding along the Caspian coast, threaten- ing coastal communities (Mahdavi, 2013). By the early 19th century, two significant conflicts known as the Russian-Persian wars (1804–1813 and 1826–1828) ultimately resulted in an increased Russian presence and authority in the area, particularly through maritime trade. The number of steamships on the Caspian Sea rose in the latter half of the 19th century, supporting rapid growth and trade (Bayramov, 2021).
In the early days of the Soviet Union, the 1921 Treaty of Friendship between the USSR and Persia established the basis for bilateral relations, including navigation rights. The 1935 and 1940 treaties between Iran and the Soviet Union further defined the legal regime of the Caspian Sea, reserving navigation and fishing rights exclusively for Soviet and Iranian vessels. The mid-20th century saw the beginning of oil and gas exploitation in the Caspian basin, which would later become a significant economic factor for the region (Effimoff, 2000). The Soviet Union began offshore drilling in the 1940s, followed by Iran in the 1950s. Throughout this period, the Caspian Sea experienced water-level fluctuations, which impacted economic activities such as fishing and shipping. These changes also influenced settlement patterns and land use along the coastlines. The socioeconomic history of the Caspian Sea until 1991 was characterized by the gradual development of fishing industries, the emergence of petroleum exploitation, and the establishment of legal frameworks governing the sea’s resources and navigation rights between the primary stakeholders, Iran and the Soviet Union.
The dissolution of the Soviet Union in 1991 dramatically altered the political landscape by increasing the number of riparian states from two to five, comprising Azerbaijan to the
INTERNATIONAL JOURNAL OF WATER RESOURCES DEVELOPMENT 3
southwest, Iran to the south, Kazakhstan to the northeast, Russia to the northwest and Turkmenistan to the southeast. The emergence of Azerbaijan, Kazakhstan and Turkmenistan as independent states necessitated a redefinition of maritime boundaries among the Caspian littoral countries. The Caspian region after 1991 entered a new phase characterized by resource-driven development, marking the beginning of what is frequently referred to as the ‘second Caspian oil boom’ (Bayramov & Abbas, 2017). This period has positioned the region as a pivotal centre in global geopolitics, primarily due to its extensive hydrocarbon resources. The abundance of these resources has attracted significant interest from external powers, resulting in heightened geopolitical competition, which remains evident to this day. The United States (US) has established a significant presence in the region by successfully acquiring key contracts from major American oil companies with states in the Caspian area, often outmanoeuvring their international competitors. In response to this development, Russia has endeavoured to counterbalance the influence of the US, particularly concerning negotiations related to the construction and routing of oil pipelines. Simultaneously, countries within the European Union have pursued both strategic and commercial objectives in the region, with their oil companies actively engaged in various initiatives and projects.
The Caspian basin’s resource wealth underscores its potential to contribute sig- nificantly to the global energy market. According to estimates by the US Energy Information Administration (EIA), the region holds approximately 50 billion barrels of oil and 292 trillion cubic feet of natural gas, which are still unexplored all over the territory (US EIA, 2013). Moreover, the actual reserves are believed to be higher, fuelling the aspirations of littoral states to emerge as leading global energy suppli- ers. For example, Turkmenistan claims to possess the world’s fourth-largest natural gas reserves, while Kazakhstan has articulated its ambition to rank among the top ten global oil producers. However, the development of many oil and gas deposits remains constrained due to disputes over jurisdiction and overlapping territorial claims.
The legal status of the Caspian Sea has been contentious, with persistent disagreements concerning demarcation and resource exploitation over the past two decades. This dispute was particularly critical given the significant oil and gas reserves located within the seabed, as many major projects, including pipeline infrastructure, depend on resolving these legal ambiguities. Moreover, the uneven distribution of hydrocarbon resources along the Caspian coastline has further complicated efforts to reach a consensus, making this issue a persistent challenge for all littoral states. A critical point in the prolonged dispute among the littoral states of the Caspian Sea has been classifying this body of water as either a ‘sea’ or a ‘lake’. This distinction has significant implications, as it determines the applicable interna- tional legal frameworks governing ownership rights over the water and its resources. If classified as a ‘lake’, customary international law would prevail, requiring unanimous agree- ment among the littoral states for any resource exploitation. From the outset, Iran and Russia have supported the ‘lake’ designation, perceiving it as more advantageous to their interests. In contrast, Azerbaijan and Kazakhstan, which possess substantial hydrocarbon reserves along their coastlines, have argued for the designation of the Caspian as a ‘sea’. Such a classification would allow for the application of the 1982 United Nations Convention on the Law of the Sea (UNCLOS), facilitating the division of the Caspian into national sectors and granting each state exclusive rights to resources within its designated area (Orazgaliyev, 2018). This disagreement hindered the development of a comprehensive legal regime for nearly three decades.
4 EDITORIAL
Following extensive negotiations and diplomatic engagements, the Convention on the Legal Status of the Caspian Sea was officially signed in Aktau, Kazakhstan, in August 2018. The five participating countries consented to collaboratively manage the Caspian Sea’s natural resources by integrating principles of international maritime law alongside those applicable to endorheic lakes. The agreement established a framework for dividing the Caspian’s resources by granting to each country fifteen nautical miles of territorial waters and an additional ten nautical miles of fishing rights and designated the surface waters beyond these zones for common use. The agreement also foresaw underwater pipelines to be laid with the consent of only the countries whose sectors they pass through. The military presence in the region was also regulated by prohibiting the presence of military forces from non-littoral states in the Caspian Sea. Despite this breakthrough, unresolved issues remain. Bilateral agreements on maritime borders between some states are still pending, and mechanisms for dividing and managing the Caspian’s hydrocarbon resources continue to be a critical area of negotiation (Orazgaliyev & Araral, 2019). Also, environmental condi- tions are expected to deteriorate, mainly due to oil and gas malpractices, which consider- ably impact terrestrial and aquatic habitats and ecosystem services.
Intergovernmental agreements have been established for the sustainable manage- ment of the Caspian Sea, including the Framework Convention for the Protection of the Marine Environment, signed in Tehran on 4 November 2003 (commonly referred to as the Tehran Convention). Nonetheless, the ecosystems of the Caspian Sea are increasingly subjected to pressures from both natural phenomena and anthropogenic activities. Climate change has added a new layer of complexity to the Caspian’s challenges. A comprehensive analysis conducted by Naurozbayeva et al. (2023, in this issue), has significantly enhanced the understanding of the intricate relationships among climate change, atmospheric circulation, and the ice regime of the Caspian Sea, highlighting their implications for the region’s ecosystem. The research underscores the critical role of ice cover concerning navigation, the infrastructure of offshore oil platforms and its profound impact on the breeding habitats of the endangered Caspian seal population. In another research conducted by Hoseini et al. (2024, in this issue), which utilized 13 global climate models across four shared socioeconomic pathways scenarios, future projections suggest an increase in temperatures over the Caspian Sea in the 21st century, ranging from 0.4 °C to 3 °C. These climatic changes present significant environmental challenges for the region, affecting ecosystems, coastal wetlands, biodiversity and water resources. Also, Moradian et al. (2024, in this issue), indicate how extreme precipitation events pose risks of flooding and drought and aggravate water resources management and planning in the region. Rising temperatures and shifting precipitation patterns are accelerating evapora- tion rates and altering the delicate water balance of the sea, leading to increasingly unpredictable water levels.
Climate variability also has a significant impact on the phenological patterns of vulnerable coastal ecosystems in the region. According to Ghadimi et al. (2024, in this issue), the Hyrcanian forests located in the southern coastal zone of the Caspian Sea are experiencing rising trends in mean annual temperature. The temperature increase is expected to lead to greater evapotranspiration and subsequent soil moisture defi- cits. These changes are likely to adversely affect critical ecosystem services and the habitats of various wildlife in the southern coastal zone of the Caspian. Transformations of a similar nature are evident within aquatic ecosystems. As noted
INTERNATIONAL JOURNAL OF WATER RESOURCES DEVELOPMENT 5
by Fendereski (2023, in this issue), alterations in water temperature and quality substantially disrupt the phenology of primary producers, including phytoplankton. The study’s findings indicate substantial ecoregion-scale variations in algal blooms’ timing, duration, magnitude and interannual variability, particularly in the northeast- ern and southern ecoregions. These variations suggest a heightened sensitivity of these regions to recent environmental changes.
Environmental changes have also adversely affected biological processes, resulting in a decline in the productivity of commercially significant fish species. The appearance of invasive species, such as the comb jellyfish Mnemiopsis leidyi, has further disrupted food webs and intensified ecosystem stress (Roohi et al., 2024). Fluctuations in sea levels due to the regulation of rivers present additional challenges, as the rising and falling waters alternately inundate or expose critical habitats. This phenomenon is particularly pro- nounced in the Northern Caspian, which exhibits significantly higher productivity than the Middle and Southern Caspian regions (Aladin & Plotnikov, 2004). Furthermore, habitat loss attributable to river regulation has led to a marked reduction in delta vegetation, degrading essential spawning grounds and nesting sites. Also, the effects of environ- mental changes on aquatic species, are profound in the iconic sturgeon of the Caspian Sea. The Caspian Sea is home to the world’s largest caviar-exporting industry, accounting for over 80% of the global supply. Overfishing and illicit fishing activities, particularly targeting sturgeon, have resulted in significant population declines, jeopardizing the survival of this economically and ecologically valuable species. A study by Berman (2024, in this issue) presented a detailed review of Soviet-era and contemporary aqua- culture practices. Berman’s research highlights the various factors contributing to the conservation risks facing sturgeon in the Caspian Sea. The study underscores the necessity of supporting market-oriented approaches with comprehensive research initiatives to preserve the environments and habitats essential for sturgeon species.
The growing exploitation of oil and gas resources and the expansion of maritime transportation, which positions the Caspian as a strategic corridor between Europe and Asia, have provided major development opportunities for the littoral states, albeit with increased environmental risks. In this context, Neafie et al. (2024, in this issue), have developed a hybrid environmental sensitivity index (ESI) designed to assess both the socioeconomic and ecological vulnerabilities to oil spills along the shorelines of Azerbaijan. The study advocates for enhancing the ESI and similar initiatives through improved monitoring and data collection, fostering community engagement to bolster local resilience, and implementing oil spill management and preparedness plans. These measures should be supported through collaborative partnerships between the public sector, private industry and government agencies. The environmental risks associated with oil spills have also been emphasized by Pentayev et al. (2024, in this issue), who proposed a multi-modal methodology for detecting oil spills in the Caspian Sea. This methodology integrates remote sensing, deep learning and natural language processing techniques. The study underscores the urgency of improving oil spill detection in the Caspian Sea to avert irreversible environmental damage and significant economic losses. The proposed approach is anticipated to facilitate early and precise detection of oil spills, informing timely response actions. Furthermore, it is expected to be instrumental in developing more effective environmental regulations, particularly in regions lacking adequate mon- itoring systems.
6 EDITORIAL
The necessity for environmental improvement within the region is also addressed by Nurmatov et al. (2024, in this issue) who underline the economic potential in the Caspian Sea’s tourism sector, particularly for Kazakhstan, Russia and Azerbaijan. The study high- lights the adverse effects of the COVID-19 pandemic and the ongoing Ukrainian-Russian conflict on tourism-related activities in the Caspian region. However, the authors assert the robust growth potential of the tourism sector in the Caspian region upon improved planning and coordinated regional initiatives.
The Caspian region has become increasingly important in 21st-century geopolitics, particularly due to its vast hydrocarbon resources. This has attracted interest from global powers, leading to what some describe as a new ‘Great Game’ in Central Asia (Blank, 2012). However, hydrocarbon-dependent economic growth comes at the expense of major environmental pollution threats, which, together with the decreased freshwater from heavily regulated rivers in the north Caspian, uncontrolled and illicit sturgeon and other species fishery and loss of habitats due to global environmental changes, have put at risk critical ecosystem functions and services in the wider region.
The Caspian Sea constitutes an invaluable natural resource, serving as a vital asset not only for the regional stakeholders but also for the global community. Its ecosystems support an extraordinary diversity of life and provide critical services, from fisheries to carbon sequestra- tion. However, without sustainable management, the cumulative impacts of human activity and climate change could irreparably damage this unique environment. The Caspian Sea’s water governance faces a critical gap between scientific knowledge and policymaking, undermining the translation of research into actionable solutions (Bamal et al., 2023).
Establishing a unified governance framework, fostering collaboration among coastal states and aligning efforts with international principles are essential to safeguard the region’s environmental and human security for future generations. This special issue combines essential research to inform solutions, offering insights into the challenges and opportunities for preserving the Caspian’s ecological and socioeconomic value. As the largest enclosed sea on the planet, its future is contingent upon our collective capacity to reconcile development with conservation efforts. This balance is essential to preserve its rich biodiversity and resources for the benefit of future generations.
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8 EDITORIAL
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Stefanos Xenarios
CSIRO Environment, Canberra, Australia Graduate School of Public Policy, Nazarbayev University, Astana, Kazakhstan SDSN Kazakhstan, Nazarbayev University, Astana, Kazakhstan stefanos.xenarios@csiro.au http://orcid.org/0000-0002-5564-5661
Serik Orazgaliyev
Graduate School of Public Policy, Nazarbayev University, Astana, Kazakhstan SDSN Kazakhstan, Nazarbayev University, Astana, Kazakhstanhttp://orcid.org/0000-0002-8273-7633
Ali Torabi Haghighi
Department Water, Energy and Environmental Engineering, Faculty of Technology, University of Oulu, Oulu, Finland http://orcid.org/0000-0002-5157-0156
Bjorn Kløve
Department Water, Energy and Environmental Engineering, Faculty of Technology, University of Oulu, Oulu, Finland http://orcid.org/0000-0002-2353-1440