The Caspian Sea is the largest closed body of water on the surface of the Earth. Its complete lack of any natural connection with the oceans makes it a very special ecosystem, and as such particularly vulnerable to external forces, such as climatic conditions or man-made changes to inflow.
The Caspian Sea has been endoreic – inwardly draining – since the Pliocene epoch (about 5 million years ago), prompting some specialists to treat it as the world’s largest lake. Studies of its geomorphology and hydrology have revealed alternating cycles of rising and falling water levels, raising many questions, scientific for some, more down-to-earth for those living on its shores.
| Figure: Most of the water flowing into the sea comes from coastal rivers – currently supplying 300 to 310 cubic km a year. The Volga alone accounts for 80% of inflow. But it has dropped substantially during the 20th century, declining from about 400 cubic km in the 1920-30s to between 260 cubic km and 270 cubic km at present, due to various climatic factors and human activities such as dams built for hydroelectric energy production. Rainfall over the sea itself is estimated to input 130 cubic km a year. Water loss through infiltration into the ground accounts for less than 5 cubic km and flow into the Kara Bogaz Gulf for about 18 cubic km, since the destruction of the dyke. Natural evaporation from the sea is estimated to produce a loss of between 350 cubic km and 375 cubic km a year. The combination of these water input (around 440 cubic km) and water loss (around 373 cubic km) estimates suggest that at present the water level in the Caspian Sea should be continuing to rise.
In a century, between 1880 and 1977, the level of the sea dropped four metres (from –25 metres to –29 metres below mean sea level) apart from short periods during which it rose slightly. During this time local people became accustomed to the gradual drop in the water level, carrying out all sorts of work on the shores, particularly after the second world war: port infrastructures, roads and railways, construction of housing and holiday facilities. In the Soviet Union the dramatic drying up of the Azov Sea, a side-basin of the Black Sea, which occurred at the same time, gave rise to genuine fears that the Caspian – or at least its very shallow northern part, which is less than 25 metres deep – would in turn shrink significantly. This led to hasty, misguided decisions such as the construction of a dyke in 1983 to close the Kara Bogaz Gulf.
The sudden reversal of the trend after 1977, with a rise in the water level of about two metres, took everyone by surprise and caused widespread problems in several areas: flooding of urban facilities, destruction of roads and railways, damage to industrial infrastructure on land and offshore, and destruction of beaches. Several tens of thousands of people in the lowlands of Azerbaijan, Daghestan and the Volga delta had to move. In Azerbaijan alone, damage resulting from the rise in sea level is estimated at $2bn. In Kazakhstan the encroaching sea has directly affected some 20,000 square kilometres of land, including the abandoned oil wells.
The factors behind the changes in the level of the Caspian are still the focus of debate. Scientists have not ruled out the involvement of tectonic (movement of the Earth’s crust below the sea) or geomorphologic causes (rate of sedimentation). However these would appear to have a minor impact in comparison to changing climatic factors, combined with the effects of human management of surface water in the Caspian basin. Most of the water flowing into the sea comes from coastal rivers. The quantity and quality of this water, particularly that of the Volga, are key variables in the balance of the Caspian. To this must be added rainfall over the sea itself. Water may be also be lost through infiltration into the ground and flow into the Kara Bogaz Gulf, but these factors are insignificant compared with natural evaporation from the sea.
The construction of a large number of dams and industrial facilities on the rivers feeding the Caspian has caused a significant change in the quantity of water inflow. The creation of a succession of large reservoirs, especially on the lower and middle Volga, has led to significant losses in flow rate due to additional evaporation from the surface of the water. Coupled with unsustainable water consumption, in particular in connection with irrigation, the river flow rate is now only 10 % of the natural levels.
Uncertainty regarding future variations in the sea level is holding back the development of many coastal zones suitable for holiday amenities or the construction of ports. It also complicates further offshore oil prospecting, currently expanding in the north-east corner of the sea, off the coasts of Kazakhstan and Russia. The very shallow water in this part poses problems of access and safety.
The Caspian Sea region is climatically diverse encompassing the basins of the Volga and Ural rivers in the North, the vast semi-arid and hot arid plains of northern Kazakhstan and Turkmenistan in the east, and the humid Caucasus and Elburz mountains in the south-west. The Caspian Sea plays an important role in atmospheric processes, regional water balance and microclimate.
Climatic phenomena in the Caspian are linked to the Northern Atlantic Oscillation (fluctuations in atmospheric air pressure). These variations affect temperatures, moisture and winter storms all across Europe including the Volga basin, as well as rainfall over the Caspian basin.
Several severe droughts have affected various parts of the region in recent years. They seem to confirm scientific models, which, in addition to higher mean temperatures, generally predict more extreme weather events. Droughts affect both crop production and the health of livestock. For example, the economically important Karakul sheep of Turkmenistan, which are raised for wool production, are sensitive to heat stress. In addition to the loss of agricultural productivity, droughts can increase the frequency and severity of fires, which may destroy grassland and crops.
Contrasting rainfall trends have been observed in the north and south. Whereas rainfall over Russia has increased over the last century, already dry areas such as the coasts of Turkmenistan and Iran have become even drier. Dust storms pick up large amounts of salt and dust as they pass over the Kara-Kum desert and the Caspian shore, depositing it in the Volga valley where it impairs the fertility of arable land.
But the availability of freshwater, on which many sectors of the economy – and human well-being – depend, is also linked to more remote climatic processes. If glaciers in the Caucasus and Elburz mountains recede and the periods of snow cover become shorter, as has been the case in recent years, less water will be available for use in irrigation and homes.
Melting glaciers do not only result in the disappearance of pretty white mountain caps. The processes caused by warmer mean temperatures also increase the risk of natural disasters associated with changing environmental conditions. For example, in the last 30 years mudflows in the Terek river basin in the north-eastern Caucasus have occurred almost annually. The most destructive mudflows were recorded in 2000 and were perhaps linked to persistent above-average summer temperatures. In September 2002 the Kolka glacier near Mount Kazbek, the highest peak in the eastern Caucasus, collapsed. The water that had accumulated inside and below the glacier triggered an avalanche that travelled more than 24 kilometres at very high speed killing over 120 people.
Human activities can have a powerful influence on the local climate. Widespread irrigation networks and dams are depleting the soil, exposing it to erosion. Ground water supplies are thereby reduced, which can cause the whole water regime to change. This can influence local temperatures and consequently the evaporation potential.
Oil and gas exploration activities not only cause localised pollution of air, soil and sea, but also emissions of greenhouse gases such as methane (CH4) and carbon dioxide (CO2) that add to the global greenhouse effect and lead to warming of the atmosphere. It is estimated that on and off-shore fossil fuel production in the Caspian area emits 15 to 20 million tonnes of CO2-equivalent annually. The expected rise in fuel production will further increase greenhouse gas emissions unless appropriate counter-measures are taken.
It is difficult to predict how climatic changes at the global level will affect the climate of a particular region. Although climate scenarios commonly suggest warming and increased rainfall over the north of the Caspian and its vicinity, with lower rainfall to the south, there is considerable uncertainty as to the influence of the sea, the effects of the complex topography, cloud cover, and other factors.
The critical point is that there is no way of predicting whether the climate system will react in a linear way or if it will suddenly collapse in one way or another once a critical threshold is reached. As the concentration of greenhouse gases in the atmosphere increases, the temperature in the European part of the Caspian Sea region will continue to rise, at least at first. Some researchers have recently expressed fears that the warm Gulf Stream current in the Atlantic Ocean may slow down due to the changes in the Artic environment and oceanic circulation. As a result, the regional temperatures could drop significantly creating an extremely harsh climate.