Caspian Sea: State of the Environment 2019

than the average for the 1961–1990 period. In general, the water temperature in the Makhachka- la area of the Caspian Sea has been rising 0.06°C per year for the last 30 years. Time series data re- veal anomalies in the water temperature that differ to those for air temperature: during 1997–2007, only positive water temperature anomalies were observed, while in the years before and after this period, positive anomalies alternated with nega- tive anomalies (CASPCOM 2017). According to the CASPCOM assessment (2017), which not only covers water temperature chang- es, but also the variability of surface water run-off into the sea, in the last quarter of the twentieth century, the Caspian Sea was impacted by glob- al warming, with the air temperature over the water increasing by 0.7–0.8°C and the surface water layer by 0.4–0.5°C. At first, the warming occurred alongside a rapid rise in sea level, fol- lowing increased flow from the Volga and Ural Rivers into the Caspian Sea, despite a decreased flow from the Kura River. At the turn of the cen- tury, the levels of run-off decreased, causing sea levels to slowly decline. Since 2006, the Caspian Sea level has been declining rapidly and global warming has slowed down, with run-off normal- izing and sea level stabilizing in 2016–2017.

3.3.2. Impact and contribution to climate change

The Caspian Sea’s water column, with the ex- ception of its freshwater inflows in the Northern Caspian, has relatively uniform salinity. Since the salinity is fairly evenly distributed, impacts on water mixing, the level of biogenic elements present in the photic zone and the water’s bio- productivity are largely the result of climate change. Climatic factors that stimulate deep water mixing in the Caspian Sea are diverse. Re- gional atmospheric circulation creates vortices, causes declines and rises in water levels and also increases the density of the water’s surface layer, resulting in summer evaporation, winter cooling and ice cover formation. Salinity fluctuations in the water’s surface layer also influence deep mix- ing, due to changes in the volume of river inflows and atmospheric precipitation. The Northern Caspian is the smallest section of the Caspian Sea in terms of both volume (0.5 per cent) and area (33.8 per cent), with an average depth of 4.4 metres, making it more susceptible to any changes in the atmosphere above its wa- ters. Fluctuations in run-off from the Volga River also affect the Northern Caspian, where the flow

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