Caspian Sea: State of the Environment 2019

are Kura, Samur, Gudyalchay, Valvalachay and Lankaranchay. The Kura River’s watershed area is 188,000 km 2 and the annual run-off is 18.0 km 3 (Imanov 2016). Two major rivers flow into the Caspian Sea from Iran: the Sefid-Rud River and the Gorgan Riv- er. The Sefid-Rud River’s catchment area is about 56,200 km² and the average long-term run-off is 4.1 km³. Run-off from the Gorgan River is used for irrigation and therefore does not have a permanent flow into the sea (Jalalvand and Gaidukova 2017). The Ural River, which flows through Kazakh- stan and the Russian Federation, is 2,428 km and drains an area of 237,000 km 2 . It is the third-lon- gest river in Europe after the Volga and the Dan- ube. The average water discharge at the mouth of the river is 400 m 3 /second (Chibilev 1987). The Emba River in west Kazakhstan rises in the Mugodzhar Hills and flows 720 km, though its waters only reach the Caspian Sea when water is abundant. The river has a watershed area of around 40,400 km 2 (Zonn et al. 2010).

From Russia, the following rivers flow into the Caspian Sea: Volga, Terek, Sulak and Samur (which is the border river with Azerbaijan). The average long-term run-off of the Volga River is 255 km 3 or about 80 per cent of surface run- off into the sea (Monakhov 2014a; Monakhov 2014b; Monakhov 2015). One river stems from Turkmenistan: the Atrek River. Like the Gorgan River in Iran, run-off from the Atrek River is used for irrigation and therefore does not have a permanent flow into the Caspian Sea (Shults 1965). The Caspian Sea is a brackish water body, with an average salinity of 12.7 grams per litre, though it ranges from 12.6 to 13.2 grams per litre. In the northern part, the range varies more greatly from 1 to 8 grams per litre. The water temperature on the sea surface in summer reaches 24–27°C and in winter ranges from 0°C in the north to 11°C in the south. In summer, hypoxia occurs in the bottom layer of the north-western part of the sea (Zonn et al. 2010).

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