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Water Balance

The considerable degree of isolation from the World Ocean, the big draining masses and great number of flowing rivers contribute to the unique water balance of the Black Sea. The water balance is an important factor in the Black Sea ecosystem. The changes in the salt and water balance, which are very vulnerable to all kinds of anthropological changes, especially concerning the surface, the bioproductiv northwest region. The flowing freshwater and the exchange Bosphorus are critical elements in the hydrography and the ecosystem of the Black Sea. The water balance has been studied for many years and there are a lot of arguments about its sizes.

River flowing

The biggest mass of river flows in the Black Sea comes from the northwest part of the basin and from Caucasus, the Turkish, Bulgarian and Romanian coasts. The whole surface of the flowing rivers is 1 874 904 square km, including 215 625 square km of small river flows. The average total flow from 1921 till 1988 was 353 square km every year.

Flowing rivers from the northwest coast

The total area of the northwestern coast rivers is about 1 500 000 square km , including also 20 000 square km of small river flows. Many of the flowing masses come from four main rivers - the Danube, the Dniester, the Dnieper and the South Bay. The average annual flow in the northwestern parts for the period 1921-1988 was 261 cubic km per year, increasing to 153 cubic km in 1921 and 389 cubic km in 1970. 

Flowing rivers from Crimea

The rivers from Crimea don"t have important influence on the Black Sea balance. The biggest rivers are the Chernaia, the Belbek, the Alma and the Kacha. The total area of all rivers, coming from the Crimean mountains into the Black Sea is only for the period 1921-1988 was 0,32 cubic km, including the minimum of 0,07 cubic km in 1930 and the maximum of 0,67 cubic km in 1968.

Flowing rivers from Caucasus

The total area of all rivers, coming from Caucasus is about 75 000 square km. More important rivers are: the Riony, the Ingury, the Kodory, the Bzib, the Supsa and the Mzimta. The average annual flow is 43 cubic km, varying from 31 cubic km in 1969 to 57 cubic km in 1922.

Flowing rivers from Turkey

A lot of rivers flow into the Black Sea from the Turkish coast. Their total area is 295 550 square km. The main rivers are: the Iesilirmak, the Kizilirmak amd Sakaria. The average annual flow for the period 1930-1986 is 36 cubic km, varying from the minimum of 25 cubic km in 1949 to the maximum of 51 cubic km in 1940. 

Flowing from Bulgarian and Romanian coast

The main rivers in Bulgarian are: the Kamchia, the Provadijska, the Rezovska, the Veleka, the Ropotamo and the Fakijska. Their total area is 6, 292 square km . The total flow varies about 1,83 cubic km per year. The total area of all rivers, coming from the Romanian coast is 4, 589 square km. Their average annual flow is 0,12 cubic km.

Precipitation

The precipitation in the Black Sea is caused by the cyclone activity. The cyclones move mainly from the west to the east, through the southern part of the sea. The eastern and the southern region have more intensive precipitation. The least intensive precipitation is in the central and especially in the west part. The monthly precipitation (above the sea) reaches the maximum in winter (40‰) and the minimum in spring and the beginning of the summer (15‰). There are sometimes summer sediments on the coast, especially in the northwest zone, caused by the heat convection (carring). The average precipitation on the total Black Sea bottom area is 225 cubic km per year. The total precipitation is nearly 1.5 times less than the total river flow, but its influence over the total precipitation varies significantly in different years and seasons. For example in autumn and winter the quantity of precipitation on the bottom increases the continental flowing masses.

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