The Caspian Sea is the biggest inland body of water in the world. Its surface area is roughly equivalent to the combined area of the Netherlands and Germany (about 400,000 km2, or 144,000 mi2). The surface water inflow into the sea is formed by the flow of the Volga, Ural, Terek, Sulak, Samur, Kura, small Caucasian rivers, and Iranian rivers. The watershed area of the Caspian Sea is 3.5 million square kilometers. The basin of the Volga River makes up nearly 40% of the territory of the catchment of the Caspian Sea, and it supplies about 80% of the total volume of annual water flow into the sea. All components of the Caspian ecosystem, directly or indirectly, to a greater or lesser extent, are influenced by river flow.

The Caspian Sea basin falls into three morphologically different parts: (I) the northern (25% of the sea area), a shallow area (less than 10m deep; about 20% with depths less than 1 m) extending to a conventional line passing from the Terek river to the Mangyshlak Peninsula; (If) the medium (35%), with an average depth of 170 m (the maximum being 790 m); and (iff) the southern (39%), the deepest area, with a maximum depth of 1025 m and an average depth of 325 m (see Fig. 1). Deep depressions in the northern and southern parts of the sea are divided by an underwater threshold running from the Apsheron Peninsula to Turkmenbashi (formerly Krasnovodsk) (Kosarev and Yablonskaya, 1994).

Before the breakup of the Soviet Union in December 1991, the USSR and Iran were the only two independent nations occupying the shores of the Caspian. With the breakup, three additional newly independent nations emerged along the coast: Azerbaijan, Kazakstan, and Turkmenistan. The Russian Federation's Caspian coastline is shared by three of its political units: Astrakhan Oblast, the Republic of Kalmykia, and the Republic of Dagestan.

Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts, Edited by Thomas D. Potter and Bradley R. Colman. ISBN 0-471-21489-2 © 2003 John Wiley & Sons, Inc.

Figure 1 Depth isolines for the Caspian Sea, in meters.

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