Location and Morphometry
The Caspian Sea locates in the southern-eastern part of Europe just at the Europe-Asian border having the coordinates 30-47oN and 46.5-55oE. Its elevation is approx. -28 m below sea level. The sea is endorheic basic elongated in north-southern direction. The Caspian sea is surrounded by the Caucasus Mountains from the west, the Reshteh-ye Alborz Mountains from the south, the Prikaspiyskaya Nizmenost' (Caspian Lowland) from the north and the Ustyurt Plateau and the Turan Lowland from the east. From the western winds and Mediterranean cyclones the Caspian Sea is strongly protected by the Caucasus Mountains.
Morphometrical characteristic of the Caspian Sea are as following: the lake surface area - 378,400 km2, lake basin volume - 78,170 km3 (approx. 40% of the world's continental surface water), average and maximum lake depth - 210 and 1025 m, shoreline length - 6000 km, lake maximum length and breadth - 1180 and 480 km, shoreline development - 2.75 and volume development (a ratio of average to maximum depth) - 0.21. In comparison with other greatest natural lakes of the world (see figure on the right: comparison of surface areas), the Caspian Sea ranks first in surface area and lake volume, and both the 3-d in average and maximum depths (after Lakes Baikal and Tanganyika). Two deep (max depth 1025 and 788 m) and one shallow (max depth 20 m) basin occupy its southern, central and northern parts respectively. These facts lead to horizontal differences in temperature, salinity, hydrological and hydrobiological regimes. Nutrient levels and primary production of the sea are low. Historically, the Caspian Sea level has fluctuated by -6 m, but on the geological timescale, fluctuations of >200 m have occurred.
Geological History and Origin
It is widely accepted in limnology the Caspian Sea is of tectonic uplift origin. However, its history falls in two parts: i) a Miocene stage, determined by tectonic events associated with the closing of the Tethys Sea, and ii) a Pleistocene stage, determined by glaciation cycles and the genesis of the modern Volga River.
General climatic conditions
Climatic characteristics above aquatory of Caspian Sea and its shoreline are combined under influence, first of all, of global atmospheric processes, local air circulation and deforming influence of enclosing landscapes, main of which are Caucasus mountains, Elbrus, Kopet Dagh, deserts of Central Asia etc.
In different seasons of year the weather conditions are influenced by intrusion of air masses, formed above Northern Ice Ocean, Northern Atlantic, Mediterranean sea, Western Siberia, that bring to aquatory moistures as rainfalls and cloudiness, or other aerosol inclusions, and the salt from mechanical evaporation above water surface. By such way forms regime of cloudiness inherent to these area, temperatures and humidity of air, a direction and speed of winds, a component of radiating balance, waviness, current, temperature of water, a transparency of water and air etc.
Caspian Sea renders the certain influence on atmospheric processes and a climate of environmental land. In annual balance the sea provides some warming effect that shown more often on southern and northern parts of the sea and around Absheron peninsula. In the middle side its warming influence in the winter is replaced by cooling influence in the summer season.
For more climate information of the Caspian Sea please check the special climate section.
Other characteristics
The Caspian Sea is special in numberous ways. The change in salinity from north to south and the watertransparency are just two of those. Please check the sea-characteristics pages for more detailed information about the seawater.
General Features of Watershed
The Caspian Sea watershed (catchment) area occupies the vast European and Asian territory between approx. 33o-58oN latitude and 30o-62oE longitude. In comparison with other world great natural lakes, the Caspian Sea ranks first in watershed area (3660,000 km2) and also in a total annual rivers runoff (340 km3/year - long-term average value). The above figures give long-term average specific discharge from the entire watershed into the sea equal to approx. 3.0 l/s×km2. Since the Caspian Sea, similarly as almost all saline and brackish world lakes, is a closed lake (without surface outflow), total rivers inflow is the main income part of its water balance. It should be noticed, however, that both specific watershed (watershed to lake surface area ratio) and retention (residence) time (lake volume to total annual rivers runoff ratio) of the Caspian Sea equal 9.7 and approx. 230 years, respectively, are not the biggest ones in the world.
Nations, Cities and Administrative Units within the Watershed
The Caspian Sea watershed covers vast territory including Azerbaijan, parts of Turkmenistan (Balkansk oblast), eastern Georgia, northern Iran, western Kazakhstan (Zapadno-Kazakhstan, Gur'yev, Aktyubinsk and Mangistausk oblasts), central-western and southern regions of Russia. The Russian part mainly includes administrative unites surrounding the rivers inflowing the Caspian Sea: River Volga (Kalmik, Boshkortostan, Chuvash, Udmurt, Mary-El and Tatarstan Republics, Astrakhanskaya, Saratovskaya, Samarskaya, Volgogradskaya, Nizhegorodskaya, Yaroslavlskaya, Moscowskaya, Tverskaya, Kostromskaya, Ivanovskaya and Ulyanovskaya oblasts), River Terek (Chechnya-Ichkeria, Dagestan, Osetiya-Alania and Kabardino-Balkar Republics), River Kuma (Kalmik Republik, Stavropolskii Kray), River Ural (Bashkirtastan Republik, Orenburgskaya and Chelyabinskaya oblasts) and some others.
Total population of Russian part of the Caspian Sea watershed reaches 50 millions. According to (The Times Atlas... 1999) modern population of Kazakhstan, Turkmenistan and Iran reaches 16.6, 4.1 and 67.3 millions respectively. However, there are no correct data on population of Kazakh, Iranian and Turkmen parts of the Caspian Sea watershed. Nevertheless, the total population of the Caspian Sea watershed including Azerbaijan, parts of Georgia, Iran, Kazakhstan, Russia and Turkmenistan could be roughly estimated as >70-80 millions.
Climatic features of the watershed
The elevation of the Caspian Sea watershed varies from > 3,000 m a.s.l. (remote mountain parts of Azerbaijan and Georgia) to < 0 m a.s.l. for coastal lowlands just surrounding the sea. Wide range of climatic zones locates within the watershed. It varies from continental boreal climate in upper both Rivers Volga and Ural, through step of the Southern Urals (Orenburg oblast), Mediterranean climate at Azerbaijani and Dagestan sea coasts to hot arid dessert climate in regions encompassing Kara-Bogaz-Gol bay (Turkmenistan) and southeastern Iranian shores. Moving from northwest toward southeast within the watershed, the monthly average July and January air temperatures increase from +18¸20oC to +27¸29oC and from -17¸-19oC to +4¸+10oC, respectively. Russian Volgograd city located within the lower River Volga watershed is the point of the highest ever-recorded air temperature in Russia (+43oC). Annual precipitation within the watershed ranges from 600-650 mm and 250-300 mm in the upper and lower River Volga respectively, to less than 100-150 mm at southern-eastern coast of the Caspian Sea. Russian Astrakhan' city located at the delta of River Volga is a place with the lowest annual precipitation in Russia (162 mm). The most parts of the watershed are attributed to semiarid and arid zones. Thus, southward from approx. 53oN latitude an annual evaporation exceeds precipitation. Duration of snow cover in a year cycle decreases from 150-170 days in the upper River Volga and southern Urals regions to 80-100 days in the lower River Volga and to zero values at the southern regions (Turkmenistan, Iran, southern parts of Azerbaijan) of the watershed.
Thus, the Caspian Sea accumulates river runoff from the vast territory that covers either different climatic zones or regions with various population density, economic development and pollution state.
General description of rivers
Total annual river runoff (340 km3/year - long-term average value) into the Caspian Sea is distributed between several dozen rivers inflowing the sea directly. The main rivers are Volga (Russia), Kura (Azerbaijan/Georgia), Ural (Kazakhstan/Russia), Emba (Kazakhstan), Kuma (Astrakhan/Kalmik, Russia), Terek (Dagestan, Russia), Sumgayit (Azerbaijan), Atrek (Iran/Turkmenistan), Sulak (Dagestan, Russia), Samur (Azerbaijan/Russia), Shafa-Rud (Iran), Safid (Iran), and some others. Length of the main rivers inflowing the sea is given in the illustration on the right. It should be noticed that almost all inflowing rivers are strongly regulated and affected by anthropogenic activity (mainly agricultural irrigation and hydropower plants). Particularly, River Volga is strongly regulated by valley dam reservoirs.
The Caspian Sea is the endorheic terminus of the Volga River, the longest (3531 km) and largest in watershed basin (1360,000 km2) and annual discharge, river in Europe. The river originates west of Moscow at Valdayskaya Vozvishennost' (Valday Upland) and contributes 237 km3/year on average (>80% of total inflow into the sea), with a range of 200-450 km3/year (Butorin 1979). For specific discharge it gives 5.6 (4.6-10.4) l/s×km2. The Kura River is second in line and discharges only 16.8 km3/year; the Ural River is third, with a discharge of 8.1 km3/year on average.
World Archive for Runoff Gauge Stations (WAGRS)
In 1992-98 Drs A.I.Moiseenkov and I.Nikiphorova at State Hydrological Institute (St.Petersburg, Russia) developed world Archive of Runoff Gauge Stations (WAGRS) for monthly and annually averaged river runoff data sets (Moiseenkov 2001). It was constructed in a frame of IHP (International Hydrological Program) UNESCO: "World Water Resource at the Beginning of the XXI Century" edited by Prof. I.A.Shiklomanov. Assistance and help with supplying data were rendering by Dr. V.Grabs, former Director of GRDC, Germany, and numerous colleagues from different countries as well.
Currently the WAGRS contains monthly and annually averaged river runoff data for approx. 9000 gauge stations from over the world, including 4000 stations located in the former USSR. Information available for each gauge station is as follows: 1) continent and country; 2) river and station names; 3) geographical co-ordinates and above sea level elevation; 4) river watershed area above the station (km2); 5) period of the observations and total number of months observed; 6) long-term original monthly averaged runoff data series (m3/s); 7) year-to-year (long-term) averaged annual course of i) runoff data (m3/s); ii) specific discharge from a watershed (l/s×km2).
