International Journal of Marine Science, 2017, Vol.7, No.3, 19-30
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the Caspian sea water level declined with the speed of 2 centimeters per year until 1940 (between 1883-1993), and
from 1934 to 1940 it declined with the speed of 20 centimeters per year. After 1940, the sea water level falling
process slowed down and reached one centimeter per year. The process of seawater level decline, which has
dropped 3.8 meters from 1883, ended in 1977, and from 1978 the Caspian Sea started progressing with a high
speed of about 14 centimeters per year. This process continued till 1996 and in this year the water level reached
-26.52 meters. In some years, the speed of Caspian Sea water level rise reached 45 centimeters per year. This
period of water level rise has been the longest period in the era of fluctuations recording. From 1996, the Caspian
Sea water level again started its downward process until the water level reached -27 in the present time. In the era
of instrumental record, the fluctuations with the positive growth exceeded 30 centimeters three times (38
centimeters in 1867, 32 centimeters in 1979, and 39 centimeters in 1991). This index was also negative two times
(32 centimeters in 1851 and 31 centimeters in 1937). The analysis of long-term changes of Caspian Sea water
level reveals that water level in the era of instrumental record was fluctuating between the -25.2 and -29 meters; in
other words, the fluctuation range was 4 meters in this period. The frequency probability of 50 percent of Caspian
Sea water level has been defined in the -26 height during the instrumental record era. The maximal periodicity of
Caspian Sea water level fluctuations with the frequency of 55 percent exists in the level range of -25.5 to -26.3.
This range can be considered as the hydraulic index of Caspian Sea water level, and lots of scientists use the water
level mean as a criteria for calculations. Like other closed body of waters in the world, the curve of Caspian Sea
water level fluctuation is analyzed monthly and seasonally. The annual budget is determined by studying the
relation between input and output components. The maximal Caspian Sea water level has been observed in
summer and the least level has been observed in winter. The maximal fluctuation range reaches to 50 centimeters
in wet years , the least range reaches to 15 centimeters in dry years, and the measured range is -29 centimeters.
Figure 8 The Caspian Sea datum in the period of instrument-aided observations according to the data of Baku sea gauge
Average annual levels of the Caspian Sea in the instrument-aided observation period of 1930-2010 are shown on
Figure 8. As it shown by the figure in 1830-1930 the average annual sea level varied approximately within
one-meter range. Sea level high stands at 25.4 m in the Baltic System and above this level were observed in 1838
and 1939, in 1868 and 1869 and in 1877-1883. In 1882 the average annual level reached 25.2 m (maximum in the
observation period). Relatively low sea level of -26.2 m in the Baltic System was observed in the 50s of the last
century and in 1911-1914. The highest drop of the sea level to -26.6 m was observed in the last year of 1920-1925
period. Sea level datum in 1830 - 1930 was -25.83 m in the Baltic System or 340 cm above zero level of Baku
depth gauge in 1920 elevation. Relative equilibrium state of sea level was followed by the period of abrupt drop in
1930-1941 by 1.9 m. The sea level drop although not such strong was resumed in the end of the 40s; in 1956 sea
level was by 2.5 m below the 1929 level. In the 60s the sea datum stabilized at the level of around -28.4 m and in
1970 the sea level abruptly dropped and reached -29.0 m in 1977. Total drop in the entire period of systematic
