The Assesment of Variabilities in the Climatic Regime Over the Caspian Sea Level Fluctuations from Topex/Poseidon

Caspian Sea (CS) has long been the focus of an interest due to its considerable water level fluctuations. The primary factor contributed to the sea level variations has been usually deemed to changes in climatic parameters. We analyzed approximately 13 years of Topex/Poseidon (T/P) data to compute temporal mean water level fluctuations from December 2002 to August 2005, using the new Gravity Recovery and Climate Experiment (GRACE) orbits. Four distinct trends in water level variations are observed: (i) sea level rise with a rate of 19.5 ± 1.2 cm/yr between 1993 and mid-1995, followed by (ii) an abrupt decline in a ratio of -24.2 ± 0.7 cm/yr from mid-1995 to August 1997, then (iii) relatively modest decrease of -6.5 ± 0.9 cm/yr until August 2002, and (iv) average increae of 9.9 ± 1.5 cm/yr onwards. The increased inflow from Volga River in combination with increased precipitation and decreased evaporation over CS could be responsible for water level rise between 1993 and 1995. The sudden drop in the Volga runoff might be the main reason in the water level decline after 1995 despite the continued increase in the rate of precipitation onto the Volga basin. Another mechanism attributed to the CS water level decline may be the transfer of CS water to the KBG bay through opening the dam in the KBG strait in 1995. CS surface height decrease at a relatively smaller rate between 1997 and 2002 could probably be caused by increased evaporation – during this period, the discharge of Volga River was almost stable. Moreover, enhanced precipitation on the Volga catchment and decreased water consumption in the Volga drainage basin from 1991 to 2001 may suggest that evaporation over CS could have played a dominant role in sea level drop in the second half of the 1990s.