Assessment of Recent Short-Term Water-Level Fluctuations in Caspian Sea Using Topex/Poseidon

The Caspian Sea (CS) has long been the focus of an interest due to its large water-level fluctuations. The primary factors of the CS water-level variations have usually been deemed to changes in climatic parameters. The climate-induced changes particularly in precipitation over the Volga River catchment and evaporation over CS mainly affect the CS level (CSL). We constructed extended and refined TOPEX/Poseidon time series to compute temporal mean water-level fluctuations from December 1992 to August 2005 over CS using the new gravity recovery and climate experiment orbits data, new sea state bias model, and TOPEX microwave radiometer drift correction. Four distinct phases in water-level variations are observed: a significant water-level rise between 1993 and mid-1995 followed by an abrupt decline from mid-1995 to summer 1997, then relatively modest decrease until mid-2002 and rise from summer 2002 onward. The analysis of water budget parameters favors the recent understanding that Volga River discharge in conjunction with evaporation over CS are the two main components controlling water-level fluctuations of CS. Volga River discharge positively correlates with CS water-level rise and drop from 1993 to 1997 and in 1999, respectively. Evaporation should dominate over the Volga River runoff and primarily controls CSL fluctuations after 1997 through 2003. Additionally, we find that anthropogenic factors are insufficient to affect water-level oscillations except for reservoir development or demolition, and water-level changes during 13-year time series are temporary variations.