Estimating the Caspian Sea Level and Volga River Runoff from Satellite Altimetry
Kostianoy, A.1; Lebedev, S.2; Cretaux, J.3; Vignudelli, S.4
1P.P. Shirshov Institute of Oceanology; 2Geophysical Center; 3Lab. d'Etudes Geophysique et Oceanographie Spatiale; 4Consiglio Nazionale delle Ricerche, Istituto di Biofisica

The Caspian Sea is the world’s largest isolated water reservoir. Over the past half-century, there was a regression of the Caspian Sea until 1977 when the sea level lowered to -29 m. In 1978 the water level started to rise rapidly, and now it has stabilized near the -27 m level. About 80% of the total riverine runoff to the Caspian Sea is provided by the Volga River with a runoff of 240 km3/year in average but with a strong interannual variability. Its effect is a significant change in the freshwater balance of the sea with consequent oscillations in the surface level. The in-situ sea level observation infrastructure was based on 79 gauge stations in 1960 which decreased to 51 in 1972, 36 in 1992 until 3 in 2004 in the Russian side with the addition of 4-5 stations in other Caspian countries. In addition to decreasing in number these stations usually provide information on sea level change only nearby the coastline. This has a significant impact on the measurements as some gauges exhibit a positive vertical lift, which introduces considerable error in the interannual variability of sea level. Satellite altimetry can overcome these problems. The aim of this presentation is to show what we learned from applying satellite altimetry (TOPEX/Poseidon and Jason-1 data sets from 1992 to 2006) to the investigation of seasonal and interannual variability of the Caspian Sea level. Special emphasis will be given to the estimation of the Volga River runoff from satellite altimetry.


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