Tilo Schöne (GFZ German Research Centre for Geosciences, Germany); Julia Illigner (GFZ German Research Centre for Geosciences, Germany); Christian Gruber (GFZ German Research Centre for Geosciences, Germany)

The Caspian Sea level (CSL) has been subject to fluctuations of more than 2.5 m during the last 40 years. Since 1993 satellite altimeters have monitored fluctuations of more than 1.5 m – multi-annual fluctuations until 2005 and persistent decreasing lake levels in the order of 10 cm/year afterwards with trends of -11 cm/year in the North and -9 cm/year in the South. According to previous studies on these time scales the CSL is dominated by the balance between river (mainly Volga) discharge and net evaporation over the Caspian Sea. However, to some degree also tectonic forces and subsidence due to oil/gas production might be contributing to observed CSL changes.
Changes of the water amount in the Caspian Sea can also be monitored by gravimetric measurements from the GRACE satellites. Time series of equivalent water heights of the Caspian Sea originating from 5 different processing centers were retrieved from the EGSIEM – Plotter (plot.egsiem.eu) and, in addition, from the JPL-mascon solution. While the annual signal of the altimetric and gravimetric data are very close to each other, the trends from 2005 onwards of the equivalent water heights and the sea level from altimetry disagree. Depending on the solution the gravimetric trends account only for 75-50% of the altimetric trends. The reasons for the discrepancies between the two data sources are further investigated.