Caspian sea level from Topex-Poseidon altimetry: Level now falling

Tide gauge measurements recorded between 1978 and 1993 indicate that the Caspian sea level (CSL) has been rising at an average rate of ~12cm/yr during this 15-yr time span. Decadal CSL changes are currently attributed to changes in river runoff and effective evaporation. We have analysed three and a half years (from January 1993 through August 1996) of altimeter range data from the TOPEX-POSEIDON mission over the Caspian sea to estimate temporal variations in the sea level. We show that the Caspian sea level was still rising at a rate of 18.9+/-0.5cm/yr between January 1993 and July 1995 and that the northwestern Caspian in the area of the Volga delta was rising faster (by ~3cm/yr) than the middle and south Caspian. However, by mid-1995, the CSL started to drop abruptly, a trend still observed in 1996. The average sea level decrease recorded from mid-1995 amounts to -24.8+/-1.4cm/yr.