Impact of the European Russia drought in 2010 on the Caspian Sea level

摘要

The hydrological budgets of the Volga basin (VB) and the Caspian Sea (CS)have been analysed. The components of the water balance for the CS werecalculated for the period 1993 to 2010 with emphasis on summer 2010 when asevere drought developed over European Russia.A drop in precipitation over the VB in July 2010 occurs simultaneously witha decrease in evaporation for the same area, an increase of evaporation overthe CS itself and a drop of the Caspian Sea level (CSL). The drop in theprecipitation over the VB cannot lead to an instantaneous drop of the CSLbecause the precipitated water needs some months to reach the CS. The delayis estimated here to be 1 to 3 months for excessive precipitation in summer,longer for deficient precipitation and for winter cases. However, theevaporation over the CS itself is considered to be responsible for asimultaneous drop of the CSL from July to September 2010. The impact on theCSL from the precipitation deficit over the VB occurs in the monthsfollowing the drought. The water deficit from July to September 2010calculated from the anomalous precipitation minus evaporation over theVB would decrease the CSL by 22 cm, of which only 2 cm had beenobserved until the end of September (observed Volga River dischargeanomaly). So the remaining drop of 20 cm can be expected in the months tofollow if no other anomalies happen. In previous studies the precipitationover the VB has been identified as the main cause for CSL changes,but here from a 10 cm drop from beginning of July to end of September, 6 cmcan be directly assigned to the enhanced evaporation over the CS itself and2 cm due to reduced precipitation over the CS.Further periods with strong changes of the CSL are also investigated, whichprovide some estimates concerning the accuracy of the analysis data. Theinvestigation was possible due to the new ECMWF interim reanalysis datawhich are used to provide data also for sensitive quantities like surfaceevaporation and precipitation. The comparison with independent data and theconsistency between such data for calculating the water budget over the CSgives a high confidence in the quality of the data used.This investigation provides some scope for making forecasts of the CSL fewmonths ahead to allow for mitigating societal impacts.