Abstract

The Caspian Sea Level (CSL) shows major fluctuations on different time scales ranging from days to decades. In particular the long-term variation has been the subject of many studies and debates. It is controlled by a delicate balance of water inflow from rivers (mainly the River Volga) and direct precipitation onto the Caspian versus evaporation of water from the sea surface. Human water extraction from the drainage basin and the outflow of water to the Kara-Bogaz-Gol (KBG) are of minor influence but cannot be ignored. This paper gives a prediction of the future CSL for the period 2010-2050. As a first step a rainfall-runoff model is set up, which expresses the river outflow as a linear function of the precipitation, vapor pressure deficit and human water extraction in the drainage basin. Another function is set up to express the outflow to the KBG as a function of the CSL. The future CSL is computed using output data from 18 different Global Climate Model (GCM) runs of the CMIP3 generation and by considering a distribution of possible scenarios for the future human water extraction from the drainage basin. A Monte Carlo approach is adopted that considers both long-term uncertainties associated with 18 GCM runs and 3 future water extraction scenarios, as well as short-term variability associated with weather uncertainty and year-to-year fluctuations in human water extractions. It is found that the 50% (median) CSL prediction shows a gradual drop from 0.75 m CD in 2009 (=0.75 m above Caspian Datum) to -0.34 m CD in 2050.

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