Nonlinear mechanisms of multi-year fluctuations of the Caspian Sea level are described. It is shown that taking into account the dependence of the evaporation layer from the surface of the Volga basin on the soil moisture content and the evaporation layer from the sea surface on its level leads to a fundamentally new (chaotic) mechanism of oscillations and the appearance of several levels of gravity. It is noted that the stochastic Fokker-Planck-Kolmogorov differential equations have a stationary bimodal level probability density. It is established that the random process characterizing sea level fluctuations at nonlinear dependence of evaporation rate on these fluctuations turns out to be non-Gaussian. The transitions induced by "noise" caused by nonlinear evaporation processes are described. A new nonlinear stochastic model of Caspian Sea level fluctuations based on predicted physical effects is proposed.
