The Methodology of Long-Range Forecast
of Level and Water Balance Components of Inland Seas and Lakes

Alexey Babkin

State Hydrological Institute, St. Petersburg, Russia
e-mail: abav@mail.ru

Abstract

Large inland seas and lakes are located within arid and semi-arid zone. The water balance components and level of lakes are significantly variable. The crucial issue in modern hydrology and water resources management is the revealing of periodicities in the dynamics of lake characteristics and their account for development of the methodology of long-range forecast of lake levels.
Traditionally the methods of Fourier transform, correlation and spectral analysis are used for analysis of time series of lake characteristics. The present study develops a physically based model of oscillations of lake level and water balance components and applies it for the estimation of periodicities in their time series and their forecast computations with the lead time of 5 – 7 years.
The solution of differential equation of lake water balance permitted to develop the mathematical model of dynamics of its level, water surface area, evaporation and surface water outflow under oscillation of water inflow. The time delay of lake characteristics to the water inflow and relation of their amplitudes were calculated in dependence from the water inflow and the oscillation period for the Caspian Sea and Lake Ladoga.
The time series of the Caspian Sea and Lake Ladoga level and water inflow were approximated by periodic functions. The periodicities in the changes of these characteristics were revealed by the comparison of the results of modeling and approximation. The periodicities in the time series of water bodies were successively summed and their sums were developed into the forecast equations. The forecast estimations were received and tested by the new data.

The work is supported by the Grants of the President of Russian Federation МД-5340.2006.5 and Young Scientist Fellowship of INTAS Ref. Nr 05-109-4234.