Results of the theoretical and the experimental investigations of soil water regime for the winter-spring period in mainly for regions of steppe and forest- steppe zones are obtained.

The theoretical part of work is based on mathematical modelling of heat and water transport in the system atmosphere - snow cover - frozen soil - thawed soil. A complex of physical-based models of principle hydrological and geophysical processes was created. Models were created by using an integral balance method that allows to incorporate physical principles in relatively simple mathematical formulations. The essence of the method consists in that, when solving the problem of the vertical distribution of the pertinent characteristics of the water and heat regime of the soil (for example, soil moisture or its temperature), an approximation of this distribution by a certain polynomial with respect to the vertical coordinate with undetermined, time-varying coefficients, for finding which boundary conditions and balance equations in an integral form are employed, is used. Complex of created models includes models for freezing soil, upgoing water migration flow from thawed zone to frozen one, dynamics of soil temperature profile, water infiltration into frozen soil, thawing soil following snow melting.

The observed hydrological and hydrometeorological data of set of water-balance stations of forest, steppe, and forest-steppe zones (Podmoskovnaya, Nizhnedevitskaja, Bolkhov) were also used for validation and verification supposed models. Field experimental investigations have also been carried out in the area of the Kursk Biosphere Station (forest-steppe zone).

A comparison was carried out of calculated and observed results for freezing dynamics, temperature and moisture distribution in soil, total amount of infiltrated water, and daily slope runoff intensities. The depth of freezing was determined by a Danilin cryopedometer for many years series for above mentioned stations. Measured data of moisture dynamics were taken from the materials of observing moisture on these stations. Soil temperature was determined on the Kursk Biosphere Station and the Nizhnedevitskaja water-balance station by means of electrical thermometers located at different horizons in the soil profile. Observed runoff hydrographs data were taken on two field plots of the Podmoskovnaya water-balance station and four field plots of the Kursk biosphere station. The measurements and calculations indicate satisfactory agreement.

Yeugeniy M. Gusev
Institute of Water Problems, Russian Academy of Sciences,
Novobasmannaya st. 10, Box 524, 107078 Moscow, Russia
Telephone (095) 265-95-85