Regularities in the Formation of Surface Flow of Snowmelt Water from Plowed Lands of Different Types in the Forest-Steppe and Steppe Parts of the Don and Volga Basins

Long-term experimental data collected by the authors were analyzed to characterize the formation of spring surface flow in different natural zones of the Volga and Don basins with the use of water-balance method (hydrologic experimental plots) for its treatment, and literary data on such studies were generalized. The obtained unique material was used to characterize the surface runoff separately from loose and compacted plowed lands and to evaluate the runoff-regulating role of the fall tillage of soil. The analysis of theoretical curves of runoff exceedance probability showed that its mean values and the different exceedance probability decrease from N toward S and SE, and the difference between the loose and compacted plowed lands increases. However, in some years, runoff inversion can be seen, i.e., its volume in the forest-steppe zone is less than in the steppe zone, where it can be high. This suggests that the effect on runoff formation produced by anthropogenic factors is less than that of natural factors, forming under different climate conditions, varying over zones and years.