Seasonal dynamics of small river flow in the forest-steppe zone of Nizhny Novgorod region in extremely low-snow winter based on the Medyana river case study

Abstract

The present study examines the interseasonal dynamics of small river flow in the forest-steppe zone of the Nizhny Novgorod region during the extremely low-snow winter of 2024-2025, using the Medyana River as a case study. Observations were conducted at two hydrological stations established in the upper and lower reaches of the river during the spring flood and summer low-water periods. The "velocity-area" method was used to determine water flow in the river. The results of the study showed a significant decrease in river flow during the spring flood in 2025 compared to 2024: a 23% reduction in the upper reach of the Medyana River and a 73% reduction in the lower reach. However, the minimum flow rates during the summer low-water period increased by 4% in the upper reach and by 66% in the lower reach. These changes may have been caused by a sharp rise in temperatures during the winter, leading to an increase in thaws that affected the reduction of the frost depth in the aeration zone and a decrease in snowpack by the time of snowmelt. This, in turn, resulted in a reduction in surface runoff and a redistribution of meltwater toward groundwater. Consequently, these factors led to a decrease in maximum water flow during the flood period. On the other hand, the increase in groundwater reserves, which support the river during low-water periods, resulted in a sharp increase in low-water flow.