Abstract
To study the spatial and temporal variability of the mean annual river discharge within the Nura River basin, long-term hydrological data from the monitoring stations Bes-Oba, Sheshenkara, Balykty, Akmeshit, and R. Koshkarbayev, as well as from the rivers Sherubainura, Sokyr, Akbastau, Ulken-Kundyzdy, and Kon, were utilized. These stations are relatively evenly distributed across the basin, covering an area of 58,100 km², with observation periods spanning from 1932 to 2021. The analysis of hydrological process dynamics within the Nura River basin watershed reveals that long-term fluctuations in mean annual river discharge comprise both stochastic and deterministic components, the latter represented by a linear trend. Statistically significant estimates of the parameters characterizing the cyclic structure of long-term fluctuations in mean annual river discharge (phase, amplitude, and synchronicity) were obtained. It has been demonstrated that the alternation of high-water and low-water years, associated with the phases of long-term discharge fluctuation development, can be represented as time-dependent functions exhibiting dynamic means with varying intensities. This phenomenon may serve as a scientific basis for river discharge forecasting.