Analysis and Assessment of the Trend of Changes in the Hydrological Regime of Rivers in the Water Catchment of the Nura River Basin

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.