The article is devoted to the study of climate change in the Sula River basin and its impact on the river’s water availability. To analyze changes in the runoff of the Sula River, the water balance method was applied; evaporation was calculated using Konstantinov’s method, and aridity and runoff coefficients of the Sula River, as well as Pearson correlation coefficients, were determined. It is established that the Sula River has been characterized by a low-water phase lasting since 1989, and a persistent downward trend is observed for all quantitative characteristics of river runoff. Mean annual air temperatures during the period 1979–2020 show a stable upward trend, as do indicators of total evaporation; in contrast, a weak downward trend is observed for annual precipitation totals. An analysis of the components of the water balance equations of the Sula River basin for the periods 1979–1999 and 2000–2020 showed that annual atmospheric precipitation remained almost unchanged (a decrease of 1.8%), evaporation increased by 7.1%, and the runoff layer significantly decreased by 43.3%. The calculated correlation coefficients between the mean annual discharge of the Sula River and mean annual air temperature, as well as between minimum water discharge and sunshine duration, indicate an inverse correlation (correlation coefficients of -0.61 and -0.63, respectively). The relationship between the mean annual discharge of the Sula River and annual precipitation indicates a direct dependence (correlation coefficient of 0.38). A decrease in the runoff coefficient during the second observation period compared to the first period by more than one third is accompanied by a regular increase in the aridity coefficient of 7.3%.
Sula river; runoff; water discharge; runoff layer; mean annual air temperature; precipitation; evaporation