Abstract
Studies were conducted aimed at the trends in the flow of the main rivers of the Zhaiyk-Caspian water basin. The average annual dynamics of river flow for a long period, their 5-year moving averages, joint tables of air temperature and precipitation values with river flow, as well as long-term dynamics of characteristic (highest, winter and lowest in open channel conditions) water flows were considered. According to the results of the research, two periods were distinguished: from 1940 to 1973 (conditionally natural) and from 1974 to 2020. (modern). In both periods, there is a tendency to reduce runoff against the background of an increase in air temperature, precipitation trends are multidirectional. Since the 1970s, there has been a decrease in the amplitude of fluctuations in annual runoff, since the 2000s there has been a decrease in both the amplitude of fluctuations and the values of maximum water flow. In the values of the lowest summer-autumn and winter water flow, on the contrary, there is a tendency to increase, which began in the late 1980s – early 1990s. For small rivers and temporary watercourses, the summer-autumn and winter periods are periods of maximum runoff depletion, during which drying and freezing phenomena (zero runoff) are characteristic.