Under conditions of increasing climatic uncertainty, this scientific study analyzes multi-year trends of seasonal distribution of river flow in the Zhaiyk–Caspian water basin. In specific natural conditions of the territory under consideration, under scarce water resources availability in the vast territory, and exceptional variability of river flow in time, the problem of water supply is especially important. The paper considers multi-year dynamics of runoff forming factors and flow parameters taking into account phases of different water availability. River flow estimation methods include analyses of average monthly maximum and minimum values of river flow, which allows a detailed study of seasonal and inter-annual variations. The assessmentof homogeneity of river flow series was carried out on the basis of genetic analysis and statistical analysis, application of Mann–-Kendall test, Student's t test, and Fisher criterion. The identified results indicate significant transformations in the river flow in the basin: the share of spring flow has decreased, while the share of low-water flow, especially in winter, has increased. These changes are associated with higher winter temperatures and an increase in the frequency of winter thaws. In the River Elek Basin, the share of spring flow decreased to 40% of the annual value, and in the River Or Basin, to 15%.

  • Important scientific and practical problems of hydrology are considered.

  • The impact of climate change on the transformation of intra-annual runoff is presented.

  • The influence of anthropogenic factors on the transformation of intra-annual runoff are considered.

  • Transboundary rivers emphasize the need for coordinated international water resources management.

  • Based on the calculations, the following are established: guaranteed return of water and electricity generation.

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