Abstract
Global and regional climate change and their water-related impacts are a key component in future development scenarios to guide sustainable water management. Climatic changes may lead to an undesirable redistribution of water supplies and potentially harmful extremities in river flows throughout the year. If we add to this the uneven spatial distribution of water resources in Kazakhstan, the importance of assessment of the intra-annual distribution of river flows under historical and present climatic conditions becomes evident. The presented scientific study analyzes decadal regional trends from 1985 to 2022 in the intra-annual distribution of river runoff in selected catchments in Kazakhstan, including Buktyrma River, Zhabay River, and Ulken-Kobda River. The river basins were selected to cover diverse regions in terms of geographical features and hydrological conditions, significantly affected by climate change. We applied statistical analysis methods using multiyear values of mean monthly and mean annual river flows, mean monthly air temperatures, and mean monthly precipitation. To analyze the intra-annual distribution of annual river flow in the context of climate change, a computational method was used, in which the actual current river flow (modern river flow taking into account non-stationarity of climatic changes) was compared with the conditionally natural flow obtained by modeling and corresponding to the natural regime of the river. The long-term dynamics of flow-forming factors and runoff parameters with regard to phases of different water content (25%, 50%, and 75%) were considered. Statistical analysis of seasonal changes in water content of modeled and actual river flow, taking into account climatic non-stationarity, allowed us to identify significant trends of flow redistribution within the year: indicating a decrease in the volume of spring floods, an increase in winter flow and increase in seasonal variability, especially for the Ulken Kobda River. It appears that atmospheric circulation significantly affects annual and seasonal variations of water availability. The shift in western circulation type (W) contributes to increased average annual river flow, while the shift in eastern circulation type (E) is associated with amplification of extreme flood-type events. The results obtained are important for adapting sustainable water management practices under a changing climate, helping to anticipate the availability of water resources and allowing pro-active measures to mitigate hydrological extremes.