INTRA-ANNUAL DISTRIBUTION OF RUNOFF OF TYPICAL RIVERS OF KAZAKHSTAN (ON THE EXAMPLE OF THE BUKTYRMA, ESIL, ZHAYIK RIVERS)

Global climate change and intensive economic activity lead to redistribution of the rivers water regime. The study of patterns of intra-annual distribution of river runoff is one of the most important issues of rational and integrated use of water resources. The presented research analyses long-term regional trends in the intra-annual distribution of river runoff in the catchments of the Bukhtyrma - Lesnaya Pristan, Zhabay - Atbasar, and the Ulken Kobda - Kobda from 1985 to 2022. Scientific research was carried out on the basis of statistical analysis methods using multiyear values of average monthly and average annual values of river runoff, average monthly values of air temperatures, average monthly sums of atmospheric precipitation. The multiyear dynamics of flow-forming factors and runoff parameters taking into account phases of different water availability is considered. It is revealed that on the territory of the basins under consideration there are significant changes in the intra-annual distribution of runoff, such as a decrease in the share of spring runoff, the spring runoff for the river Zhabay - Atbasar was from 63,5 % (in a low-water year) to 79,2 % (in a high-water year) in April of the annual flow, the proportion of spring flow for the Ulken Kobda - Kobda varied from 38,4 % (in a low-water year) to 71,6 % (in a high-water year), and the spring-summer flow for the period from April to July for the Buktyrma - Lesnaya Pristan was about 60…80 % of the annual flow. In terms of low-water flow, the Zhabay and Ulken Kobda rivers show an increase in the share of low-water flow, particularly during the winter period (December-March). For example, for the Zhabay, the low-water flow in winter months is less than 1 % in dry years, but its trend is positive, indicating a tendency to increase this share. The low-water flow is also increasing, for the Bukhtyrma river, although the trends are negative in January and December.