Abstract
<jats:p>The paper presents the results of statistical analysis of maximum water discharges and highest water levels in the Yesil River basin within the Republic of Kazakhstan. Source hydrological observation series cover the period from 1935 to 2023 at 30 gauging stations located on the main channel and tributaries. Missing data were reconstructed using the hydrological analogue method with linear regression equations; correlation coefficients ranged from 0.70 to 0.99. Statistical parameters – mean value, coefficient of variation (Cv), and skewness coefficient (Cs) – were determined by the method of moments. Empirical and theoretical frequency curves were constructed using the Pearson Type III distribution. Design values of maximum discharges and highest water levels at exceedance probabilities of 0.1, 1, 5 and 10% are established for hydraulic engineering design. Long–term trend analysis reveals a gradual decline in peak water levels since the 1990s, consistent with regional climate change signals.</jats:p>