Abstract: To reveal the hydrological evolution patterns of Yahekou Reservoir Basin in Nanyang City, Henan Province, and provide a scientific basis for its water resources management and flood regulation, we analyzed precipitation and runoff data from 1960 to 2024. Using the Mann-Kendall test, cumulative anomaly analysis, and 5-year moving average method, the intra-annual and inter-annual periodic variations of rainfall and runoff within the reservoir basin were investigated. The Morlet wavelet transform was further applied to examine the periodic characteristics of precipitation and runoff. The results indicated that the monthly precipitation distribution within the Yahekou Reservoir Basin was uneven, and monthly runoff varied significantly, with approximately 77% of the annual rainfall and runoff concentrated during the flood season. Both annual precipitation and runoff exhibited considerable fluctuations over the years, overall showing a declining trend, with their variation patterns tending to be consistent. Statistically non-significant abrupt changed in precipitation and runoff occurred around 2010 and 2012, respectively. Before the abrupt changes, both showed an oscillating upward trend, which shifted to a downward trend afterward. Additionally, precipitation and runoff displayed four primary periodicities, which were 55, 34, 19, and 8 years, corresponding to variation cycles of approximately 35, 20, 11, and 6 years, respectively. The periodic variations of rainfall and runoff were essentially synchronous, with the first primary periodicity being 55 years for both.