Quantitative study on runoff effect of seasonal frozen soil in mid-high latitude cold region

ABSTRACT To quantify the runoff response of seasonal frozen soil in mid- to high-latitude cold regions of China, this study focuses on the upper Naoli River basin in the Sanjiang Plain. Methods including Sen's slope trend analysis, the Mann–Kendall test, and moving correlation analysis were used to assess freeze–thaw characteristics and long-term precipitation–runoff dynamics. Calculation formulas were developed for soil water storage during freezing and water release during thawing. Results show a clear trend of frozen soil degradation, with the freeze–thaw cycle shortening at a rate of 0.62 d·yr−1. Annual precipitation and average runoff decreased by 0.226 mm·yr−1 and 0.112 × 108 m3·yr−1, respectively. Monthly runoff coefficients peaked in April and November, reaching 0.98 and 0.59. During the non-frozen period, both precipitation and runoff coefficients declined synchronously. In contrast, runoff coefficients during the freeze–thaw period decreased significantly, especially during thawing, while precipitation remained relatively stable. The soil water storage ratio during freezing showed an increasing trend, averaging 62.09%; the release ratio during thawing showed a decreasing trend, averaging 54.06%. These findings provide a scientific basis for further research on seasonal frozen soil runoff effects in cold regions.