Runoff Variation and Its Effect on Statistical Characteristics and Frequency of Runoff in the Upper Reaches of Heihe River Basin

【Objective】 Statistical characteristics and frequency of runoff is crucial for water resources planning and water resource project construction, especially when runoff in watersheds shows significant variation due to environmental changes. Taking upper reach of the Heihe River basin as an example, this paper examines the impact of runoff variation on statistical characteristics and frequency of the runoff analysis. 【Method】 Annual runoff and annual maximum flooding flow measured from the reach were used in our study. Two types of analysis windows, the fixed-point variable-width window (Type A window) and the variable-point fixed-width window (Type B window), were used to extract the runoff sequences (window sequences) for analysis. The P-Ш type curves were utilized to analyze the statistical characteristics of the window series, from which we calculated the runoff design values. The trends and discontinuity in the window series were identified using the linear trend analysis, MMK trend test, and heuristic seg