Characteristics of runoff variation in Wuyuer-Shuangyang River watersheds and their influences on Zhalong Wetlands (1956-2000), Northeast China

The current article adopts the Mann-Kendall time series analysis method to study the characteristics of the runoff variation in the Wuyuer-Shuangyang River watersheds in the past 50 years, and investigates its influences on the hydrological regime of the Zhalong Wetlands based on relevant data on the runoff variation characteristics in the Wuyuer-Shuangyang River watershed (1956-2000). The runoff in the Wuyuer-Shuangyang River watersheds in the past 50 years showed a downward trend as a whole. The drop rates of the annual runoffs of the Wuyuer River at the Bei'an, Yi-An, and Long'anqiao Stations were 69.6x10(6) m(3)/10a, 128.2x10(6)m(3)/10a, and 41.3x10(6)m(3)/10a, respectively. The runoff variation of the Shuangyang River has no significant law, and the runoff in the Wuyuer-Shuangyang River watersheds in 1970s showed an extremely low value. The annual runoff distribution nonuniformity in the Wuyuer River watershed showed an upward trend, whereas that in the Shuangyang River watershed showed a downward trend. The Wuyuer-Shuangyang River watershed is mainly characterized by the dry years, and the number of the dry years accounted for about 44.4% to 57.8% of the total number of years. The observed frequency of occurrence of the dry season in the Wuyuer-Shuangyang River watersheds was higher than that of the continuous wet season. The longest continuous wet season was live years, whereas the longest continuous dry season was seven years. The M-K analysis showed that the observed runoff of the Wuyuer River at the three hydrologic stations showed a downward-upward-downward trend, and had abrupt change points and significant changes. However, the runoff of the Shuangyang River had not mutated significantly. The runoff in the Wuyuer-Shuangyang River watersheds showed a downward trend after year 2000.