Tendency and Periodicity of Annual Runoff of Naoli River from 1956 to 2005
1956年～2005年挠力河径流演变特征及影响因素分析

The largest and most concentrated wetland region in China is in Sanjiang Plain in the northeast of China, and Naoli River is a typical marsh river in Sanjiang Plain. The changing tendency and periodicity of its annual runoff were affected by climate changes and human activities. In this paper, the Mann-Kendall test for trend detection and wavelet analysis were used to analyze the tendency and periodicity of annual runoff in two hydrological stations (Baoqing station and Caizuizi station) in the past 50 years. The results showed that: the annual runoff of both hydrological stations declined remarkably, and the declined tendency of summer flood season in Baoqing station and spring flood season in Caizuizi station were most obvious. The long-term time series cycle of annual runoff is about 45 years in Baoqing station and about 40 years in Caizuizi station. With more energy, the short-term time series cycle of annual runoff is about 15 years in Baoqing station and about 25 years in Caizuizi station. At present, Naoli River watershed is in dry season, and its wet season may come in the year 2020. Tendency and periodicity of annual runoff were mainly influenced by climate changes and human activities. Precipitation decrease and temperature increase were the main aspects of climate changes, and the impact of human activities was mainly embodied by the large reclamation area of marshland and the construction of water conservancy projects in the watershed area. During the past 50 years, the underlying surface of watershed has greatly changed. Nearly 40% of the watershed was covered by marshland in 1950s, however, till 2000, about two thirds of the marshland had been cultivated, 80 percent of which was cultivated into farmland. Therefore, the landscape matrix has changed from marshland to cropland. About 40 reservoirs were constructed, which also has tremendous impacts on the process of water cycle. But more efforts should be devoted to quantitatively analyze the impacts of wetland and the construction of water conservancy projects on the characteristics of runoff.