Research On Periodicity Of Annual Runoff In North Region Of Shaanxi

Analysing the periodicity of runoff series, has a certain theoretical value for understanding the evolution of hydrology, hydrological forecasting, water resources assessment and management,and promoting sustainable utilization of water resources have important practical significance.Taking Northern Shaanxi as the study area, based on 8 major rivers in the study area 12 hydrological stations measured runoff data for nearly 60 years,it used hydrological variability diagnostic system has detected a series of measured runoff variability; according to the theory of random revised variation components of the observed runoff series; based on the Maximum Entropy Spectral Analysis, Wavelet Analysis and Hilbert- Huang transform methods calculated respectively periodicity of before and after the amended runoff series. Major conclusions are showing here:(1) Using the Hydrologic variability diagnostic analysis detected the measured runoff series in Northern Shaanxi and revised variation components. Results show that the runoff series have significant downward and mutated,except the Yanchuan staion. Through comprehensive analysis of the coefficient of variation, we find that Huangfuchuan, Gushanchuan, Tuweihe, Kuyehe(Wen Jiachuan station) and Wudinghe(Baijia Chuan station) mainly have trend variation, while Kuyehe upstream(Shenmu station), Jialuhe, Wudinghe upstream(Zhaoshiyao station and Dingjiagou station),Qingshuihe and Yanhe mainly have mutaion variation.(2) Using Maximum Entropy Spectral Analysis method to analyze the measured and variation revised runoff series. The results showed that both the period characteristics of the measured and revised runoff series by the Maximum Entropy Spectral Analysis method within 10 years scale were consistent, there were 3 and 9 year periodic variations of the runoff in in Northern Shaanxi.For over 10 years periodic variations,it is poorer to recognition on the consistency, only part of the stations detected over 10 years period, and it failed to detect periodic variations of the Gaojiapu station observed runoff.(3) Using the Wavelet Analysis method to analyze the observed and variation revised runoff series. The results showed that both the period characteristics of the measured and revised runoff series by the Wavelet Analysis method within 10 years scale were consistent, there were 3 and 9-10 years periodic variations of the runoff in in Northern Shaanxi.To the variation revised runoff series,there are 7 stations which be detected to have over 20 years long period. To the measured runoff series,there are 12 stations which be detected to have over 20 years long period,and most mainly concentrated in 28-31 years.It showed that the variation component may influence on the recognition of periodicity by the Wavelet Analysis.(4) Using Hilbert- Huang Transform method to analysis analyze the measured and variation revised runoff series. The results showed that both the period characteristics of the measured and revised runoff series by the Wavelet Analysis method were almost consistent, there were 9 stations which been detected about 28 years periodic variation.There were 3 and 9-10 years periodic variation of the runoff in in Northern Shaanxi,and the runoff series of most stations have 20 and 28 years periodic variation. The method is comprehensive to identify the periodicity of the runoff,which were uniformly distributed within 10 years, 10-20 years, and over 20 years scale.(5) Comparative analysis the results by three methods analyszing the measured and variation revised runoff series, showed that in Northern Shaanxi area runoff generally have about 3 years, 9 years, 20 years and 28 years around period characteristics. Within 10 years, results of the measured and revised runoff series by the Maximum Entropy Spectrum Analysis and Wavelet Analysis are almost consistent,but results over 10 years is poorer consistency. The periodic analysis results of the measured and variation revised runoff series based on the method of Hilbert Huang Transform is consistent,and it has strong adaptability to the runoff series which in changed enviroment,so the Hilbert Huang transform method can be used to hydrological in changed environment period analysis.