| The interactions and the result of Rainfall-runoff-sediment is today’s frontier of global change and soil and water conservation research. In this paper, the Loess Plateau as an object, the precipitation, runoff and sediment transport in the12basin were collected to analyze the basic variation and their relationships. Delineation of the major sources of regional runoff, sediment, and soil and water conservation for the region provides research support, the main conclusions are as follows.(1) the annual precipitation are decreasing in Loess Plateau, and the high concentration, the annual rainfall is455.7mm, flood season precipitation is340.1mm, the ratio reached up to74%; the trend rate was-11.1mm/10a; The cumulative analysis concluded that interannual variability of precipitation performance of the wet (1955-1976years) fluctuation stability (1976-1996)-the dry period (1997-2009), MK further analysis confirmed that the rainfall had a significant changes in1976;wavelet analysis shows that there is a variation of precipitation in multiple time scales, the first primary cycle of pricipitation is28-year time scale, the second main period is13-year-time scale, these two cycles exist throughout the period, but the third main period of7years in the1975-2000.(2) The annual runoff of the Loess Plateau is3.57billion m3, flood season runoff is2.02billion m3, flood value accounted for60.2%of the annual average, the trend rate is-7.36m3/10a. Wudinghe, Beiluo, Kuye River, Yan River and Tuweihe are accounted for81.01%of the average annual runoff, the percentage of each basin were:28.93%,23.69%,13.36%,8.54%, and5.77%. Cumulative runoff anomaly analysis, the wet and dry transformation among Wuding, Kuye and Huangpu is consistent with precipitation. However, Yan River, Beiluo and Tuweihe only with alternating wet and dry again.The further MK analysis showed that the significant changes occurred in1999, but Tuweihe occurred in1985, Beiluo had never occurred significantly reduce; Shaanxi North Loess Plateau, the first primary cycle average of runoff is9-year time scale, the second and third main period is22years and5-year time scale, the third primary cycle in various basins in is basically consistent with the Loess Plateau, there are only exist before1999. The first two main cycles also have differences among the basin, indicating that there are c certain differences cycle characteristics of each basin. (3) The annual sediment of the Loess Plateau is401million t, flood season sediment is385million t, flood value accounted for96%of the annual average, the trend rate is-122million t/10a. Which Wuding, Kuye, Beiluo, Yanhe and Huangfuchuan percentage of total annual sediment of up to77.3%, the percentage share of basins were:19.7%,18.9%,16.6%,12.3%and9.7%; The sediment accumulation anomaly analysis showed that:the wet and dry transformation among Huangfuchuan and Kuye is consistent with precipitation. Yan River and Wudinghe had twice alternately wet and dry. Tuweihe and Beiluo, there are a stable period among alternating wet and dry; MK Further analysis showed that:the significantly reduce of the Loess Plateau in2005, Huangfuchuan, Kuye River, Tuweihe this time in2001but Yan River, Wudinghe and Beiluo had no significant reduction. The three main changes cycle are:21-23years and4-5year-time scale changes. Howeverthree time scales changes in each basin are different, Shaanxi North Loess Plateau, the first primary cycle average of sediment is12-year time scale, the second and third main period is23years and5-year time scale. There are differences in each basin:Wuding, Huangfuchuan and Beiluo the first primary cycle is12-13year time scale, the second main period is23-year time scale, but the main second period of7-year time scale in Huangfuchuan. Kuye River and Tuweihe first main period of25years time scale, but the second, three main cycles had changed.(4)The relationship between water and sediment fitting much better in the main sediment yield area than in the other tributaries. But the fitting correlation of Beiluo River was not good. The Water and sediment collaborative relationship of both the Loess Plateau and tributaries presented convergence-attenuation trend. However Water and sediment collaborative relationship of Huangfuchuan was highly consistent in the period. |
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