| Soil erosion and river water and sediment dynamics is one of the important scientific issues in today’s Earth Surface Processes Research. Soil erosion,water and sediments dynamics are closely related to the local rainfall and vegetation conditions. Loess Plateau hilly region is one of the most serious soil erosion areas in the world,it has great meaning to research among vegetation, rainfall and erosion for understanding changes in soil erosion and carrying out erosion control work in eroded areas. The study of this paper is Yanhe River basin which is a typical representative of the Loess Plateau gully area, the research datas in this paper are mostly from meteorological and hydrological station during1956-2010and1995,2000,2007and2010in Yanhe River,the main methods are Mann-Kendall non parametric statistical tests, Morlet wavelet analysis, quantile regression (QR) method, discussed the changing trend and relationships of rainfall, land cover and runoff sediment, explored the adaptability of the QR method in the study of Hydrology in the Yanhe River basin, and analyzed precipitation and land cover change on spatial and temporal effects of watershed runoff and sediment transport. The results are as follows:(1)The precipitation in YanHe River basin has been decreasing during1956to2010, and the mutation time occurred in1991, after that it started to decline,after1956there was a significant decline and had28a shock cycles. Flood season started from June to September accounting for68.43%of annual precipitation,and July to August rainfall accounted for60.8%of the entire flood season. The average annual precipitation had a little spatial variation in YanHe River basin, the precipitation in the southwestern region had a slightly declining trend while in the northwest and the southeast region had a weak ascending trend, but the it was not obvious. The extreme average precipitation is22.9mm in YanHe River basin, among them, the precipitation in Yan’an, Ansai are more than26mm, Ganguyi is21.3mm, Zhidan is17.4mm, and Jingbian is14mm. Most extreme rainfall focuses on the flood season (June to September), which took37%-75%of the annual extreme precipitation.The extreme precipitation in Yanhe River changed obviously, and intergenerational differences became increasingly apparent in precipitation from southeast to northwest.the periodic changes were obvious, the longest period is about 18a, and4a and5a had shorter cycles in individual years. Extreme precipitation was unevenly distributed in space, the average annual extreme precipitation and precipitation frequency had decreased from southeast to northwest, precipitation intensity reinforced from the central region to the northwest and the southeast.(2)The runoff and sediment in YanheRiver basin showed a overall trend of decline from1956to2010, but large differences in various years. Among them, there had a high runoff between the1950s to the1960s, it was relatively stable after the1960s to the late20th century and a sharp decline in the early decades of the21st century. According to the research of the mutation Year and comparison contrast of the runoff and sediment,so the1956-2010annual runoff and sediment discharge basin classified as non-significant change period, the year between2001and2010as a period of significant change.(3) The vegetation NDVI showed weak growth trend in Yanhe River basin from1982to2006, vegetation cover declined from1983to1987; vegetation cover rising rapidly in1988-1990,with characteristic of small-scope fluctuation of relative stability in1991-1998;The vegetation cover rose sharply from1999to2006. The difference of watershed vegetation NDVI in1982-2006yearly distribution was prominent. Watershed average NDVI began to rise from March, the rapid growth in July, in August and September,its got the the highest value, the growing season, from May to October, NDVI values were all greater than0.2. The change of watershed vegetation NDVI existed space differences.Woodland vegetation cover in southern regions have significant decreasing trend,in the northwest and central areas of grassland and grassland area’s vegetation coverage has increased significantly.From1995to2010in Yanhe river basin, Grasslands and unused land area’s area in number was biggest,the grasslands with the rate of a year of2.62%to grow on average, unused land area by an average4.42%to reduce. The types of land utilization is always given priority to the grassland, which covered an area more than40%of the whole drainage area, woodland and farmland were in second place. In the aspect of dynamic degree of land utilization type, as a whole, the growth of urban land with the maximum of5.07%,the decline of unused land with the maximum of4.42%,grassland, cultivated land, and water were in second place, the change in the minimum is the forest of all land utilization type.(4)Compared with the monthly precipitation,NDVI have one month lag in YanHe River basin from1982to2006. we conclude that two standard precipitation and NDVI were highly significant positive correlation and the correlation levels were0.44and0.15By comparing the basin annual precipitation, extreme precipitation and average annual growing season NDVI; the spatial distribution of the northwest showed a significant positive correlation and the southeast was weak negative correlation. Compared with non-significant change period (1956-2000), the Significant change period (2001-2010) showed that the average water sediment basin,the value of standard deviation and coefficient of variation have a significant downward trend, while the precipitation and extreme precipitation have the same amount of variation, there was a significant positive correlation among the three, in which the correlation coefficient between precipitation and runoff was0.68, the correlation coefficient of extreme precipitation and runoff was0.41,to the sediment were0.52and0.23. Sediment and runoff had a significant positive correlation from2001to2010, Where runoff and sediment showed maximum correlation coefficient (R2=0.85) during the wet years, dry years followed (R2=0.44), the flat water was lowest (R2=0.18); According to the amount sediment size,we can judge the runoff sediment carrying in different years.In wet years the capacity of runoff was the largest, Its capability was2.24times and4.93times to flat water and dry years in carrying sediment. Vegetation NDVI and river runoff and sediment showed overall positive correlation in YanHe River basin from1982to2006, and their correlation coefficient was0.35, it was quite different in the correlation in different stage. During1982-2000they were positively correlated and during2001-2006they had a negative correlation overall.(5) Annual precipitation, runoff, sediment had different degrees of stability, get short-term fluctuations in the model, its goodness of fit was much better than the long-term equilibrium model of goodness, and former term deviation from the long-term period.the difference between the balance will be corrected at a later stage reverse. Annual runoff, sediment transport in response to annual precipitation increased with annual precipitation gradually increased, but at a high level part of the effectiveness of QR are better. The actual sequence of Meteorology and Hydrology heteroscedasticity, trend, cointegration, QR analyze data more in line with the actual characteristics of meteorological, hydrological,it has stronger data mining functions. |
PDF Full Text Request