| Runoff change mechanisms on catchment scale has been a hot point in the field of hydrology. Kuye River, locating in northwest China, is an important trinutary of the Yellow River with features of less water, more sands and high frequency of heavy rainfall. It is the main source of flood and coarse sediment for the Yellow River, and serious in water and soil loss. Aiming at supplying basis and reference for protecting and continous use of water resource and early-warming hydro-eco of Kuye River, this article made a quantitative research of effects of runoff from human activities, and effect of water and sediment from vegetation cover changes. The achievements are as belows:(1) The runoff saltation of Kuye River appeared in 1998 for recent 55 years. It was a wet period before the saltation and a dry period after the saltation1998 is the saltation time point of Kuye River, the runoff was richer before. The especially wet period lasted from 1 to 6 years, and the especially dry period appeared in the next 18 years. The runoff presented an indifferent decline and rise in 1960-1998 and 1999-2014 respectively.The runoff of Kuye River varied in a large range with the extremes ratio of 2.5, and went down with each passing year with the deciline ratio of 1.236 × 108 m3/10a, Hurst exponent H= 0.775> 0.5. It shows that if the climate change and human activities remain the current growing trend or being more intenser in the future, the runoff will decline gradually. The runoff distributed as a bimodal pattern, the largest runoff appeared in August, about 25.5% of the annual total. The bimodal was obvious before the saltation and after the saltation. The original runoff was break and declined month-to-month.The saltation time of spring, summer, autuamn and winter appeared in 1991?1997?1987 and 1984 respectively. Among the first 3 seasons the runoff declined both before and after the saltation, but the trend after the saltation weakened. For the winter, the trend showed a rise trend before the saltation and a decline trend after the saltation, which was in accordance with the saltation rule of the year.(2) In recent 55 years, the runoff is prominently relevant to sediment load, mainly effected by the rainfall. However, in the 21th century, the contribution rate of human activities for the runoff and sediment load reached 89% and 34% respectively, which shows an enhanced human activitiesThe rainfall interannual variability of the Kuye River was 5.4mm/10a, it is an inapparent rise trend. On the time scale, the quantites of runoff and rainfall in 30a had a better closeness and similar clear rule. The wavelet variance oscillation period for both runoff and rainfall appeared at 5a,15a,30a, but the first main period of runofif was about 15a while that of rainfall was about 30a. The reference period of the double mass plot for rainfall-runoff was 1960-1978. Between 1979 and 2014, the contribution rates of human activities and rainfall for runoff were 11% and 89% respectively, and the contribution rate of human activities for runoff decline was higher than that of rainfall after the reference period.The sediment load varies acutely year-to-year. For recent 55 years, it showed a declining trend. The decline rate of sediment load was 59% after 1998 and saltated in 2001. For 55 years, the annual runoff and the sediment load had a positive correlation, which presented a decline trend before the saltation and turned negative after the saltation. The rainfall had an obvious effect on the decline of sediment load. After 1998, the effect of human activities on sediment load was 34%.(3)The NDVI showed a rise trend in recent 15 years. There was an increasing of vegetation in the observation areas,93.3% of which obtained a remarkable increasing. There was also an increasing high cover degree of the drainage basinBetween 2000 and 2014, NDVI presented an increasing trend, at the same time, NDVI changed in different areas. In this period, the maxmium NDVI appeared in summer and August, which met the same condition with the interannual; there were 94.4% of the observation area which had a positive NDVI variation slop, that is to say, in these areas vegetations increased remarkablely. The F-test showed that 93.3% of those areas changed remarkablely. the 1998 and 2009 TM images for vegetation coverage rating compared with> 10% of the four levels of vegetation coverage in 2009 increased by 939.14km?996.95km2? 348.43km2?318.78km2, vegetation coverage is increasing.(4) There is a prominent water-sand effective after the saltation.0.01 increasing of NDVI value may lead a water decreacing of 1.33 × 108m3 and a sand decreacing of 0.01 million tonThe average annual NDVI and rainfall showed a rise trend, and were significantly relevent to each other. Despite of the effect from enlarged runoff after 2012, the annual NDVI and runoff showed an unconspicuous negative relationship with each other during 2000-2011; the annual NDVI and sediment showed a conspicuous negative relationship with each other during 2000-2014. Vegetations effected the sediment load on some degree, the sediment load decreased with the vegetation increasing.Through the comprehensive analysis of vegetation, rainfall, runoff and sediment obtained:1960-1978 base period, with its 1998 boundaries mutation, mainly after restoration and water conservation measures have led to water and sediment before and after mutation, mutant vegetation after runoff the peak year (March and August) reduce the impact were 64.4% and 81.4%; and high vegetation coverage increased by 2009 over the 1998 rate of reduction of water and sediment, respectively 68% and 99.9%; the establishment of a Y runoff= 0.164Xrainfall-8.230XNDVI+2.088 and Yamount of sediment transport-1.498X runoff-0.057Xrainfall-6.544XNDVI+1.577 linear regression equation, vegetation index for each additional water can be reduced 1.33 million m3, reduce sediment 0.01 million tone. |
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