Assessment Of Impact Of Human Activities On Runoff And Sediment Load Within Paired Years With Similar Weather Condition In The Yellow River

The environment effect of climate change and human activities is hot issue in the fieldof geosciences, ecology and basin management. Runoff and sediment discharge of river isaffected by climate change and human activities all the time, and the change of runoff andsediment discharge could be attributed to the effect of human activities putting on thesurface material, morphology and process of the paired years with similar weather condition(SWC). In this thesis, the Yellow River basin was chose to be the research area for its severevariation of runoff and sediment discharge. Based on the monthly weather data from1961to2010of94meteorological stations in and around the Yellow River basin, the potentialevaporation (ET0) calculated by Penman-Monteith formula, while the precipitation and ET0were generated with inverse distance weighting spatial interpolation method. The study areadivisions were divided by ArcGIS hydrological analysis model on the basis of5hydrological stations’ catchment area. The paired years were selected out according to thehypothesis of similar values and similar processes and then the change of runoff andsediment discharge between selected paired-years in all the divisions were compared, aswell as the quantities and amplitude of change were calculated. With the combination ofland use and NDVI data, the reason of runoff and sediment discharge change was analyzed.The main conclusions are as follows:1. The paired years with SWC were selected according to2criteria below:(1) thedifferences of yearly precipitation and ET0were small enough (less than2%) as similarvalues;(2) the linear relationship between monthly precipitation and ET0is significantenough (the significant correlation<0.01) as similar processes and the years’ gap is longerthan4years. According to the criteria,12,13,12,4and4SWC paired years were selectedout respectively in the5divisions. All the paired years not just involve plenty of calendardecades in the research period but also the year’s difference within paired-years spanslargely, which make them could reflect the change characteristics of runoff and sedimentdischarge in long periods. Meanwhile, the precipitation of all the paired years also involvesdifferent precipitation conditions. Take the source stream and the third region as examples, paired years of the two divisions both involve from1960s to2010s and cover all thedecades of the study period. Moreover, the years’ gap of the source stream’s paired yearsspans from5to30, while the year’s gap of the third region spans from7to40, in that case,the variation characteristics of the Yellow River basin can be reflected clearly.2. The change of runoff and sediment discharge possess obvious trend. In all theregions, the number of paired years which annual runoff and sediment discharge decline ismore than which increase. For instance, there are11and9paired years show the annualrunoff and sediment discharge decline respectively in all the12paired years of the sourcestream. In13paired years of the second region, there are both7paired years show therunoff and sediment discharge decline respectively. The other regions have the samecondition. The change of the runoff and sediment discharge within the paired years issimilar with their change from1961to2010.3. According to the analysis of land use and NDVI, human activities which effect thechange of runoff and sediment discharge are different in all the regions of the Yellow River.In the upstream area, the dominate reason of the runoff decline is climate and the waterstorage&runoff generation function of the vegetation aggravate the decline of surface flow,whereas the decline of sediment discharge is related to the soil and water conservationfunction’s enhancement of woodland and grassland. In the middle and lower reaches, for thereason of increasing intake and the underlying surface changed by water and soilconservation measurements, the process of flow and sediment producing, confluence haschanged, caused the decline of annual runoff and sediment discharge. In addition, theoperation of water conservancy hub project and dams changed the distribution of runoff inthe time scale, greatly reduced the peak flow and weaken the transportability of sedimentsin flood season.