Analysis On The Causes And Characteristics Of River Runoff Change In Beiyuhe Basin

The Beiyuhe basin,which located in the the extension zone of Qinling Mountains,lies in the intersection zone of the Loess Plateau,Qinba mountainous area and Tibetan Plateau.The complex topography and frequent heavy rains makes the region an area with frequent storm flood and debris flow disaster,which cause huge damage to the local residents.And precipitation,as the only source of water in the region,makes itself and runoff have more direct and closer relationship with the local people's life and production.Under the background trend of global climate change and intense human activities,research on hydrological processes changes in the region is of important significance for hydrological benefit evaluation of ecological construction and implementation the sustainable utilization of regional water resources.Changes in rainfall and vegetation are the key factors affecting regional hydrological characteristics.Based on this,this paper makes use of data from rainfall stations,Majie Hydrologic Station in the Beiyuhe River Basin,and Wudu Weather Station during 1979 to 2014 and land use data from different periods in the study area to macroscopically grasp the annual and interannual variation trend and periodic characteristics of long-term precipitation,temperature,potential evapotranspiration and runoff in Beiyuhe basin,and then capture their turning point year and analyze the change of land use state in different period.The contribution rate of rainfall and other factors(mainly human activities)to annual runoff change was quantitativeiy analyzed by using the double cumulative curve.Based on the HEC-HMS model,the contribution of Land Use / Cover Change and rainfall change to runoff change was analyzed during vegetation restoration period(after 2002).The main conclusions are as follows:(1)The average annual precipitation in the basin during the study period is 495.17 mm,and the overall trend is decreasing.The average annual temperature is 15°C,and the overall trend is an upward trend.Meanwhile,the average potential evapotranspiration is 1024.64 mm,and the overall trend is increasing.The annual average runoff depth is 51.99 mm,and the overall trend shows a downward trend with the declining of 5mm every year.The turning point year of runoff is 1993,the average annual runoff PCD is 0.66 PCD,and the runoff PCP is generally in the middle and early August.In the 1980 s,the land use in the study area was in adjusting period with good vegetation condition.In the 1990 s,land use in the basin was in a period of development with intense human activities.After 2000,land use was again in the adjustment phase in revegetation.(2)Based on DEM and hydrometeorological data,the HEC-HMS model of beiyuhe basin is established to simulate rainfal and rainoff process for rainstom.The accuracy of the model is high,which meets the requirements of the hydrological information prediction standard(SD 138-85).It can be used for subsequent simulation analysis,meanwhile indicating that the HEC-HMS model is suitable for hydrological process simulation and hydrological forecast in this area.(3)By using time series mutation point detection,it is found that there is a mutation in 1993 in the sense of probability,so the whole study period is divided into the baseline period(1979-1993)and the change period(1994-2014).The average annual runoff depth during the change period(1994-2014)relative to the baseline period(1979-1993)was reduced by 51.8 mm.The double cumulative curve method yielded that the contribution of the climate change(rainfall)and other factors(mainly human activities)to annual runoff changes are 19.9% and 80.1%,respectively.(4)For the change period,flood modeling simulation analysis finds that: the contribution rate of rainfall changes has a large difference between runoff depth and peak discharge,and shows a greater impact on runoff depth changes,which are 81.8% and 61.5%,respectively;vegetation changes impact on runoff depth and peak discharges were 18.2% and 38.6%,respectively,which had a significant impact on the flow of flood peaks,and could effectively reduce the peak discharge just as expected.