Variation Analysis Of Hydrologic Elements In Changing Environment

Under the conditions of changing invironment and increasing human activities,the variation occurred in hydrological system caused by climate change and human activities.The hydrological series are the basic of the plan,design,opration and management of water conservancy projects,it must be consistent and representative.However,the variation occurred,it will lead to the assumption of consistency no longer exists.It will affect the security of water conservancy projects which has already completed or will be start,thus,it will the affect the security and development of the country and the nation.Therefore,this study is focus on the hydrology variation problems with the aim is to provide an application scientific basis for Weihe River basin and similar regions.In this paper,according to the hydrology variation problem,we focus on the Weihe River basin.Based on the variation of analysis of streamflow,surface runoff and base flow,respectively,we take the quantitative analysis of climate change and human activities contribution rate of the variation streamflow,surface runoff and baseflow,find the main driving factors.The main results of this study are shown as follows:(1)Comprehensive analysis of the Weihe River runoff variation.By using the Mann-Kendall test to detect the variation point of the precipitation,evaporation,temperature and streamflow,the results show that all the elements occurred the variation.The variation of tributary and main stream runoff of Weihe River has obvious spatial change.The consistencies of the tributary and main streamflow become better along with the flow from upstream to downstream.And it shows that the variation of upstream are weak,the downstream are strong,the tributaries are weak,and the main stream are strong.(2)Quantitative analysis the impact of the inflow of tributaries on streamflow variation.The change of the stream flow of tributary and the variation coefficients are the same.It found that if the contribution rate of streamflow high,the proportional will change significant,but if the proportional are high,not all the contribution rate are high.If the contribution rate of variation coefficient high,the proportional will change significant,but if the proportional are high,not all the contribution rate are high.(3)Analyzed the impacts of the climate change and human activities,and developed the one-parameter Budyko model for Weihe River basin.The results show that the contribution rate of climate change impact on streamflow decreasing at Linjiacun,Xianyang,Lintong and Huaxian 4 hydrology stations of Weihe River basin are 37%,23%,57%and 43%,respectively.Comparison to the climate change,the direct human activities are stronger,and the contribution rate are 63%,77%,43%and 57%,respectively.The direct human activities are the main driving factors of the streamflow decreasing of Weihe River basin.(4)Showed the changing law of the base flow in Weihe River basin,and quantitative analyzed the impact of base flow change on regional water balance.By using Nathan and McMahon base flow split method to calculate the base flow in study area,it shows that the base flow change significantly from 1960-2005 at each stations.It can be found that the if the streamflow will change along with the changing trend,if the total streamflow high,the base flow will be high,however,the surface runoff are changing slightly with stable.(5)Quantitatively analyzed the impacts of climate change and human activities on base flow variation in Weihe River basin.Using the Two-stage annual rainfall participation model at Linjiacun,Xianyang and Huaxian station,the results showed that the contribution of surface runoff and base flow are different.The climate change are the main driving factors of variation change of the surface runoff,with the rate higher than 76%,while the human activities are the main driving factors of the variation change of base flow,with the rate higher than 59%.(6)Under the conditions of hydrological elements variation,it will lead to the assumption of consistency no longer exists.It will the affect the basic of the plan,design,opration and management of water conservancy projects.So,it is the becoming the hot point and key questions in this study area.Firstly,it defines variation points hydrological elements,quantify the abrupt points and variation points and describe its meaning.On the basis of dimensionless dealing of mean values and Cv,it proposed the hydrological variability classification methods.Then it takes systematically analysis of each detecting methods,which include qualitative and quantitative detecting methods.It developed the comprehensive detecting variation system of hydrological,which can be divided into 4 steps:analyzed the reason of the variations;detected the abrupt points;determin the variation classification and comprehensive test.And the last,choosing the streamflow series of Huaxian station in Weihe river basin as an example,which has 51 years long annual streamflow series,to verificate the comprehensive detecting variation system of hydrological.The results indicate that the hydrological elements comprehensive detecting variation is scientific rationality.