Study On The Effects Of Climate Change On Ecohyrological Process And Its Interaction Mechanism In The Second Songhua River Basin

Eco-hydrological processes are important for the material and energy balance of land surface,which is closely related to climate.Climate change has altered the spatial and temporal distribution of ecological and water resources,by influencing the physiological and ecological processes of vegetation,as well as the water cycle processes.Northeast China located in the highest-latitude areas,which is the most sensitive to climate change.The eco-hydrological processes in Northeast China have the regional characteristics of cold area,and influenced by climate change evidently,so it is necessarily to research the evolution and response mechanism of eco-hydrological processes under climate change in Northeast China.Through a correct understanding of the response of eco-hydrological processes to climate change,it can be more reasonable to predict runoff and evaporation in the future,and has better serves for the research of agricultural irrigation,ecological restoration and construction,as well as integrated water resources management.In this paper,it takes the Second Songhua River Basin as research region,and assesses the effect of climate change and vegetation variation quantitatively through a method deduced by Fu equation.For the complicated interaction between climate change and eco-hydrological processes,an ecological and hydrological coupling model,Integrated Biosphere Simulator(IBIS)has been established to research the driving mechanism of precipitation intensity,temperature and atmospheric CO2 concentration to the eco-hydrological processes with different scales.The main contents and results are as follows:(1)Mann-Kendall trend test.linear regression method,and five-years sliding average method are used to analysis the variation tendency of meteorological elements and hydrological elements in the Second Songhua River from 1956 to 2010.The precipitation has an insignificant decreased tendency,but the evidently increase of precipitation days has led to a significant decreased of precipitation intensity.And in the past years,temperature has increased significantly.The land use types of research region have inconspicuous change between 1980 and 2014,while the vegetation LAI has an obvious increase during 1980 to 2010.Influenced by the climate change and vegetation,the potential evapotranspiration has been significantly increased.However,the actual evapotranspiration obtained by Remote Sensing shows an insignificant variation,as well as the runoff of the watershed.(2)Based on the observed data,Grey relational analysis and Pearson correlation analysis are used to analyze the relationship between meteorological elements,vegetation elements and hydrological elements.The results indicate that precipitation is the most important for the runoff,temperature and relative humidity affect the runoff by changing evapotranspiration capacity,while temperature and CO2 concentration has indirect effects on the runoff.(3)In order to quantify the contribution of climate change and underlying surface change to runoff variation,a new statistical method was proposed in this paper.Firstly,the parameters of the underlying surface and the runoff equations in different period are proposed by water and heat balance theory.Then the scenarios of different climate and underlying surface change are used to calculate the influences of climate,underlying surface and their synergies on runoff variation.As well as the runoff variation caused by simulation errors.The results show that the contribution of climate change to natural runoff is 64.35%,and the contribution of underlying surface change is 35.65%.To improve the reliability of the quantitative analysis,linear regression analysis method and water and heat balance with univariate analysis were used,the results of which show that the contribution of climate change is 66.05%and 60.77%.Both of the methods show that climate change is the main cause of natural runoff variation in the second Songhua River Basin.(4)The statistical methods could not catch the relationship between vegetation growth and hydrological processes,as well as its response to climate change,so a eco-hydrological model for Northeast China cold regions was established,which based on Integrated Biosphere Simulator.For the regional characteristics of the second Songhua River,as well as the accuracy errors of IBIS model simulations,some improvements were did to modify the model accuracy.Firstly,the substreams were used as the compute cell,which replaced the grid cell.Secondly,the modules of precipitation downscaling,LAI simulation,and snowmelt were modified by the theories of other researches.Thirdly,a confluence processes module was added based on the water cycle theory of Water and Energy transfer Process Model.The comparison of measured values and simulations shown that the modified IBIS model has improved for eco-hydrological process simulation in the Second Songhua River Basin,it can be well used to study the effect of climate change on eco-hydrological processes.(5)The IBIS model was used to simulate the eco-hydrological processes of the second Songhua River basin.The driving effects of climate change on vegetation growth and hydrological processes at different scales,as well as the effects of vegetation growth change on water cycle were analyzed basing on the simulate results.Firstly,by analyzing the response of eco-hydrological elements to climate change,temperature and precipitation has significant influence on water cycle,while the influence of temperature and CO2 concentration on vegetation growth is significant.Secondly,monthly processes of eco-hydrological which is driving by climate change is researched.And the results shows that vegetation LAI has important effect on water cycle and the the driving process of climate change to hydrological process.Under the condition of temperature elevate by 2?,the max LAI will increase from 3.20 to 3.47,and the change of evapotranspiration caused by canopy LAI was 16.82%of the total evapotranspiration variation,which mainly concentrated in May,September and October with large change of LAI.The LAI increase caused the change of runoff variation is 17.20%of the total runoff variation,that mainly concentrated in July to September with large LAI value.As for precipitation,LAI also has an obvious effect,that it influencing the response degree of water cycle to precipitation.Finally,the evolution trend of water cycle is predicted by simulating the eco-hydrological processes in the future with 24 groups climate change scenarios.The results shows that 18 groups' runoff has a decreasing trend,indicating that the water resources in research region probably will reduce in the future,and aggravate the contradiction between water supply and demand.