Response Of Lancang Mekong River Runoff To Climate And Land Use Change

The runoff of Lancang Mekong River Basin has a significant impact on agricultural irrigation,hydropower,fishery and ecology of coastal countries.Predicting the temporal and spatial change of runoff in the future is the basis of Lancang Mekong water resources cooperation.Therefore,this paper studies the watershed runoff change under the joint influence of future climate change and future land use change,simulates the hydrological process of Lancang Mekong River Basin in the future period(2025-2064)by using SWAT model,predicts and analyzes the spatio-temporal change trend of future runoff,quantitatively characterizes the impact of climate change and land use change on hydrological process,and the main research results are as follows:(1)Aiming at the problem of climate model deviation correction,this paper proposes a generalized joint deviation correction method.Based on the frequency correction method of quantile mapping,the correlation of precipitation and temperature elements on the grid scale of meteorological products is evaluated month by month,and the univariate deviation correction or Bivariate Joint deviation correction method is dynamically selected;The dominant effect of meteorological factors on runoff is considered,and the correction order of two variables is dynamically adjusted.The application in Lancang Mekong River Basin shows that considering the correlation between precipitation and temperature can significantly improve the correction effect of precipitation and temperature extreme values,especially in May and June,the Nash coefficient of meteorological and measured data increased by more than 0.5;Considering the correction order of meteorological elements,the frequency distribution and mean deviation of precipitation and temperature after correction are significantly reduced;When the modified meteorological data is used to drive the distributed hydrological model,the runoff simulation accuracy in some months is improved by 54.3%.(2)The generalized joint deviation correction method is used to correct the meteorological data of the basin from 2025 to 2064 output by GCM,and analyze the temporal and spatial evolution law of climate in the future.The results show that the precipitation of each hydrological station in the basin shows a decreasing trend in varying degrees,the decreasing range is less than 10%,and the spatial distribution of rainfall has obvious heterogeneity.The multi-year average temperature in the basin has an increasing trend and the increasing range is1 ～ 3 ℃.(3)IDRISI software is used to build the land use prediction model of the Lancang Mekong basin,and the kappa coefficient of the simulation result is 0.92,indicating that the simulation effect is good.Then,based on this model,the land use situation of the basin in 2035 and 2055 is predicted.The results show that in the land use types of the Lancang Mekong Basin in the future,there is a trend of conversion from grassland to cultivated land,and the conversion rate is between 6% ～ 8%;The water body increased slightly,and the area of forest and construction land did not change significantly.Spatially,the grassland in the upper reaches of Lancang River is the main land type;The agricultural land type in the middle part of the river basin is relatively small,and the main land area remains unchanged;The farmland in the lower reaches is the main land use type,and has a further expansion trend.There is a phenomenon of grassland expansion to forest land in some areas.(4)Considering climate change,land use change and their synergy,this paper sets up ten future combination scenarios to study the temporal and spatial evolution law of future runoff and the effect degree of different environmental factors on runoff.The results show that both climate change and land use change have a reduction effect on runoff,and the synergistic effect of the two enhances the reduction effect,and climate change is the main factor affecting the change of runoff.In terms of time,compared with the reference period,the future runoff of each hydrological station shows a decline in varying degrees,and the annual uneven distribution of runoff intensifies;Spatially,the changes of runoff in the basin show obvious spatial differences,with a large reduction in the upstream and downstream and a small reduction in the midstream.(5)Considering the uncertainty of climate model,this paper uses the data of three climate models gfdl-cm4,miroc6 and mpi-esm1-2-lr to analyze the hydrological temporal and spatial variation characteristics of the Lancang Mekong basin.The results show that in the long term,only the runoff of Qingsheng station,Luang Prabang station,Vientiane station and miroc6 Vientiane station under gfdl-cm4 model will increase slightly,and the future runoff of the other three climate models will still decrease;The spatial variation trend is basically the same.The runoff reduction of Luang Prabang station is the weakest,and the runoff reduction of mudahan station is the largest.