Simulation And Prediction Of Blue-green Water In The Weihe River Basin Under Land Use And Climate Change

The Wei River Basin is an important birthplace of Chinese farming culture and one of the major barriers to food production security in China.Blue water is a directly accessible freshwater resource for human life and production,while green water nourishes rain-fed agriculture and provides great support for food production security.Studying the temporal and spatial characteristics of blue and green water under land use change and climate change in this basin provides clear ideas for water resource allocation and recycling in the Yellow River Basin,which is conducive to strengthening ecological protection and promoting high-quality development in the Yellow River Basin.Based on the SWAT hydrological model,we simulated the blue and green water in the Weihe River basin under land use and climate change and predicted the future blue and green water in the basin.Firstly,we set up different scenarios by fixing other factors and changing only climate or land use and quantitatively analysed the effects of land use change,climate change,and combined changes of both on the changes of blue water,green water,and green water coefficients in the Weihe River basin.Markov model and SDSM model to predict the future land use and climate of the Weihe River basin;finally,the future land use and climate data were input into the SWAT model to simulate the future blue and green water production and spatial distribution of the Weihe River basin.The main research contents and conclusions are as follows:(1)Annual runoff data from 1979 to 2018 were analysed for abrupt changes at the hydrological stations of Shou Tou,Zhangjiashan,Huaxian,Linjiacun,and Xianyang in the Weihe River basin using the cumulative distance level method and the sliding t-test method,respectively,and the study found that abrupt changes in runoff occurred in1993.A SWAT model was developed using elevation data,soil classification data,land use data,and meteorological data in the study area,and the model results were ratified and validated using the SUFI-2 algorithm based on monthly runoff data from 1981 to1992.This indicates that the SWAT model has good applicability to the Weihe River basin.(2)Using CA-Markov as the future land use prediction model,we established analytical relationships through coupled metacellular automata and Markov chains based on the land use base data of 1990 and 2000,and simulated the 2010 land use map of the basin.The kappa coefficient between the simulated land use type map in 2010 and the measured land use type map in 2010 was 0.86,indicating a good simulation effect,which indicates that the CA-Markov model has high reliability and applicability in predicting the future land use in the Weihe River basin.(3)Can ESM5,MPI-ESM1-2-HR,and Nor ESM2-MM were input into the calibrated SDSM model,and the filtered forecast factors were used to predict future climate data from each of the three models.The temperature and precipitation of Can ESM5,MPI-ESM1-2-HR,Nor ESM2-MM,and MME models(the average model ensemble of Can ESM5,MPI-ESM1-2-HR,and Nor ESM2-MM models)were analysed with Taylor diagrams,and the results indicated that the simulation effect of the MME model was closest to the measured values.Using MME as a model to predict the future climate of the Weihe River basin,precipitation and temperature in the basin show an increasing trend under the three emission scenarios,and the magnitude of the increasing trend is SSP5-5.8>SSP2-4.5>SSP1-2.6.(4)Climate change contributes 94%,86%,and 54% to the changes of blue water,green water,and green water coefficients in the Weihe River basin,and land use contributes 6%,14%,and 46% to the changes,so the changes of blue water,green water,and green water coefficients in the Weihe River basin are mainly driven by climate change.The Weihe River basin will have more blue water,more green water,and lower green water coefficients in the future.The future spatial distribution of blue water is more north than south,more east than west,and less in the middle;the future spatial distribution of green water is abundant in the southeast and scarce in the northwest;and the future spatial distribution of green water coefficient is high in the north and low in the south.