Response Of Runoff To Climate Change And Land Use Change In The Water Source Region Of The South-to-north Water Diversion Middle Route Project

Since the beginning of the Anthropocene,climate change and land use change have shown an accelerated trend,which will inevitably have an important impact on the global water cycle.The South-to-North Water Diversion Project is a key project for the scientific deployment of water resources in China to alleviate the water resource crisis in northern China.The South-to-North Water Diversion Middle Route Project,which spans the Yangtze,Huai,Yellow,and Hai rivers,has transferred water from the Taocha canal head of the Danjiangkou Reservoir since its opening in December 2014,with a current multi-year average of 6 billion m3,and has transferred a total of 36.1 billion m3 of water to northern China.In the context of climate and land use changes,the mechanisms of runoff changes at the project water sources and future water resources trends need to be deeply investigated.In this paper,based on the collection of climate,topography,soil and vegetation data in the study area,the largescale distributed VIC hydrological model and Dinamica EGO model are coupled.Combined with different simulation scenarios designed by scenario backpropagation method,the attribution work of historical runoff changes in the water source region of the South-to-North Water Diversion Middle Route Project is realized.In addition,the future runoff simulation of the study area was constructed by using two climate scenarios(RCP4.5 and RCP8.5)of the downscaled IPCC5 climate model and the future land use data under different scenarios.Based on this,future extreme runoff trends are explored by the range of variability method.The main results are as follows.(1)In the context of the warm-dry trend in the study area during 1979-2018,runoff in the study area decreased by 4.39 m3/s per year,mainly reflected in the decline of runoff during the rainy season.Cross wavelet analysis indicates that precipitation,temperature and potential evapotranspiration have different degrees of influence on runoff in the study area,with precipitation being the main meteorological influence on runoff changes.The sensitivity of runoff to changes in urban and built-up land in the study area was the highest,followed by shrublands,drylands,rice fields and grasslands,and the lowest sensitivity to changes in forested land.(2)The results of the attribution analysis based on the coupled model framework show that climate change is the main driver of runoff changes in the water sources of the South-North Water Transfer Central Project,affecting 99.7%,108.2%,and 102.1% of runoff changes from the 1980 s to 1990 s,1990s-2000 s,and 2000s-2010 s,respectively.In addition,climate change can enhance or attenuate the response of runoff to land use change.(3)Under the economic priority development scenario,the future(2025-2070)multi-year average runoff into the Danjiangkou reservoir increases by 25%-33% compared to the historical period(1979-2018).Under the ecological priority development scenario,the multi-year average runoff into the Danjiangkou reservoir is reduced by 0.38%-6.01%,with the decrease decreasing after 2050 under the RCP4.5 scenario.Although the ecological priority development scenario increases the area of vegetated land in the region,the study area may be exposed to a increased threat of flooding in the future under the influence of larger fluctuations in future rainfall and temperature.This study provides a systematic analysis of the historical climate and runoff patterns in the water source areas of the South-to-North Water Diversion Project,and on this basis,the runoff change mechanism is scientifically investigated,and the results are of great significance for the runoff management of the South-to-North Water Diversion Project and other similar environmental areas.It is worth noting that there is a trend of increasing droughts and floods in the study area in the future.In the context of climate change,a scientific and reasonable scenario configuration for the sensitivity of runoff to land use changes will effectively mitigate the risk of extreme runoff.