Study On Land-atmosphere Coupling Short-term Runoff Forecast In The Upper Reaches Of The Yangtze River

There are abundant water resources in the upper reaches of the Yangtze River.How to transfer them reasonably and efficiently has always been a major problem for the country.Moreover,in recent years,under the dual influence of climate change and large-scale water conservancy project construction,the hydrological change process of the basin has been changed,which requires us to fully grasp the current hydrological cycle process of the basin,so as to scientifically guide the rational allocation of water resources and the safe and economic operation of hydropower energy system.Taking the upper reaches of the Yangtze River as the main research object,this paper analyzes the evolution characteristics of hydrological and meteorological factors in the river basin,studies the methods of rainfall forecast in the river basin,and explores the technologies and methods to improve the accuracy of land-atmosphere coupling model.The achievements include the following aspects:(1)In order to study the trend rule and evolution characteristics of hydrometeorological elements,the rainfall and runoff changes in the basin were analyzed by Mann Kendall test,sliding t test and wavelet analysis.The results show that the annual rainfall and runoff in the Pingshan-Yichang interval in the upper reaches of the Yangtze River generally show a decreasing trend,and the catastrophic years are mainly concentrated in 1984,1993,1997,2001 and other years,indicating that the water regime information of the watershed after 2000 is basically consistent and In the future,rainfall and runoff will continue to decrease.(2)In order to improve the accuracy of rainfall forecast in the basin,different microphysical processes,boundary layer and cumulus convective parameterization schemes in WRF model are studied.Each scheme is evaluated by TS score,mean absolute error and Blair score,and the AR model is introduced to correct the rainfall forecast results.The results show that when the optimal parameterized combination scheme is WRF single moment 3-class scheme,Yonsei University scheme and new Kain Fritsch scheme,the rainfall simulation accuracy of WRF model is the highest;the corrected rainfall forecast can partially correct the phenomenon of "peak staggering",and the simulation accuracy is better.(3)In order to study the future water regime changes in the upper reaches of the Yangtze River and explore the technology of land-atmosphere coupling runoff prediction model,a top-down runoff prediction system of the basin is constructed based on the historical rainfall data;on this basis,the rainfall prediction results before and after correction are introduced,and then the land air coupling prediction system of the basin is established.The results show that the model accuracy of each section is class A,which can be used for the operation forecast of the upper reaches of the Yangtze River;secondly,the land-atmosphere coupling model after rainfall correction is better than the land air coupling model before rainfall correction,and its practical effect in Zhutuo and Three Gorges section is obvious,which can improve the forecast accuracy in a certain degree.