Study On Rainfall Runoff Forecast Based On Land-atmosphere Coupling In The Upper Reaches Of The Yangtze River

The Yangtze River Basin have played an important and strategic role in China's social and economic sustainable development,and the upper reaches of the Yangtze River concentrate most of the water resources,which is the key watershed for comprehensive planning,design,development and utilization of hydropower resources in China.Under the influence of human activities,global climate change and the construction of large-scale water conservancy projects,the natural evolution law of water resources system has been seriously damaged.Fully grasping the water cycle process in changing circumstances provides an important reference for the planning and construction of water conservancy projects,optimal allocation of water resources,and safe and economic operation of hydropower systems.In this paper,we focus on the evolution law of natural water circulation process and the scientific problems faced in the process of rainfall runoff prediction in changing environment.We analyzed the temporal and spatial evolution situation of meteorological and hydrological elements,explored advanced theories and methods to improve the accuracy of precipitation prediction,and studied the key technologies and methods to increase the forecast period of short-term runoff in the upper reaches of the Yangtze River.The main research contents and achievements of this paper include the following aspects:(1)This study analyzed the temporal and spatial evolution characteristics of hydrometeorological elements of the upper Yangtze River basin.We studied evolution trend,catastrophic characteristics,periodic characteristics of hydrometeorological elements and meteorological drought evolution in the basin using Mann-Kendall trend analysis,cumulative anomaly,wavelet analysis method and standard precipitation transpiration index.The results show that rainfall and runoff increase in the flood season,rainfall and runoff decrease in the dry season,the annual average rainfall and runoff decrease in an insignificant manner,and the temperature shows a significant upward trend,it is in a trend of drought in basin.It revealed that the frequency of drought or flood hydrological disasters will increase in the future.(2)In order to improve the accuracy of rainfall forecasting and increase the forecasting period effectively in the upper reaches of the Yangtze River,the combination of parameterized schemes suitable for the physical process of the river basin was optimized.According to the geomorphological and geological characteristics of the basin and the climate change conditions,we established the combination of different cloud microphysical processes,land surface processes and cumulus parameterization schemes in WRF model.We constructed a multi-index comprehensive evaluation system including mean absolute error,Blair score,TS score and qualified rate.Based on TOPSIS multi-attribute decision making,we proposed an optimal parameterization scheme selection method.The study shows that when selecting the WSM3 scheme,Noah scheme and the KF scheme,the simulation accuracy is the highest in the upper reaches of the Yangtze River,indicating the necessity of selecting suitable parameterization schemes for different areas,and it has broad application prospects.(3)In view of the applicability of different numerical model forecasting products in the study area,the problems of how to increase the forecast period of runoff effectively in the process of short-term runoff forecasting has solved.The performance of precipitation forecasting products issued by T639 and Ecmwf model in the upper reaches of the Yangtze River is evaluated respectively from the basin surface rainfall process and the basin rainfall spatial distribution process.Based on the measured meteorological and hydrological data in the basin,we established a short-term runoff forecasting system in the upper reaches of the Yangtze River.On this basis,we established the land-air coupling system for short-term runoff forecasting of the watershed with a coupled numerical weather forecasting model.The results showed that the T639 and Ecmwf models,which forecasted the trend of rainfall distribution,and the location of the rainfall center was close to that of the real rainfall,but the forecast rainfall was slightly larger in the 24 to 168 hours.The accuracy of prediction of land-atmosphere coupling system in the upper reaches of the Yangtze River was high,which can increase the forecast period of runoff forecast effectively.Cuntan's runoff forecasting is the best,and the accuracy of runoff forecasting in the 7-day forecasting period reaches Class A standard.It had high practical value and was great practical value in reducing hydrological disasters in watersheds,providing an important reference for water resources planning.