Summer Extended Forecast Of The Yangtze River Basin Based On Machine Learning And Possible Contribution Of Soil Temperature And Humidit

The problem of low accuracy of extended-range forecast is an important scientific problem,and it is of great significance to do well in extended-range forecast for disaster prevention and reduction.In this paper,machine learning and deep learning methods were used to carry out the extended-range(5-30 days)forecast experiments of summer precipitation and heat wave in the Yangtze River Basin,and the possible contributions of local surface soil moisture to extendedrange precipitation and local surface soil temperature to extended-range heat wave forecast were discussed.Finally,the possible physical mechanisms of local surface soil moisture affecting extended-range precipitation and local surface soil temperature affecting extendedrange heat wave were preliminarily analyzed.The results show that:(1)The results of machine learning methods in extended-range precipitation forecast are much better than those of traditional linear model methods,and among many machine learning methods,Catboost,Lightgbm and Adaboost are the best;while the results of deep learning methods in extended-range heat wave forecast are better than those of machine learning methods,and CNN,Unet and CNN-TCN are the best.(2)Using the three best machine learning methods,the contribution rate of each forecast factor in the model was calculated.It was found that in the extended period precipitation of the Yangtze River Basin,the local surface soil moisture mainly dominated in 5-10 days,while the early precipitation mainly dominated in 10-15 days,and the extended period precipitation of the Yangtze River Basin was basically controlled by large-scale circulation in 20-30 days.Using the CNN deep learning model to calculate the contribution rate of each forecast factor in the extended period heat wave forecast of the Yangtze River Basin,it was found that the large-scale atmospheric factors dominated in each forecast time,although the local surface soil temperature only occupied a secondary role,its contribution was still not to be ignored.(3)Analysis found that the abnormal evaporation caused by the abnormal surface soil moisture and surface temperature in the Yangtze River Basin will further cause abnormal surface temperature,resulting in abnormal sensible heat,which can cause abnormal atmospheric circulation and vertical motion,and eventually affect summer precipitation;while the abnormal surface longwave radiation caused by the abnormal surface soil temperature in the Yangtze River Basin can cause 2-meter air temperature abnormality.This study provides a certain reference for extended period precipitation and heat wave prediction and exploration of forecast factor contribution rate.