Title: Monthly Distribution Characteristics of Medium and Small Floods in Upper Reaches of the Yangtze River and Their Weather Causes
Abstract: Based on the daily mean flow of Yichang station,precipitation of 287 weather stations in the upper reaches of the Yangtze River and NCEP reanalysis data with 2. 5° × 2. 5° spatial resolution from 1981 to 2012,128 medium and small flood processes in the upper reaches of the Yangtze River were selected according to the defined criteria,then the monthly distribution characteristics of floods and flood- causing precipitation processes and their weather causes were analyzed. The results indicated that the medium and small floods in the upper reaches of the Yangtze River mostly occurred in July to September,the duration got gradually longer from June to September,and the maximum duration of discharge occurred in July,while the maximum peak of discharge and flood volume appeared in August. In June,the location of subtropical high and South Asia high were to the east and south compared with the normal,the cold air moving southward under Baikal lake trough guidance converged with the southwest jet over Chongqing- Yichang and Wujiang basins,which caused the uneven distribution of rainfall in sub- basins,the center position of rainfall was to the east,heavy rainfall days were fewer but intensity was larger. In July,the subtropical high and South Asia high were to the west and north,many short wave troughs appeared in the mid- high latitude,southwest warm airflow was strong,convergence zone was wide,which resulted in wide precipitation range and uniform distribution,and more strong precipitation days. In August,the subtropical high was moving further to the west and north,circulation in mid- high latitude was straight,convergence center was located in the northwest of the upper reaches of the Yangtze River,coordinating with high heat and high humidity environment field,which was easy to cause local heavy precipitation,the center of rainfall was located in Min- Tuojiang basin and the area precipitation was larger. After September,with the subtropical high moving to westward and South Asia high moving to southeastward,the surface cold air was very active and stronger owing to influence of deep northeast trough. Combined with weak southwest warm and wet airflow,the precipitation intensity weakened,area precipitation was small,and the center of rainfall was located in Min- Tuojiang and Jialingjiang basins.
Publication Year: 2015
Publication Date: 2015-01-01
Language: en
Type: article
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