The Temporal And Spatial Distribution Characteristics Of Water Vapor Recirculation Rate In The Middle And Lower Reaches Of The Yangtze River And Analysis Of Its Possible Causes

The middle and lower reaches of the Yangtze River is the area of abnormal rainfall in China,so the drought and flood disasters are frequent,and economic,science and technology in this area are developed and densely populated.So the loss caused by drought and flood is even greater.Studying the water vapor recycling rate in the middle and lower reaches of the Yangtze River can simulate the water cycle in the region and understand the hydrological conditions in the region.In this paper,the reanalysis data of NCEP/NCAR is used.Based on the atmospheric water balance equation and Eltahir model,the numerical implementation was designed,and the water vapor recycling rate of the middle and lower reaches of the Yangtze River is calculated.The relationship between water vapor recycling rate and water vapor flux,evaporation and sea surface temperature in the middle and lower reaches of the Yangtze River is analyzed.The results show:(1)The water vapor recycling rate in the middle and lower reaches of the Yangtze River is gradually increasing from southeast to northwest,and gradually increases from 1981 to 2015.The water vapor recycling rate has obvious monthly changes,which are basically unchanged from January to May,the lowest in June,and gradually increase from June to September,and gradually decrease from October to December.The water vapor recycling rate in spring,autumn and winter has increased significantly in the past 35 years.(2)When the study area is selected as a single grid point,the water vapor recycling rate in the middle and lower reaches of the Yangtze River is 0.04 to 0.1,and when the study area is expanded to the middle and lower reaches of the Yangtze River,the water vapor recycling rate is between 0.25 and 0.35.If the study area continues to expand,the water vapor recycling rate will increase.If the study area is global,the water vapor recycling rate will be 1,which means,the water vapor that constitutes the water cycle is all from the local.(3)Water vapor input,evaporation and sea surface temperature are all important factors affecting water vapor recycling rate:Water vapor input,water vapor in the middle and lower reaches of the Yangtze River is mainly input from the southern and western borders.The water vapor source is mainly the Indian Ocean and the South China Sea.The water vapor input is concentrated in the summer,but the total water vapor input decreases slowly from 1981 to 2015.The year of the water vapor input maximum corresponds to the minimum value of the water vapor recycling rate.The evaporation in the middle and lower reaches of the Yangtze River gradually began in 2000.Decrease,and then gradually increase.In addition to local evaporation,the water vapor recycling rate in the middle and lower reaches of the Yangtze River is also related to evaporation in other regions.In summer,it is mainly negatively correlated with evaporation in the Indian Ocean and the South China Sea.In winter,it is mainly negatively correlated with evaporation in the Siberian region.The water vapor recycling rate in the middle and lower reaches of the Yangtze River is mainly related to the pre winter sea surface temperature in the Indian Ocean and the Bay of Bengal.(4)Possible mechanism of water vapor recycling rate affecting the middle and lower reaches of the Yangtze River:The water vapor evaporated from the Indian Ocean,South China Sea and Siberia flows into the middle and lower reaches of the Yangtze River through water vapor,forming the external water vapor in the middle and lower reaches of the Yangtze River.The local evaporation composition comes from Under the joint action of local water vapor and two parts of water vapor,the water vapor in the middle and lower reaches of the Yangtze River changes in circulation rate accordingly.