Analysis the causes of abnormal intensity of the Dragon_boat precipitation in South China

During the Dragon Boat Race around the Dragon Boat Festival every year, it is the period with the highest and most concentrated precipitation during the pre-flood season in South China, and heavy rainfall often leads to serious flood disasters. Analyzing the climate causes of abnormal intensity of the Dragon_boat precipitation in South China in the past 62 years is an urgent need for disaster prevention and reduction. Using daily precipitation data from 192 national meteorological observation stations in South China from 1961 to 2022, a yearly index was constructed to characterize the intensity of the Dragon_boat precipitation in South China. Linear trend analysis, wavelet analysis, and other methods were used to analyze its changing characteristics. Using NCEP/NCAR reanalysis data and SST data, correlation and composite analysis methods were used to analyze the relationship between the intensity anomaly of the Dragon_boat precipitation in South China over the past 62 years and the atmospheric circulation and previous SST anomalies during the same period. The results show that the annual intensity index of Dragon_boat precipitation in South China has obvious interannual and interdecadal changes, and shows an obvious linear upward trend in the past 62 years, shifting from weak before 1993 to strong afterwards. There was mainly an interannual variation cycle of 4-5 years before 1993, there was also an interdecadal cycle of about 16 years in addition to interannual cycles of about 2 and 6 years after 1993. Related analysis shows that during the Dragon_boat precipitation period (May 21-June 20), the geopotential height in the mid latitude region of the North Pacific in the upper troposphere decreases, the southern section of the East Asian trough in the middle troposphere is stronger, the geopotential height in the northern part of South China decreases, and the southern branch trough is stronger. The presence of abnormal anticyclones east of the Philippines in the lower troposphere strengthens the resistance of the Okhotsk Sea on the ground and weakens the high pressure in the Northeast Pacific, which is conducive to the stronger Dragon_boat precipitation in South China. In different interdecadal backgrounds before and after 1993, there were significant differences in the atmospheric circulation between abnormally strong and abnormally weak years during the Dragon_boat precipitation period in South China. After 1993, the divergence over high-altitude in South China became stronger, the water vapor transport from the Western Pacific, South China Sea, and Bay of Bengal to southern China became more prominent, while the cold air from the north to the south was stronger, leading to stronger water vapor convergence and upward movement in southern China, resulting in stronger Dragon_boat precipitation intensity after 1993. Related analysis shows that the tropical Atlantic SST remained low from summer, autumn to winter of the previous year, and the oceanic continental SST was low from summer to autumn of the previous year. The SST in the Northeast Pacific was warm, and SST near the tropical North Pacific Date Line was low in spring of the year, which was conducive to the stronger intensity of the Dragon_boat precipitation in South China. The relationship between the strong and weak years of the Dragon_boat precipitation in South China and SST in the equatorial central and eastern Pacific is asymmetric. The strong years were mainly El Ni?o persistence or attenuation years before 1993, they were mainly La Ni?a persistence or attenuation years after 1993.