Abstract: Using daily precipitation data from 86 national meteorological observation stations in Guangdong from 1961 to 2024, NCEP/NCAR reanalysis data, NOAA"s ERSSTv5 sea surface temperature (SST) data, and monthly outgoing longwave radiation (OLR) data, the short-term drought-flood abrupt alternation index (SDFAI) for Guangdong was first calculated to analyze the characteristics of drought-flood abrupt alternation in Guangdong over the past 64 years. Then, composite and correlation analysis methods were employed to examine the characteristics of concurrent atmospheric circulation anomalies and preceding sea surface temperature anomalies associated with the SDFAI anomalies in Guangdong, focusing on the period from March to April, when the probability and intensity of drought-flood abrupt alternation are highest and strongest over the past 64 years. The results show that over the past 64 years, the highest probability and intensity of short-term drought-flood abrupt alternation between two consecutive months in Guangdong occurred in March–April, while the lowest occurred in January–February. The SDFAI for March–April exhibited significant interannual and interdecadal variability over the past 64 years, with the highest value in 1973 (3.43) and the lowest in 1968 (-2.49). Approximately one-quarter of the years experienced drought-flood abrupt alternation during March–April. Over the past 64 years, the index showed a significant decreasing trend at a rate of 0.15 per decade. The index was relatively high during 1961–1990 and relatively low during 1991–2024.After detrending the SDFAI, high-index years and low-index years for drought-flood abrupt alternation in March–April over the past 64 years were selected. Composite analyses of atmospheric circulation for these two groups revealed significant differences. During the drought period in March in high-index years compared to low-index years, convergence in the upper troposphere strengthened, the East Asian trough in the mid-troposphere intensified, cold air activity was stronger, and anomalous northerly flows prevailed over South China in the lower troposphere. At the surface, both the Siberian High and the Aleutian Low were significantly stronger. Subsidence motion was pronounced over Guangdong, and low-level divergence dominated over South China. Moisture transport from the Bay of Bengal, the South China Sea to South China weakened, resulting in significantly reduced precipitation in Guangdong in March. During the flood period in April, the characteristics of atmospheric circulation were almost opposite to those in March, leading to anomalously high precipitation in Apr.In the preceding winter, higher SSTs in the tropical western Pacific, lower SSTs in the South China Sea, the western side of the Maritime Continent, and the northern Indian Ocean, along with lower SSTs in the equatorial central and eastern Pacific during the preceding autumn and winter (indicating a decaying or persistent La Ni?a event), strengthened the Walker Circulation. An anomalous cyclonic circulation formed near the Philippines, placing South China under the influence of anomalous northerly flows and within a subsidence region, which contributed to reduced precipitation in March. In April, the rise in SSTs in the tropical western Indian Ocean favored moisture transport from the Arabian Sea and the Bay of Bengal to South China. The increase in SST in the tropical western Pacific helped maintain the anomalous anticyclonic circulation east of the Philippines, strengthening the western Pacific subtropical high. South China was under ascending motion, with convergence of cold and warm airflows in the lower troposphere, enhanced convection and convergence, leading to anomalously high precipitation in Guangdong in April and the occurrence of drought-flood abrupt alternation.