The 2.8 ka event was a prominent, widespread multicentennial climate anomaly, particularly pronounced across Asia, and has been linked to large-scale reorganization of the East Asian summer monsoon (EASM). Yet, the lack of high-resolution hydroclimate records from southeastern China precludes a definitive understanding of the region's climate response to this event. Here we present a high-resolution, well-dated multiproxy speleothem record (SN33) from Shennong Cave in Jiangxi Province, southeastern China, spanning 3.16 to 2.59 ka BP and fully encompassing the 2.8 ka event. The stalagmite S18O record, interpreted as a proxy for large-scale EASM circulation, exhibits a multicentennial positive excursion with a distinct two-stage structure across the 2.8 ka interval, indicating a pronounced weakening of the monsoon. In contrast, S13C, X/Ca, and initial S234U from the same stalagmite, interpreted as proxies for local hydroclimate, indicate a gradual shift toward wetter conditions in southeastern China during this interval. Comparison of the SN33 multiproxy record with other proxy archives across the EASM domain indicates a highly spatially heterogeneous precipitation response during the 2.8 ka event, with relatively wetter conditions in southeastern China but widespread drying across much of the broader EASM region. Our results further support that the 2.8 ka event likely reflects the combined influence of high-latitude forcing and weakened EASM circulation, while solar variability and internal ocean-atmosphere variability may have modulated the amplitude and spatial expression of hydroclimatic anomalies. The first principal component of SN33 S13C and X/Ca records documents recurrent extreme wet-dry alternations during 3.16-2.59 ka BP that broadly coincide with transformations of the Wucheng and Wannian cultures, suggesting that hydroclimatic variability may have been an important contributing factor shaping cultural trajectories.