El Niño modulated Holocene hydroclimate extremes as a dipolar pattern of droughts in northeastern China and floods in southwestern China

Holocene weak Indian summer monsoon (ISM) precipitation has been linked to increased El Niño occurrence on centennial timescales. However, historical data document episodes of extreme precipitation in ISM-dominated southwestern China during El Niño summers. To resolve this discrepancy and better understand the spatiotemporal patterns of El Niño–Southern Oscillation (ENSO)-related climate extremes, we present a 12,000-yr high-resolution reconstruction of floods and monsoon precipitation from Yangzong Lake in southwestern China, based on grain-size and elemental proxies. By comparing this record with other paleoclimatic archives across the Asian monsoon region, we identify a trend of increasing floods superimposed on a long-term decline in Holocene monsoon precipitation. This pattern coincides with a hydroclimatic seesaw: floods in the ISM-dominated southwest and droughts in the East-Asian-summer-monsoon-dominated northeast, correlating with an increase in El Niño events. Previous studies using modern observations and numerical simulations indicate that under El Niño conditions, the strengthened and southwestward-shifted West Pacific subtropical high blocks northeastward moisture transport from the Bay of Bengal, concentrating rainfall over southwestern China, while simultaneously impeding northward moisture flow from the western tropical Pacific, leading to droughts in northeastern China. This mechanism is supported by the shared harmonic quasi-periodicities between these extreme climate events and ENSO activity.