In July and August 2022, a notable “seesaw” extreme pattern emerged, characterized by the “Yangtze River Valley (YRV) drought” juxtaposed with the “Indus Basin (IB) flood”, leading to enormous economic and human losses. We observed that the “seesaw” extreme pattern concurs with the second-strongest sea surface temperature (SST) gradient between the equatorial central and western Pacific caused by the triple-dip La Niña and western Pacific warming. The convergent statistical and numerical evidence suggested that the enhanced SST gradients tend to amplify the western Pacific convection and the descending Rossby responses to the La Niña cooling, promoting the “seesaw” extreme pattern through the westward expansion of the western Pacific subtropical high (WPSH). Further investigation demonstrated that the magnitude of the YRV surface temperature and IB rainfall exhibited a reversed change from July to August. The persistent cooling of the southern Indian Ocean induced by the triple-dip La Niña increases the cross-equatorial moisture transport, which played a significant role in the record-breaking IB rainfall during July. By contrast, the historic YRV surface temperature occurred in August with a decrease in IB rainfall. The Barents-Kara Sea warming extended the downstream impact of the North Atlantic Oscillation via local air-sea interaction that enhanced the WPSH and the YRV extreme surface temperature by emanating an equatorward teleconnection wave train. The overlay of the tropical thermal conditions and extra-tropical forcings largely aggravated the severity of the “YRV drought and IB flood”.

2022年7月和8月，出现了以“长江流域干旱”和“印度河流域洪水”并存为特征的明显“跷跷板”极端格局，导致巨大的经济和人员损失。我们观察到，“跷跷板”极端模式与三重拉尼娜现象和西太平洋变暖引起的赤道中太平洋和西太平洋之间第二强的海面温度（SST）梯度一致。统计和数值证据表明，海温梯度的增强往往会放大西太平洋对流和下降的罗斯比对拉尼娜降温的响应，通过西太平洋副热带高压（WPSH）西扩促进“跷跷板”极端模式。进一步调查发现，7月至8月长江流域地表温度和IB降雨量呈现反向变化。三重拉尼娜现象导致南印度洋持续变冷，增加了跨赤道水汽输送，对7月份破纪录的IB降雨起到了重要作用。相比之下，YRV 地表温度达到历史最高水平是在 8 月份，而 IB 降雨量却有所减少。巴伦支海-喀拉海变暖通过局部海气相互作用扩大了北大西洋涛动的下游影响，通过发出赤道遥相关波列增强了副高和长江流域极端表面温度。热带热力条件和温带强迫的叠加在很大程度上加剧了“长江旱涝”的严重程度。