Two historic Meiyu events in 1998 and 2020 hit the Yangtze River Valley (YRV), causing catastrophic damage to the socio-economy. By tracking moisture supplies to the extreme precipitation events using Water Accounting Model-2Layers and ERA5 reanalysis, the moisture origins and their differences in feeding the YRV precipitation were revealed. Climatologically, the southwest monsoon channel is the most important moisture channel with the Indian Ocean contributing ∼45% and the Indo-China Peninsula contributing ∼16% of the YRV precipitation. During the two super Meiyu events, the Indian Ocean and the Indo-China Peninsula dominated the excessive moisture supply, which together contributed more than 65% of the extra precipitation. Moisture supply anomalies in 1998 and 2020 showed a robust spatial pattern of “west increase-east decrease”. When the YRV precipitation is higher than the normal, moisture mainly comes from the southwest sources, and moisture contribution from the northwestern Pacific is relatively small. We also found that the intensity of the western Pacific subtropical high is a major influencing factor that explained ∼47% of the YRV precipitation variation during 1991–2020. When it intensifies, an anomalous anticyclone is formed in the mid-lower troposphere around the tropical Northwest Pacific. In its northwestern flank, a strong southwesterly in the upwind of the YRV helps bring in more moisture through the southwest monsoon. In the downwind, it inhibits moisture supply from the northwestern Pacific Ocean. Compared with 2020, a drier condition over Indo-China Peninsula and YRV in 1998 led to a substantially less (∼29%) moisture supply to the YRV precipitation, resulting in a less strong Meiyu event in 1998.

1998年和2020年两次历史性的梅雨事件袭击了长江流域，给社会经济造成了灾难性的破坏。通过使用水核算模型 2 层和 ERA5 再分析跟踪极端降水事件的水分供应，揭示了水分来源及其在供给 YRV 降水方面的差异。从气候角度来看，西南季风通道是最重要的水汽通道，其中印度洋约占长江流域降水量的45%，中南半岛约占长江流域降水量的16%。两次超级梅雨期间，印度洋和中南半岛主导了过量的水汽供给，合计贡献了65%以上的额外降水。 1998年和2020年的水分供给异常呈现出“西增东减”的强烈空间格局。当长江流域降水偏多时，水汽主要来自西南地区，西北太平洋的水汽贡献相对较小。我们还发现，西太平洋副热带高压的强度是解释1991-2020年长江流域降水变化约47%的主要影响因素。当它加强时，在热带西北太平洋周围的对流层中低层形成异常反气旋。在其西北侧，长江逆风中强劲的西南风有助于通过西南季风带来更多的水分。在顺风时，它抑制来自西北太平洋的水分供应。与2020年相比，1998年中南半岛和长江流域气候干燥，导致长江流域降水水汽供应量大幅减少（~29%），导致1998年梅雨事件强度减弱。