Abstract Two record-breaking summer droughts hit Southwest China (SWC) in 2006 and 2011, causing severe losses to the society and economy. Moisture sources for precipitation in SWC and changes accompanied with the extreme droughts are thus investigated using a moisture tracking model, the Water Accounting Model-2layers (WAM-2layers), with observation-constrained data. SWC is influenced by three major circulations, namely, the Indian monsoon, the East Asian summer monsoon (EASM), and the westerlies. The representative source regions, the Southwest, Southeast, and West, contribute around 50.8 ± 3.9, 13.3 ± 3.8, and 16.4 ± 2.1% of the tracked moisture climatologically. The westerlies turn out to be the second-largest moisture contributor to SWC over the EASM. In 2006 when the western Pacific subtropical high (WPSH) intruded to the west, the influence of the EASM was intensified profoundly as it increased to be the second largest contributor to contribute 21.2% of the moisture. But this change induced circulation anomalies that hindered moisture transport from the West and Southwest. Their moisture contributions were substantially reduced, resulting in an overall moisture deficit for SWC. In 2011, the contributions from subregions were universally reduced. The moisture conveyor belt in the Southwest released moisture early before it reached SWC, thus resulting in a shortage in moisture supply to SWC. The precipitation recycling ratio in SWC is around 15.7 ± 1.9%. However, the ratio increased during both droughts to 18.6% in 2006 and 17.7% in 2011. Further analyses reveal that the external moisture decreased heavily, thus making local moisture more important to result in a marked increase in the recycling ratio.

中文翻译：

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西南地区夏季降水水分来源及2006年和2011年极端干旱期间的变化

摘要 2006年和2011年两次破纪录的夏季干旱袭击了西南地区，给社会和经济造成了严重损失。因此，使用水分跟踪模型、水核算模型-2 层 (WAM-2layers) 和观测约束数据来研究 SWC 降水的水分来源和伴随极端干旱的变化。SWC 受三个主要环流的影响，即印度季风、东亚夏季风 (EASM) 和西风。代表性的源区，西南、东南和西部，在气候学上贡献了大约 50.8 ± 3.9、13.3 ± 3.8 和 16.4 ± 2.1% 的跟踪水分。结果证明，西风带是 EASM 上 SWC 的第二大水分贡献者。2006年西太平洋副热带高压（WPSH）向西侵入时，EASM 的影响显着增强，因为它成为第二大贡献者，贡献了 21.2% 的水分。但这种变化导致环流异常，阻碍了来自西部和西南的水分输送。它们的水分贡献大大减少，导致 SWC 的整体水分不足。2011年，次区域捐款普遍减少。西南地区的水分输送带在到达SWC之前提前释放水分，导致SWC的水分供应不足。SWC 的降水再循环率约为 15.7 ± 1.9%。然而，在两次干旱期间，这一比例都增加到 2006 年的 18.6% 和 2011 年的 17.7%。进一步分析表明，外部水分大幅减少，