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<p>Since 2000, Southwest China has witnessed a persistent declining trend in spring precipitation, jeopardizing both energy sustainability and downstream ecosystem integrity. However, the underlying moisture transport dynamics for this change remain poorly understood. This study proposed a Lagrangian trajectory model coupled with an objective atmospheric watershed delineation algorithm to identify moisture source regions and quantify their contributions to spring (MAM) precipitation over Southwest China’s Hydropower Bases (SWHB) during 2000–2024. The identified precipitation-source regions were objectively partitioned into five atmospheric watersheds: North (N), Northeast (NE), Southeast (SE), Southwest (SW), and West (W). The SW watershed (Bay of Bengal and northern Indian Ocean) is the primary moisture supplier (&gt; 50%), exerting the dominant impact on spring precipitation variability. The observed precipitation decline is largely explained by reduced water vapor contributions from both the SW and SE watersheds. In addition, the SW contribution has diminished due to reduced water vapor-to-precipitation conversion rates over source regions, whereas the SE watershed suffers from a dual weakening of moisture transport intensity and conversion efficiency. These findings reveal the mechanistic linkage between remote moisture transport anomalies and regional precipitation, providing a physical basis for improving seasonal precipitation prediction and supporting adaptive water-resource management in Southwest China.</p>

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Lagrangian-based analysis of moisture transport anomalies underlying spring precipitation decline in Southwest China’s hydropower bases

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Yang Su,
  • Yinxuan Gao,
  • Jing-Cheng Han,
  • Kaifang Shi,
  • Yuefei Huang

摘要

Since 2000, Southwest China has witnessed a persistent declining trend in spring precipitation, jeopardizing both energy sustainability and downstream ecosystem integrity. However, the underlying moisture transport dynamics for this change remain poorly understood. This study proposed a Lagrangian trajectory model coupled with an objective atmospheric watershed delineation algorithm to identify moisture source regions and quantify their contributions to spring (MAM) precipitation over Southwest China’s Hydropower Bases (SWHB) during 2000–2024. The identified precipitation-source regions were objectively partitioned into five atmospheric watersheds: North (N), Northeast (NE), Southeast (SE), Southwest (SW), and West (W). The SW watershed (Bay of Bengal and northern Indian Ocean) is the primary moisture supplier (> 50%), exerting the dominant impact on spring precipitation variability. The observed precipitation decline is largely explained by reduced water vapor contributions from both the SW and SE watersheds. In addition, the SW contribution has diminished due to reduced water vapor-to-precipitation conversion rates over source regions, whereas the SE watershed suffers from a dual weakening of moisture transport intensity and conversion efficiency. These findings reveal the mechanistic linkage between remote moisture transport anomalies and regional precipitation, providing a physical basis for improving seasonal precipitation prediction and supporting adaptive water-resource management in Southwest China.