The Upper Yellow River Basin (UYRB), located at the junction of the Qinghai-Tibet Plateau, Loess Plateau, and Inner Mongolia Plateau, plays a pivotal role in regional climate dynamics, hydrological processes, and ecological stability, primarily due to its precipitation variability. This study utilizes station-based observational data alongside atmospheric reanalysis data to investigate the interdecadal variability of heavy precipitation during the warm-season from 1980 to 2020 in the UYRB. Furthermore, it provides a comparative assessment of the atmospheric circulation patterns that influenced the observed shifts in heavy precipitation across different periods. The analysis revealed pronounced interdecadal changes in warm-season total precipitation (WSTP), heavy precipitation amount (R90p), and heavy precipitation frequency (R90d) around 2003. Heavy precipitation contributes approximately 40 % to the total precipitation, while changes in heavy precipitation account for up to 81 % of the increased total precipitation in the UYRB, the light precipitation exhibit a negative contribution, and moderate precipitation shows a slight positive contribution. Additionally, the variation in the frequency of heavy precipitation contributes the most, reaching 7 mm/10a, while the intensity of precipitation is only 1.5 mm/10a. After 2003, the frequency of heavy precipitation (R90d) during the warm-season increased by 14.4 %, whereas the intensity of heavy precipitation (R90t) rose by a modest 4.3 %, indicating that the increase in R90d predominantly drives the long-term trend in WSTP over the UYRB. The key factors such as moisture transport, moisture content, instability energy, and vertical motion were compared between two distinct periods: 1980–2002 (Period1) and 2003–2020 (Period2). During P2, there was a marked intensification of anomalous easterly moisture transport and moisture convergence throughout the atmospheric column, resulting in a nearly 50 % increases in net moisture input and a rise of 2.7 % in total columnar moisture content relative to P1. Atmospheric instability exhibited a slight increase, with notable anomalous convergent upward motion detected over the source region of the Yellow River and central Gansu province, likely intensified by orographic effects. A zonally-oriented “+ - +” Silk Road-like teleconnection pattern emerged in the mid-to-upper troposphere over Eurasia since 2003, enhancing westward moisture transport from the Indian Ocean and Pacific. This shift corresponded with increased moisture availability and vertical ascent during the warm-season, which is conducive to a significant increase in heavy precipitation over the UYRB.

中文翻译：

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近 40 年来黄河流域上游暖季强降水的年代际变化及相关大气环流异常


黄河流域上游 （UYRB） 位于青藏高原、黄土高原和内蒙古高原的交界处，主要由于其降水变化，在区域气候动力学、水文过程和生态稳定性中发挥着关键作用。本研究利用基于站点的观测资料和大气再分析资料，研究了 UYRB 1980 年至 2020 年暖季强降水的年代际变化。此外，它还对影响不同时期观测到的强降水变化的大气环流模式进行了比较评估。分析显示，2003 年左右暖季总降水量 （WSTP）、强降水量 （R90p） 和强降水频率 （R90d） 的年代际变化显著。强降水约占总降水量的 40%，而强降水的变化占 UYRB 总降水量增加的 81%，轻降水表现出负贡献，中度降水表现出轻微的正贡献。此外，强降水频率的变化贡献最大，达到 7 mm/10a，而降水强度仅为 1.5 mm/10a。2003 年后，暖季强降水频率 （R90d） 增加了 14.4 %，而强降水强度 （R90t） 略微增加了 4.3 %，这表明 R90d 的增加主要推动了 WSTP 相对于 UYRB 的长期趋势。比较了两个不同时期的水分输送、水分含量、不稳定能和垂直运动等关键因素：1980-2002 年（第 1 期）和 2003-2020 年（第 2 期）。 在 P2 期间，整个大气柱中异常的东风水汽输送和水汽会聚明显加强，导致净水分输入增加近 50%，相对于 P1 总柱状水分含量增加 2.7%。大气不稳定性略有增加，在黄河源区和甘肃省中部地区检测到明显的异常收敛向上运动，地形效应可能加剧了这种运动。自 2003 年以来，欧亚大陆上空的对流层中上游出现了一种以纬向为导向的“+ - +”丝绸之路状遥相关模式，加强了印度洋和太平洋向西输送的水汽。这种变化与暖季期间水分供应的增加和垂直上升相对应，这有利于 UYRB 上强降水的显着增加。