Rapid warming over the Tibetan Plateau (TP) has been associated with an increasing trend in atmospheric water vapor content, which is critical for recharging the Asian water tower. However, the mechanism associated with the wetting phenomenon remains unclear. Long-term changes in moisture balance and precipitation (PRE) recycling processes are investigated using the ERA5 reanalysis from 1979 to 2019. The increasing trend over TP is mainly due to the summer water vapor trend with significantly increases over the western TP. Based on the moisture balance analysis, it is found that PRE, evaporation, and the convergence of moisture are all increasing over the western TP but decreasing over the eastern TP. Based on the dynamical PRE recycling model, the results suggest that both internal and external cycles contributes to the wetting over TP, with 63.87% and 36.13% contributions respectively. Further analysis found that the atmospheric heating source is also increasing over the western TP, which could shift the moisture transportation from east to west at the southern boundary of TP. The increasing moisture convergence could enhance PRE, and the enhanced latent heating in the mid-atmosphere can further induced moisture convergence, which forms a positive feedback. However, an opposite situation occurred over the eastern TP. The internal and external cycle of the water cycle can stimulate (suppress) each other through PRE over the western (eastern) TP. This mechanism linked the changes in the PRE recycling and atmospheric circulation, and induced the increasing trend over TP in summer.

中文翻译：

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青藏高原夏季水汽增加的机理

青藏高原（TP）的快速变暖与大气中水汽含量的增加趋势有关，这对给亚洲水塔重新充电至关重要。但是，与润湿现象相关的机理仍不清楚。使用ERA5再分析从1979年至2019年，研究了水分平衡和降水（PRE）回收过程的长期变化。TP的增加趋势主要是由于夏季水汽趋势，而西部TP则显着增加。根据水分平衡分析，发现西部TP的PRE，蒸发和水分会聚都增加，而东部TP则减少。根据动态的PRE回收模型，结果表明内部和外部循环均对TP的润湿有贡献，为63。贡献分别为87％和36.13％。进一步的分析发现，西部TP的大气热源也在增加，这可能会使TP南部边界的水汽输送从东向西转移。越来越多的水分会聚可以增强PRE，中层大气潜热的增强会进一步引起水分会聚，从而形成正反馈。但是，东部TP出现了相反的情况。水循环的内部和外部循环可以通过西部（东部）TP上的PRE相互刺激（抑制）。这种机制将PRE再循环和大气环流的变化联系在一起，并导致夏季TP的增加趋势。进一步的分析发现，西部TP的大气热源也在增加，这可能会使TP南部边界的水汽输送从东向西转移。越来越多的水分会聚可以增强PRE，中层大气潜热的增强会进一步引起水分会聚，从而形成正反馈。但是，东部TP出现了相反的情况。水循环的内部和外部循环可以通过西部（东部）TP上的PRE相互刺激（抑制）。这种机制将PRE再循环和大气环流的变化联系在一起，并导致夏季TP的增加趋势。进一步的分析发现，西部TP的大气热源也在增加，这可能会使TP南部边界的水汽输送从东向西转移。越来越多的水分会聚可以增强PRE，中层大气潜热的增强会进一步引起水分会聚，从而形成正反馈。但是，东部TP出现了相反的情况。水循环的内部和外部循环可以通过西部（东部）TP上的PRE相互刺激（抑制）。这种机制将PRE再循环和大气环流的变化联系在一起，并导致夏季TP的增加趋势。越来越多的水分会聚可以增强PRE，中层大气潜热的增强会进一步引起水分会聚，从而形成正反馈。但是，东部TP出现了相反的情况。水循环的内部和外部循环可以通过西部（东部）TP上的PRE相互刺激（抑制）。这种机制将PRE再循环和大气环流的变化联系在一起，并导致夏季TP的增加趋势。越来越多的水分会聚可以增强PRE，中层大气潜热的增强会进一步引起水分会聚，从而形成正反馈。但是，东部TP出现了相反的情况。水循环的内部和外部循环可以通过西部（东部）TP上的PRE相互刺激（抑制）。这种机制将PRE再循环和大气环流的变化联系在一起，并导致夏季TP的增加趋势。