Moisture transport above the Tibetan Plateau (TP) plays a crucial role in supplying water resources and maintaining the regional moisture budget, particularly in the major mountain ranges that give rise to many of Asia's great rivers. This study examines the sustainability of moisture transport and the mechanisms influencing it in major mountainous regions. The results indicate that moisture transport across the TP has remained relatively stable, with a slight increasing trend in recent decades, suggesting a sustained water supply from the “Asian Water Tower.” The increase in net moisture flux, driven by enhanced moisture inflow at the southern boundary and reduced outflow at the eastern boundary, is the primary cause of the humidification trend over the TP. A key physical mechanism maintaining moisture transport is the coupling between low-level convergence and upper-level divergence, forming a vertical chain of “convergence–condensation–precipitation–divergence.” However, due to differences in topography and moisture content, the altitude and intensity of moisture convergence vary spatially. Over the southern mountains, convergence is stronger and occurs at lower altitudes, leading to a much lower maximum precipitation height compared to the northern mountains, where convergence is weaker and occurs at higher altitudes. Moreover, the convergence layer is shallower in the south than in the north, reflecting spatial differences in the vertical distance over which moisture is converted into precipitation. Despite the relatively stable moisture supply, rapid warming over the southern TP has increased the atmospheric water-holding capacity. However, the significant decrease in atmospheric specific humidity makes it more difficult for the atmosphere to reach saturation, leading to a decline in precipitation in the southern region. Plain language summary Moisture transport is a critical component of the global hydrological cycle and a key factor influencing precipitation generation and variability. This study investigates the spatiotemporal changes in moisture transport over the Tibetan Plateau (TP) to assess the sustainability of moisture supply in this region. From both thermodynamic and dynamic perspectives, we explore the physical mechanisms governing moisture transport. The results indicate that moisture transport over the TP and its mountainous subregions has remained relatively stable, with a slight increasing trend in recent decades. The increase in net moisture flux is identified as the primary driver of increased precipitation over the TP. Influenced by complex topography of the TP, a coupling relationship between low-level moisture convergence and upper-level divergence has developed. This coupling facilitates the continuous transport of moisture onto the plateau and helps maintain the atmospheric moisture supply over the TP. The study further reveals that over the southern mountains, moisture convergence occurs at lower altitudes and with greater intensity, whereas over the northern mountains it occurs at higher altitudes with weaker intensity. This results in a pattern in which the maximum precipitation height over the southern region is much lower than that over the northern mountainous areas. Despite the stable to slightly increasing trend in moisture transport, atmospheric specific humidity has decreased over the southern TP, in contrast to increasing specific humidity in the northwest. Together with rising temperatures that make atmospheric saturation more difficult to achieve in the south, these changes help explain the recent decline in precipitation over the southeastern TP and the concurrent increase in precipitation over the northwestern TP.
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