Gaoyuan qixiang (Feb 2024)
Analysis of Water Vapor Transport Reduction in the Yarlung Tsangpo Grand Canyon Region: a Trajectory Tracking Approach
Abstract
The Yarlung Tsangpo River Grand Canyon region serves as a main water vapor entrance for the Tibetan plateau.However, the region has been experiencing a persistent decline in both water vapor convergence and precipitation since 1979, which has an important impact on the water storage over the Tibetan Plateau.In order to investigate the reasons behind this reduction in water vapor transport in the area, ERA5 hourly reanalysis data were utilized to drive the LAGRANTO model to derive the backwards water vapor transport trajectories in the region during the boreal summer (June to August) of typical dry and wet years, facilitating a comparative analysis of alterations in moisture flux along these trajectories.It was found that the water vapor sources primarily originating from four oceanic regions: the Bay of Bengal in the southern plateau, the Arabian Sea on the southwest side of the plateau, the Indian Ocean around south of the equator, and the South China Sea.The water vapor transportation in these regions is predominantly governed by the South Asian and Indian summer monsoons and influenced by the Somalia cross-equatorial jet.By comparing the characteristics of water vapor transport trajectories in dry and wet years, it is evident that trajectory patterns remain largely unchanged, with the exception of the South China Sea source.Furthermore, moisture flux along these trajectories diminishes as elevation increases, and the moisture loss during wet years consistently proves to be lower than that during dry years.Additionally, the trajectories originating from the Bay of Bengal source are supplemented by water vapor from the ocean surface, resulting in significant increased water vapor flux in wet years.This finding is supported by comparing the evaporation, precipitation, and circulation fields between dry and wet years.Ultimately, during wet years, the moisture flux reaching the boundaries of the Yarlung Tsangpo Grand Canyon region surpasses that of dry years, notably marked by a particularly significant increase in moisture entering through the southern boundary.This highlights that the depletion processes during water vapor transport, in addition to contributions from moisture sources and the influence of large-scale monsoonal circulation, play a critical role in determining the moisture equilibrium within the Yarlung Tsangpo Grand Canyon region.
Keywords