Decoupling between Horizontal Moisture Transport and Column Water Vapor over the Eastern Slope of the Tibetan Plateau (2000–2024) – The 2022 anomaly and its circulation modulation
Miaomiao Liu¹, Maoshan Li¹*, Xu Ren¹, Yaoming Ma², Fanglin Sun³, and Binbin Wang²
1 Climate Change and Resource Utilization in Complex Terrain Regions Key Laboratory of Sichuan Province, Chengdu Plain Urban Meteorology and Environment Observation and Research Station of Sichuan Province, Sichuan Provincial Engineering Research Center for Meteorological Disaster Prediction and Early Warning, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225, Sichuan, China;
2 State Key Laboratory of Tibetan Plateau Earth System, Environment and Resources, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China
3 State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
* Corresponding author: lims@cuit.edu.cn. Tel: +86 18224456936
Abstract: The eastern slope of the Tibetan Plateau is a steep mountain channel connecting the plateau interior and the Sichuan Basin, where horizontal moisture transport, column water-vapor storage and precipitation conversion may respond differently to climate variability. Based on the NCEP-FNL reanalysis, CMFD precipitation, terrain data and climate indices from 2000–2024, together with FLEXPART backward trajectories, this study examines the decoupling between vertically integrated water-vapor transport (IVT), precipitable water (PW) and precipitation over this topographic transition zone. The annual IVT in 2022 is the lowest of the past 25 years; the summer IVT is the second lowest but there's a positive anomaly for summer PW. The annual and summer IVT decreases significantly during 2000-2024 by -2.586 and -2.979 kg · m⁻¹ · s⁻¹ · a⁻¹, respectively, while PW increases by +0.196 and +0.469 mm · a⁻¹ and annual precipitation shows no significant decline. Wind-humidity decomposition indicates that circulation-related wind changes dominate the IVT decrease, whereas increased humidity partly offsets the weakened transport. High-minus-low IVT composites further suggest that southern and western moisture inflows are the direct transport branches, whereas PNA-related midlatitude variability and the local western-flank WPSH proxy modulate the regional circulation background; ENSO and monsoon indices are treated only as background modulation clues. A simplified summer moisture-budget consistency diagnosis shows that, compared with high-IVT summers, low-IVT summers have weaker moisture convergence (4.98 vs. 10.44 mm · d⁻¹) but higher PW (74.75 vs. 67.53 mm), indicating that reduced horizontal transport mainly weakens large-scale moisture convergence rather than directly determining column water vapor or precipitation. Terrain diagnostics further show that precipitation and low-level moist layers are concentrated over low-to-middle elevation slopes and the plateau-basin transition zone. These results indicate that eastern-slope IVT decline and plateau-wide wetting are not contradictory, because they describe different components of the regional water cycle: horizontal transport efficiency, column moisture storage and precipitation conversion.
Keywords: eastern slope of the Tibetan Plateau; horizontal moisture transport; precipitable water; mountain-channel modulation; FLEXPART trajectory clustering

 

eastern slope of the Tibetan Plateau; horizontal moisture transport; precipitable water; mountain-channel modulation; FLEXPART trajectory clustering