Zhao et al. (2025) Upstream evaporative moisture sources anchor strong persistent heavy precipitation events over southeastern Tibetan plateau

Identification

• Journal: Climate Dynamics
• Year: 2025
• Date: 2025-12-19
• Authors: Ruiyu Zhao, Bin Chen, Wei Zhang, Yeran Yu, Juan Huo, Xiangde Xu
• DOI: 10.1007/s00382-025-07995-z

Research Groups

• State Key Laboratory of Severe Weather Meteorological Science and Technology (LaSW), Chinese Academy of Meteorological Sciences (CAMS), Beijing, China
• Utah State University, Logan, UT, USA
• Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Short Summary

This study investigates the physical mechanisms behind the intensity variations of persistent heavy precipitation events (PHPs) over the Southeastern Tibetan Plateau (SETP) by analyzing upstream evaporative moisture uptakes (UEMU) anomalies using Lagrangian modeling. It reveals that strong PHPs are primarily fueled by enhanced evaporative vapor from remote oceanic regions, while weak PHPs rely more on local recycling, emphasizing the dominant role of large-scale atmospheric circulation patterns in modulating PHP intensity.

Objective

• To identify the spatial and temporal characteristics of upstream evaporative moisture uptakes (UEMU) associated with persistent heavy precipitation events (PHPs) over the Southeastern Tibetan Plateau (SETP), comparing them to the climate mean state.
• To quantify the extent to which the variability in these UEMU is connected to variations in PHP intensity.

Study Configuration

• Spatial Scale: The target area (SETP) is defined as 29.8°N to 31.5°N and 102.6°E to 104.5°E. The Lagrangian model (FLEXPART) simulation domain covers 0–60°N and 0–160°E. Gridded observation data (CN05.1) and reanalysis data (ERA5) have a resolution of 0.25° × 0.25° longitude-latitude, while ERA-Interim has 0.75°×0.75° longitude-latitude. UEMU fields are linearly interpolated to 1.0°×1.0° grids.
• Temporal Scale: The study period for precipitation records and Lagrangian modeling outputs is 1980–2021, focusing on boreal summers (June, July, August). Lagrangian simulations track air parcels from April 15 to September 15 each year, with air parcel selection for UEMU from May 1 to August 31. Data from reanalysis and model outputs are at 6-hour intervals. Backward trajectories are tracked for 10 days.

Methodology and Data

• Models used:
  • Lagrangian transport and dispersion model: FLEXPART (V9.02) for multiyear ensemble simulations to identify moisture sources.
  • Self-Organizing Map (SOM) clustering (using cost733class software) to categorize PHPs based on moisture source data.
• Data sources:
  • Daily precipitation records: From 2,400 gauge sites across mainland China (1980–2021) and 26 gauge stations in the SETP from the National Meteorological Information Center (NMIC) of the China Meteorological Administration.
  • Gridded observation dataset: NMIC’s 0.25° × 0.25° CN05.1 for detailed precipitation spatial distribution.
  • Atmospheric reanalysis datasets:
    • ERA5 (Hersbach et al., 2020) for atmospheric variables (geopotential height, potential vortices, air temperature, three-dimensional wind speed, specific humidity, column-integrated water vapor flux, and divergence) at 0.25° × 0.25° resolution and 6-hour intervals, with 1000 hPa to 1 hPa vertical levels.
    • ERA-Interim (Dee et al., 2011) for driving the Lagrangian model, at 0.75°×0.75° resolution and 6-hour intervals, with 60 hybrid model levels from the surface to 0.1 hPa.

Main Results

• Climatologically, upstream evaporative moisture uptakes (UEMU) for PHPs over SETP exhibit a southwest-northeast distribution, with local recycling and Indian/East Asian summer monsoons as dominant moisture suppliers. The SETP and surrounding areas are the strongest contributors.
• UEMU anomalies during PHPs show a northwest-southeast dipole pattern, with positive values concentrated over Southeast Asia (SEA), South China Sea (SCS), Bay of Bengal (BOB), and Arabian Sea (AS), and negative values to the northeast. SEA is the primary center of positive UEMU anomalies.
• During PHPs, the combined contribution of UEMU from SEA, BOB, and SCS significantly increases to 56.44%, which is 28.5% higher than the climatic mean.
• Temporal evolution of UEMU anomalies reveals that short-term (1-day) transport shows negative anomalies (local convergence), while 2-day transport shows enhanced UEMU southeast of SETP. For longer transport times (7–10 days), positive UEMU anomalies shift to low-latitude oceanic regions (SCS, BOB, AS).
• PHPs are categorized into two types: T1 (weak, average 56.06 mm per event) and T2 (strong, average 80.65 mm per event).
• Strong PHPs (T2) are characterized by more enhanced evaporative vapor from remote lower-latitudinal regions (e.g., Indian Peninsula, AS) with 7–10 day transport times. Weak PHPs (T1) show a decreased contribution from the SETP itself and SEA at short-term (1–3 days) transport scales. This indicates that remote moisture sources are crucial for strong PHPs, while local recycling is more prominent for weak ones.
• Large-scale atmospheric circulation patterns for both PHP types include a stronger South Asian High, a pronounced westerly jet, and a wave train between 40°N and 60°N at 500 hPa. However, strong PHPs (T2) are associated with a more significant anomalous wave train and a northward extension of the Western Pacific Subtropical High (WPSH) at 500 hPa.
• At 700 hPa, T1 is linked to a cyclonic anomaly over the Indian Peninsula and tropical SCS, with easterly wind anomalies hindering moisture transport. T2 shows a less noticeable cyclonic anomaly and an anticyclonic anomaly over Eastern China (related to WPSH), which enhances southeastward wind anomalies and facilitates moisture import from SEA, BOB, AS, and Indian Oceanic regions.
• Local atmospheric transport for T2 (strong PHPs) exhibits greater water vapor flux and more intense upward movement around the SETP compared to T1, with stronger westward and northward wet advection.

Contributions

• This study establishes "upstream evaporative moisture uptake regions" as key anchors for persistent heavy precipitation events, offering a source-to-sink perspective for understanding precipitation extremes over the Tibetan Plateau.
• It enhances the quantifiability of mechanistic research by linking downstream extreme weather predictors to upstream land-surface processes.

Funding

• National Key R&D Program of China (2023YFC3010700)
• China National Natural Science Foundation (Grant number 42475010)
• Major Science and Technology Project of the Xizang Autonomous Region (XZ202402ZD0002)
• S&T Development Fund of CAMS (2021KJ021; 2023KJ027)

Citation

@article{Zhao2025Upstream,
  author = {Zhao, Ruiyu and Chen, Bin and Zhang, Wei and Yu, Yeran and Huo, Juan and Xu, Xiangde},
  title = {Upstream evaporative moisture sources anchor strong persistent heavy precipitation events over southeastern Tibetan plateau},
  journal = {Climate Dynamics},
  year = {2025},
  doi = {10.1007/s00382-025-07995-z},
  url = {https://doi.org/10.1007/s00382-025-07995-z}
}