Liu et al. (2026) Mechanisms of two types of summer persistent extreme precipitation events in the northeastern Tibetan Plateau

Identification

• Journal: Weather and Climate Extremes
• Year: 2026
• Date: 2026-01-07
• Authors: Qiaohua Liu, Lun Li
• DOI: 10.1016/j.wace.2026.100853

Research Groups

• State Key Laboratory of Severe Weather Meteorological Science and Technology, Chinese Academy of Meteorological Sciences, Beijing, China
• Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province, Institute of Tibetan Plateau Meteorology, China Meteorological Administration, Chengdu, China
• Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science and Technology, Nanjing, China

Short Summary

This study investigates the characteristics and underlying mechanisms of two distinct types of summer persistent extreme precipitation events (PEPEs) in the northeastern Tibetan Plateau, revealing that Type1 is thermally triggered by latent heating in warm, moist environments, while Type2 is dynamically forced by an eastward-moving quasi-barotropic cold trough in cold, dry environments.

Objective

• To investigate the characteristics and underlying mechanisms of persistent extreme precipitation events (PEPEs) over the northeastern Tibetan Plateau from a synoptic perspective, by objectively classifying PEPEs into distinct types.

Study Configuration

• Spatial Scale: Northeastern Tibetan Plateau (33°–39°N, 97°–104°E).
• Temporal Scale: Summer (June–August) of 2005–2021.

Methodology and Data

• Models used: Self-Organizing Map (SOM) for circulation classification; Ertel Potential Vorticity (PV) equation and PV tendency equation for budget diagnosis.
• Data sources: Hourly rain gauge data from 42 national meteorological stations (National Meteorological Information Center, China Meteorological Administration); European Center for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) datasets (1-hour temporal resolution, 0.25° × 0.25° spatial resolution, 37 vertical levels).

Main Results

• Persistent extreme precipitation events (PEPEs) in the northeastern Tibetan Plateau are classified into two types: Type1 (thermally triggered, 52.94% of events) and Type2 (dynamically forced, 47.06% of events).
• Type1 (Thermally Triggered):
  • Average duration: 20.8 hours (maximum 39 hours).
  • Rapid development (approximately 5 hours to peak), followed by slow weakening (approximately 11 hours to end).
  • Wider spatial coverage with an average accumulated precipitation of 0.01102 meters.
  • Develops in anomalously warm and moist environments across the Tibetan Plateau, accompanied by a localized quasi-stationary shallow trough.
  • Convection is initiated by thermodynamic forcing, where latent heating dominantly increases potential vorticity (PV) in the mid-lower troposphere, enhancing the trough and precipitation.
  • PV increase is characterized as an "ignite-then-fuel" process, with latent heat release (internal fuel) driving PV growth in the mid-lower troposphere, assisted by upper-level PV advection (external fuel).
• Type2 (Dynamically Forced):
  • Average duration: 18.6 hours.
  • Relatively steady and symmetrical evolution (approximately 8 hours to peak, 8 hours to end).
  • More concentrated spatial distribution, mainly affecting the northern part of the study region, with an average accumulated precipitation of 0.00910 meters.
  • Closely associated with a quasi-barotropic cold trough in mid-high latitudes, developing in an overall anomalously cold and dry environment over the Tibetan Plateau, with moisture concentrated in the northeast.
  • Precipitation is triggered by intense dynamical forcing east of the trough.
  • As the trough moves eastward, the intrusion of high-PV air from the upper troposphere enhances the cold trough through horizontal and vertical advection.
  • PV increase is dominated by PV advection from the quasi-barotropic cold trough ("dynamic engine"), with diabatic heating playing a weak supporting role.
• For both types, precipitation shows a coherent temporal evolution with relative vorticity and PV; the PV tendency at 500 hPa shifts from negative to positive approximately 3 hours before precipitation starts, providing favorable conditions for subsequent PV intensification.

Contributions

• Provides a comprehensive understanding of the characteristics and underlying mechanisms of persistent extreme precipitation events (PEPEs) in the northeastern Tibetan Plateau by objectively classifying them into two distinct types.
• Advances theoretical insights into the formation and evolution mechanisms of PEPEs, highlighting the dominant roles of thermodynamic triggering (Type1) versus dynamical forcing (Type2).
• Offers valuable guidance for operational weather forecasting and disaster prevention efforts in the Tibetan Plateau and its downstream regions.

Funding

• Major Science & Technology Special Projects of Tibet Autonomous Region (XZ202402ZD0006-03)
• National Key Research and Development Program (Grant No. 2023YFC3007500)
• Basic Scientific Research and Operation Foundation of CAMS (Grants No. 2023Z024 & 2023Z003)
• Basic Research Fund of CAMS (2025Y003)

Citation

@article{Liu2026Mechanisms,
  author = {Liu, Qiaohua and Li, Lun},
  title = {Mechanisms of two types of summer persistent extreme precipitation events in the northeastern Tibetan Plateau},
  journal = {Weather and Climate Extremes},
  year = {2026},
  doi = {10.1016/j.wace.2026.100853},
  url = {https://doi.org/10.1016/j.wace.2026.100853}
}