Pradhan et al. (2025) Atmospheric Rivers intensify extreme precipitation and flooding across Australia

Identification

• Journal: Weather and Climate Extremes
• Year: 2025
• Date: 2025-10-09
• Authors: Shekhar Pradhan, Conrad Wasko, Murray Peel
• DOI: 10.1016/j.wace.2025.100812

Research Groups

• Department of Infrastructure Engineering, The University of Melbourne, Melbourne, Victoria, Australia
• School of Civil Engineering, The University of Sydney, Sydney, New South Wales, Australia

Short Summary

This study quantifies the impact of Atmospheric Rivers (ARs) on extreme precipitation and flooding across Australia, revealing that ARs significantly increase the magnitude (20–70% higher) and frequency (2 to 12 times shorter return periods) of these events, particularly in southeast Australia.

Objective

• To determine the percentage of peak precipitation and streamflow events associated with Atmospheric Rivers (ARs) across Australia.
• To quantify how ARs affect the tail behavior of extreme precipitation and flooding events.
• To analyze how the frequency of extreme events varies across Australia's different climatic zones with and without ARs.

Study Configuration

• Spatial Scale: Continental Australia, utilizing 467 Hydrologic Reference Stations (HRS) at the catchment scale.
• Temporal Scale: Data analysis period from 1980 to 2019 (40 years).

Methodology and Data

• Models used:
  • Peak Over Threshold (POT) approach for identifying extreme events (99th percentile threshold, 7-day declustering).
  • Generalized Pareto Distribution (GPD) for fitting the tail behavior of extreme events.
  • Generalized Maximum Likelihood Estimation (GMLE) for GPD parameter estimation.
  • Two global AR detection methods: Mundhenk et al. (2016) (Mundhenk) and Reid et al. (2020) (Reid500).
  • R programming language, specifically the hydroEvents package with the eventPOT() function.
• Data sources:
  • Daily streamflow data: 467 Hydrologic Reference Stations (HRS) from the Australian Bureau of Meteorology (BOM).
  • Gridded daily precipitation data: Australian Water Availability Project (AWAP) at 0.05° × 0.05° angular resolution.
  • Atmospheric River (AR) data: Atmospheric River Tracking Method Intercomparison Project (ARTMIP) Tier 2 Reanalysis data from the Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) at 0.625° × 0.5° angular resolution.

Main Results

• Southeast Australia exhibits the highest AR concurrence (approximately 75–100%) with extreme precipitation and streamflow events.
• The median magnitude of extreme precipitation and streamflow events is 20–70% higher when an AR is present.
• The return periods of extreme flood and precipitation events of a given magnitude are, on average, 2 to 12 times shorter when they coincide with an AR compared to when they do not.
• For 5-year non-AR return period events, ARs can make them up to 6 times more frequent. For rarer 10- and 20-year non-AR return period events, ARs can increase their frequency by more than 12 times.
• Precipitation events show the strongest association with ARs within 0–1 days of AR occurrence, while streamflow events exhibit a delayed response, becoming more prominent at 3–5 day lags.
• Northern Australian regions (Monsoonal North and Wet Tropics) show lower AR influence, with other drivers like monsoonal precipitation and tropical cyclones being more dominant.

Contributions

• Presents the first continental-scale analysis of the tail behavior of AR-induced extreme precipitation and flooding at the catchment level for Australia.
• Quantifies the significant impact of ARs on both the magnitude and frequency (return periods) of extreme hydrometeorological events across Australia.
• Highlights the critical need to integrate AR impacts into hydrological modeling for improved water resource management and flood risk assessment.
• Suggests that flood frequency curves should account for AR influence by separating events into AR-driven and non-AR-driven populations due to distinct underlying mechanisms.

Funding

• University of Sydney Horizon Fellowship (Conrad Wasko)
• Australian Research Council (Conrad Wasko)

Citation

@article{Pradhan2025Atmospheric,
  author = {Pradhan, Shekhar and Wasko, Conrad and Peel, Murray},
  title = {Atmospheric Rivers intensify extreme precipitation and flooding across Australia},
  journal = {Weather and Climate Extremes},
  year = {2025},
  doi = {10.1016/j.wace.2025.100812},
  url = {https://doi.org/10.1016/j.wace.2025.100812}
}