Mohanty et al. (2025) Precipitation bursts in northern Australia with and without preceding heatwaves

Identification

• Journal: Weather and Climate Extremes
• Year: 2025
• Date: 2025-12-12
• Authors: Sarthak Mohanty, Nikhil Garg, Nandini Ramesh, Mahesh Prakash
• DOI: 10.1016/j.wace.2025.100845

Research Groups

• Data61, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia
• Center for Climate Physics, Institute for Basic Science, Republic of Korea
• Pusan National University, Republic of Korea

Short Summary

This study investigates the interaction between heatwaves and precipitation bursts in Northern Australia, revealing that heatwaves precondition the atmosphere, leading to stronger, more prolonged, and dynamically driven rainfall bursts compared to independent events. The research highlights the critical role of atmospheric circulation in shaping these compound extremes and their distinct responses to large-scale climate modes.

Objective

• To investigate the interaction between heatwaves and precipitation bursts in Northern Australia during the pre- and post-monsoon seasons.
• To systematically contrast precipitation bursts preceded by heatwaves with those occurring independently, using a vertically integrated moisture budget framework.
• To explore how large-scale climate modes, such as the Madden–Julian Oscillation (MJO) and El Niño–Southern Oscillation (ENSO), modulate these interactions.
• To improve understanding of the dynamics of compound heatwave-precipitation events and contribute to risk mitigation strategies.

Study Configuration

• Spatial Scale: Tropical zone of Northern Australia.
• Temporal Scale: 55-year period from 1960 to 2014, focusing on pre-monsoon (October–November) and post-monsoon (March–April) seasons.

Methodology and Data

• Models used:
  • Vertically integrated moisture budget framework, including decomposition into vertical and horizontal moisture advection, evaporation, and moisture tendency.
  • Decomposition of vertical moisture advection into dynamic and thermodynamic components.
  • Moist Static Energy (MSE) budget analysis, including Dry Static Energy (DSE) and moisture components, to analyze convective structure.
• Data sources:
  • European Centre for Medium-Range Weather Forecasts 5th generation reanalysis (ERA5) with a horizontal grid spacing of 0.25° × 0.25° (8 pressure levels).
  • Real-time multivariate MJO index (RMM) from the Bureau of Meteorology (1974–2014).
  • El Niño–Southern Oscillation (ENSO) classification from the National Oceanic and Atmospheric Administration’s Climate Prediction Center (NOAA CPC).

Main Results

• Heatwave-associated precipitation bursts (BurstsWH) exhibit stronger and more prolonged convective activity, resulting in intensified peak precipitation and delayed maxima (by approximately one day) compared to independently occurring bursts (BurstsnoH).
• BurstsWH show a pronounced buildup of Convective Available Potential Energy (CAPE), peaking near the heatwave's end at approximately 100 J/kg, and increased total column water vapor (TCWV) from 4 days prior to the burst.
• Vertical moisture advection is the dominant mechanism driving precipitation variability in both types of bursts, accounting for over 70% of the total variance in column-integrated moisture flux.
• The dynamic component of vertical moisture advection, driven by circulation anomalies, plays a more substantial role (over 75% contribution) than the thermodynamic component in driving changes in vertical moisture advection for both burst types.
• BurstsWH exhibit stronger convective activity and a more pronounced top-heavy atmospheric structure in the MSE budget, indicative of deeper convection, compared to BurstsnoH.
• Heatwave-associated bursts coincide with anomalously low mean sea level pressure (MSLP) and enhanced cyclonic circulation over Northern Australia, providing sustained low-level convergence and upward motion.
• BurstsnoH events are most frequent and intense during La Niña years (41 events, mean day-0 precipitation of 68 W/m²), consistent with established ENSO–rainfall relationships.
• In contrast, BurstsWH events are more frequent and intense during El Niño years (11 events, mean day-0 precipitation of 74 W/m²), suggesting that warmer, drier El Niño conditions precondition the atmosphere for stronger compound events.
• While the active MJO phase appears to enhance precipitation for BurstsWH, statistical robustness tests (bootstrap, permutation, leave-one-out) indicate that this finding is tentative and highly sensitive to individual events due to small sample sizes.

Contributions

• This study is the first to systematically examine the interaction between heatwaves and precipitation bursts in Northern Australia, filling a critical knowledge gap in tropical compound extreme events.
• It quantitatively demonstrates that heatwaves precondition the atmosphere by enhancing instability (CAPE) and moisture availability, leading to more intense and prolonged subsequent rainfall bursts.
• The research identifies atmospheric circulation changes, specifically the dynamic component of vertical moisture advection and enhanced cyclonic circulation, as the primary drivers for the intensification of compound heatwave-precipitation events.
• It reveals contrasting influences of ENSO on heatwave-associated versus independent precipitation bursts, highlighting that compound events respond differently to large-scale climate variability and should be treated separately in climate understanding and prediction.
• The findings offer practical implications for anticipating heightened hydrometeorological risks in Northern Australia, particularly when heatwaves precede intense precipitation, though further research with larger datasets is needed to confirm MJO-related synergies.

Funding

• Climate Services for Agriculture initiative within Data61 at the Commonwealth Scientific and Industrial Research Organisation (CSIRO)
• National Computational Infrastructure (NCI), supported by the Australian Government

Citation

@article{Mohanty2025Precipitation,
  author = {Mohanty, Sarthak and Garg, Nikhil and Ramesh, Nandini and Prakash, Mahesh},
  title = {Precipitation bursts in northern Australia with and without preceding heatwaves},
  journal = {Weather and Climate Extremes},
  year = {2025},
  doi = {10.1016/j.wace.2025.100845},
  url = {https://doi.org/10.1016/j.wace.2025.100845}
}