Pérez-Alarcón et al. (2026) Unravelling the drivers of the April–May 2024 extreme precipitation event in Rio Grande do Sul

Identification

• Journal: Atmospheric Research
• Year: 2026
• Date: 2026-01-12
• Authors: Albenis Pérez-Alarcón, Rogert Sorí, Milica Stojanovic, Renata Libonati, Ricardo M. Trigo, Raquel Nieto, Luis Gimeno
• DOI: 10.1016/j.atmosres.2026.108773

Research Groups

• Centro de Investigación Mariña, Universidade de Vigo, Environmental Physics Laboratory (EPhysLab), Ourense, Spain
• Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
• Departamento de Meteorologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
• Climate System Research Unit, UVigo-CESGA, Santiago de Compostela, Spain

Short Summary

This study identifies the atmospheric drivers and moisture sources of the April–May 2024 extreme precipitation and flooding event in Rio Grande do Sul, Brazil, revealing a persistent atmospheric dipole, reinforced by a heat wave, that channeled anomalous Amazonian moisture via an intensified South American Low-Level Jet.

Objective

• To identify the atmospheric drivers and moisture sources fueling the April–May 2024 extreme precipitation event in Rio Grande do Sul, Brazil.
• To examine changes in moisture contributions by comparing the RS 2024 event with similar past events using an analogue-based analysis.

Study Configuration

• Spatial Scale: The study focuses on Rio Grande do Sul (RS), Brazil. The analogue search was performed over a domain bounded by 100°W–10°E and 0–55°S. Moisture source analysis was conducted on a 0.5° × 0.5° grid. Precipitation data has a 0.1° × 0.1° resolution, while ERA5 reanalysis data is at 0.25° × 0.25° (atmospheric variables) and 0.5° × 0.5° (FLEXPART driven fields).
• Temporal Scale: The extreme event duration was defined from 26 April to 8 May 2024, with a peak period from 29 April to 3 May 2024. Anomalies and analogue analyses were computed relative to a 1991–2020 reference period. Lagrangian moisture tracking was performed backward for up to 10 days. Data were used at 1-hour (ERA5) and 3-hourly (MSWEP, FLEXPART) frequencies.

Methodology and Data

• Models used:
  • FLEXible PARTicle (FLEXPART v10.4) dispersion model for Lagrangian moisture tracking.
  • Lagrangian Atmospheric Moisture and Heat Tracking (LATTIN) tool for moisture source identification.
  • Analogue-based methodology (Faranda et al., 2022) for identifying similar past atmospheric circulation patterns.
• Data sources:
  • European Centre for Medium-Range Weather Forecasts ERA5 reanalysis for atmospheric variables (integrated water vapour transport (IVT), mean sea level pressure (MSLP), geopotential height at 500 hPa, 2-meter air temperature).
  • Multi-Source Weighted-Ensemble Precipitation (MSWEP) dataset for high-resolution precipitation data.
  • Physical Sciences Laboratory U.S National Oceanic and Atmospheric Administration (NOAA) for large-scale climate variability indices (El Niño-Southern Oscillation (ENSO), Tropical Southern Atlantic Index (TSA), Atlantic Meridional Mode (AMM), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO)).

Main Results

• The April–May 2024 event in Rio Grande do Sul (RS) was characterized by extreme accumulated precipitation, exceeding 480 mm in central and northeastern areas during the event (26 April – 8 May) and over 450 mm during the 5-day peak (29 April – 3 May).
• The primary atmospheric driver was a persistent, quasi-stationary dipole configuration consisting of a blocking high-pressure system over the South Atlantic and a deep low-pressure system over southern South America.
• This dipole was reinforced by a concurrent heat wave over central and southeastern Brazil, which amplified the blocking high and created a strong temperature gradient, enhancing atmospheric instability over RS.
• An intensified South American Low-Level Jet (SALLJ) channeled a sustained, atmospheric river-like moisture transport from the Amazon region and the north-south corridor over the Pantanal towards RS.
• Lagrangian analysis revealed that the highest moisture contribution occurred predominantly 1–3 days before the precipitation over RS, with a mean water vapor residence time of 2.4 ± 0.3 days.
• An analogue-based analysis showed that while the Mean Sea Level Pressure (MSLP) pattern was uncommon but not unique within the 1991–2020 reference period, the RS 2024 event exhibited significantly enhanced moisture transport and uptake from the Amazon compared to similar past occurrences.
• The event displayed lower predictability and persistence of the MSLP pattern compared to its analogues.
• The event is best understood as a high-impact compound event, resulting from the complex interplay of the quasi-stationary dipole, the thermal gradient from the heat wave, and the atmospheric river-like moisture flow via the SALLJ.

Contributions

• Provides a comprehensive, multi-faceted analysis of the unprecedented April–May 2024 extreme precipitation event in Rio Grande do Sul, Brazil, integrating atmospheric dynamics, moisture transport, and analogue-based contextualization.
• Identifies the specific, dynamically linked atmospheric drivers—a quasi-stationary dipole, a reinforcing heat wave, and an intensified South American Low-Level Jet—that converged to produce this high-impact compound event.
• Quantifies the rapid moisture supply, showing that the most significant moisture uptake occurred within 1–3 days before precipitation, primarily from the Amazon and Pantanal regions.
• Demonstrates, through an analogue-based analysis, that while the large-scale MSLP pattern was uncommon, the magnitude of moisture transport and uptake from the Amazon during the 2024 event was anomalously enhanced compared to similar past events.
• Reinforces the critical need for an improved understanding of climate-weather interactions and the development of comprehensive risk management strategies for compound extreme events in a changing climate.

Funding

• Xunta de Galicia (Postdoctoral grant No. ED481B − 2023/016, Excelencia-ED431F-2024/03 project, SETESTRELO and APALPADOR projects (grants PID2021 − 122314OB-I00 and PID2024-155515NB-I00), and grant ED431C2021/44).
• Ministerio de Ciencia, Innovación y Universidades, Spain (MICIU/AEI/10.13039/501100011033) and the European Union Next Generation EU/PRTR (grant RYC2021 − 034044-I).
• Portuguese Science Foundation (FCT) through the project AMOTHEC (DRI/India/0098/2020).
• CNPQ (grant 443285/2023-3 and 311487/2021-1) and FAPERJ (grant E-26/210078/2023 and E-26/200.329/2023).
• Universidade de Vigo/Consorcio Interuniversitario do Sistema Universitario de Galicia (Universidade de Vigo/CISUG agreement with Elsevier) for Open Access.

Citation

@article{PérezAlarcón2026Unravelling,
  author = {Pérez-Alarcón, Albenis and Sorí, Rogert and Stojanovic, Milica and Libonati, Renata and Trigo, Ricardo M. and Nieto, Raquel and Gimeno, Luis},
  title = {Unravelling the drivers of the April–May 2024 extreme precipitation event in Rio Grande do Sul},
  journal = {Atmospheric Research},
  year = {2026},
  doi = {10.1016/j.atmosres.2026.108773},
  url = {https://doi.org/10.1016/j.atmosres.2026.108773}
}