Lopez-Ramirez et al. (2026) Characterizing dry and humid heatwaves in Southern South America: regional trends and large-scale climate drivers

Identification

• Journal: Climate Dynamics
• Year: 2026
• Date: 2026-01-06
• Authors: Agustina Lopez-Ramirez, Mariana Barrucand, Soledad Collazo
• DOI: 10.1007/s00382-025-08016-9

Research Groups

• Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias de La Atmósfera y los Océanos (DCAO-FCEN-UBA), Universidad de Buenos Aires, Buenos Aires, Argentina
• Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
• Departamento de Física de La Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Madrid, Spain
• Instituto de Geociencias (IGEO), Consejo Superior de Investigaciones Científicas-Universidad Complutense de Madrid (CSIC-UCM), Madrid, Spain

Short Summary

This study characterized the spatiotemporal variability and trends of dry and humid compound heatwaves in Southern South America (1979-2018) and investigated the influence of large-scale climate drivers. It found an increase in dry and sequential humid heatwaves, with specific climate driver combinations enhancing dry events while suppressing humid ones.

Objective

• To characterize the spatiotemporal variability and trends (frequency, duration, intensity, spatial extent) of dry and humid compound heatwaves in Southern South America during the warm season (October–March) from 1979 to 2018.
• To investigate the modulation of these compound heatwaves by individual and combined phases of large-scale climate drivers (El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Indian Ocean Dipole (IOD), and Southern Annular Mode (SAM)).

Study Configuration

• Spatial Scale: Southern South America (SSA), covering 132 meteorological stations, categorized into 6 regions (northern SSA, central-eastern SSA, central Argentina and northern Argentinian Patagonia, central Chile, Argentinian Patagonia and southern Chile, northern Chile).
• Temporal Scale: Warm season (October–March) over the period 1979–2018 (40 years). The study period was divided into two subperiods: 1979–1998 and 1999–2018 for trend analysis.

Methodology and Data

• Models used:
  • Heatwave definition: Daily maximum temperature exceeding the 90th percentile (based on 1981–2010 period with a 15-day moving window) for at least three consecutive days.
  • Precipitation conditions: Standardized Precipitation Index (SPI) for 1-month (SPI1) and 3-month (SPI3) durations.
  • Compound event types: Simultaneous Dry Heatwave (SIDH), Sequential Dry Heatwave (SEDH), Simultaneous Humid Heatwave (SIHH), Sequential Humid Heatwave (SEHH).
  • Regionalization: Ward hierarchical clustering method.
  • Statistical tests: Kolmogorov–Smirnov test (for spatial extent ECDF differences), Fisher’s exact test (for association between climate drivers and events), Mann–Kendall test (for trends).
• Data sources:
  • Daily maximum temperature and precipitation records from 132 meteorological stations in SSA.
  • Climate drivers indices: Oceanic Niño Index (ONI) for ENSO, Pacific Decadal Oscillation (PDO) index, Indian Ocean Dipole (IOD) index, and Southern Annular Mode (SAM) index, obtained from public online repositories (Climate Prediction Center, NOAA PSL, NERC-BAS).

Main Results

• Dry compound heatwaves (SIDH and SEDH) were considerably more frequent than humid ones, particularly in central and northeastern Argentina. Simultaneous humid heatwaves (SIHH) were the least common.
• Comparing the periods 1979–1998 and 1999–2018, an increase in the frequency and spatial extent of dry events (SIDH and SEDH) and sequential humid heatwaves (SEHH) was observed in recent decades across SSA.
• Regionally, SIDH showed significant positive trends in compound heatwave days (CoHWds) in central-eastern SSA, central Argentina, and southern SSA. SEDH increased in central Chile, and SEHH increased in central Argentina.
• La Niña conditions and negative Pacific Decadal Oscillation (PDO−) phases were significantly associated with an increased frequency of dry compound heatwaves (SIDH and SEDH).
• El Niño conditions and positive PDO (PDO+) phases tended to favor humid heatwaves (SIHH and SEHH), though with limited statistical significance.
• The influence of the Indian Ocean Dipole (IOD) and Southern Annular Mode (SAM) on compound heatwaves was generally weaker and more spatially limited when considered individually.
• The combined phase of La Niña, negative PDO, negative IOD, and positive SAM (DC 11) was identified as one of the most influential configurations, promoting a higher occurrence and greater spatial extent of dry heatwaves while suppressing humid ones.

Contributions

• Provides a comprehensive characterization of the spatiotemporal variability, trends, and large-scale climate driver influences on both dry and humid compound heatwaves in Southern South America.
• Identifies specific regional hotspots and temporal shifts, including increased frequency and spatial extent of dry and sequential humid heatwaves, over recent decades (1999-2018 vs. 1979-1998).
• Offers a detailed analysis of the individual and combined roles of four major climate drivers (ENSO, PDO, IOD, SAM) in modulating compound heatwave occurrence and spatial extent, highlighting the amplifying/suppressing effects of specific multi-driver combinations.
• Establishes a framework and definitions for characterizing compound heatwaves that can be applied to global and regional climate models, supporting future climate change projections and risk assessments.

Funding

• PICT2019-2019-02933
• CONICET PIP 0333 (2021–2023)
• UBACyT 20020220200111BA
• European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 847635 (UNA4CAREER)

Citation

@article{LopezRamirez2026Characterizing,
  author = {Lopez-Ramirez, Agustina and Barrucand, Mariana and Collazo, Soledad},
  title = {Characterizing dry and humid heatwaves in Southern South America: regional trends and large-scale climate drivers},
  journal = {Climate Dynamics},
  year = {2026},
  doi = {10.1007/s00382-025-08016-9},
  url = {https://doi.org/10.1007/s00382-025-08016-9}
}