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Peer-reviewedCC BY 4.0Npj Climate and Atmospheric Science

Synoptic-to-interannual drivers of humid heat variability in equatorial Southeast Asia

  • Anistia M. Hidayat1,2
  • Cathryn E. Birch1
  • Lawrence S. Jackson1
  • Juliane Schwendike1
  • Claudio Sanchez3
  • Adrian J. Matthews4
4 affiliations
  1. 1School of Earth and Environment, University of Leeds, Leeds, UK
  2. 2Meteorological, Climatological, and Geophysical Agency (BMKG), Jakarta, Indonesia
  3. 3Met Office, Exeter, UK
  4. 4School of Environmental Sciences, University of East Anglia, Norwich, UK
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Abstract

As the Earth continues to warm, humid heat extremes (HHEs) have emerged as a widely recognised threat to human health in equatorial Southeast Asia (SEA). While most studies have focused on climate trends, this study presents a comprehensive analysis of the synoptic and large-scale drivers of HHEs. On daily timescales, both the Madden-Julian Oscillation (MJO) and Kelvin waves are the leading modes of HHE variability. HHE risk increases by 1.2–1.4x during the dry-to-wet transition of the MJO phases, predominantly driven by increased near-surface specific humidity preceding the peak rainfall anomaly in phase 2 and increased shortwave radiation due to reduced cloud cover in phase 8. HHE risk increases by 1.3–2.0x during the dry phase of equatorial Kelvin waves, which drives subsidence and increased shortwave warming. On interannual timescales, El Niño is the leading driver, under which HHE risk increases 3 – 5x. Despite the limited overlap (19%) between wet- and dry-bulb temperature extremes, the differences in their temperature and humidity conditions, and their drivers, are small. This understanding lays the groundwork for short-range to seasonal forecasts, which are a crucial component of much-needed heat early warning systems.

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Cite

BibTeXRIS
BibTeX
@article{hidayat2026synoptictointerannual,
  title = {{Synoptic-to-interannual drivers of humid heat variability in equatorial Southeast Asia}},
  author = {Anistia M. Hidayat and Cathryn E. Birch and Lawrence S. Jackson and Juliane Schwendike and Claudio Sanchez and Adrian J. Matthews},
  journal = {Npj Climate and Atmospheric Science},
  year = {2026},
  month = jun,
  doi = {10.1038/s41612-026-01451-3},
  url = {https://doi.org/10.1038/s41612-026-01451-3},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Synoptic-to-interannual drivers of humid heat variability in equatorial Southeast Asia
AU  - Anistia M. Hidayat
AU  - Cathryn E. Birch
AU  - Lawrence S. Jackson
AU  - Juliane Schwendike
AU  - Claudio Sanchez
AU  - Adrian J. Matthews
PY  - 2026
DA  - 2026/06/09
JO  - Npj Climate and Atmospheric Science
DO  - 10.1038/s41612-026-01451-3
UR  - https://doi.org/10.1038/s41612-026-01451-3
AB  - As the Earth continues to warm, humid heat extremes (HHEs) have emerged as a widely recognised threat to human health in equatorial Southeast Asia (SEA). While most studies have focused on climate trends, this study presents a comprehensive analysis of the synoptic and large-scale drivers of HHEs. On daily timescales, both the Madden-Julian Oscillation (MJO) and Kelvin waves are the leading modes of HHE variability. HHE risk increases by 1.2–1.4x during the dry-to-wet transition of the MJO phases, predominantly driven by increased near-surface specific humidity preceding the peak rainfall anomaly in phase 2 and increased shortwave radiation due to reduced cloud cover in phase 8. HHE risk increases by 1.3–2.0x during the dry phase of equatorial Kelvin waves, which drives subsidence and increased shortwave warming. On interannual timescales, El Niño is the leading driver, under which HHE risk increases 3 – 5x. Despite the limited overlap (19%) between wet- and dry-bulb temperature extremes, the differences in their temperature and humidity conditions, and their drivers, are small. This understanding lays the groundwork for short-range to seasonal forecasts, which are a crucial component of much-needed heat early warning systems.
SN  - 2397-3722
ER  -