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Widespread heat stress will become the norm in a warming Southeast Asia

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Abstract

Southeast Asia faces growing risks from extreme heat under climate change, yet existing assessments do not fully account for physiological impacts and population-level exposure, particularly at resolutions relevant for planning. Here we present a comprehensive evaluation of future heat stress in the region by integrating three methodological innovations: physiologically relevant bio-climatic indices, spatially explicit population exposure, and sub-daily temporal resolution. Using the Universal Thermal Climate Index (UTCI) and Wet-Bulb Globe Temperature (WBGT), we assess heat stress across Southeast Asia at (22{times }22) km spatial and 3-hourly temporal resolution under low- and high-emissions scenarios. We combine these projections with population data to identify where and when risks are most acute. Our results show that even by the near-future (2030–2059), exposure to life-threatening extremes (UTCI > (46,^{circ })C, WBGT > (33,^{circ })C) increases sharply, by factors of 2.8–4.6 (UTCI) and 4.6–7.9 (WBGT) relative to historical levels. The number of people exposed to at least one consecutive week of extreme UTCI grows from 9 million historically to 23–28 million under RCP2.6 and RCP8.5, while extreme WBGT exposure increases from 0.1 million to 7–17 million. Continental Southeast Asia, including Myanmar, Thailand, and Cambodia, faces the most acute risks, with 6–9 hours of severe heat stress per day during peak months. By the far-future (2070–2099) under RCP8.5, exposure escalates to catastrophic levels, with up to 200 days per year of unsafe conditions and exposed populations increasing more than tenfold. Our findings show that dangerous levels of heat stress will emerge within decades, underscoring the urgency of adaptation and the benefits of strong mitigation.

Data availability

The UTCI and WBGT results computed in this study are partially available at https://doi.org/10.5281/zenodo.17020558 and the full dataset can be requested from the lead author (Sonali Manimaran, [email protected]). REMO RCM data are partially available through https://esgf-metagrid.cloud.dkrz.de/, and the full dataset can be requested from the Climate Service Centre Germany (GERICS). The historical population data can be accessed through https://human-settlement.emergency.copernicus.eu/download.php, and future population data through https://figshare.com/articles/dataset/Projecting_1_km-grid_population_distributions_from_2020_to_2100_globally_under_shared_socioeconomic_pathways/19608594/2.

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Funding

This work is supported by the following grants: the Helmholtz Information & Data Science Academy (HIDA) Visiting Researcher Grant to S.M.; the Ministry of Education, Singapore, under its MOE AcRF Tier 3 Award MOE2019-T3-1-004 to the Southeast Asia Sea-level (SEA2) Programme, supporting S.M., I.K., and D.L., and the MOE AcRF Tier 2 Award MOE-T2EP50222-0016, supporting D.W. and D.L.; and the Helmholtz Association under the programme “Changing Earth – Sustaining our Future”, funding C.N., L.L., and L.B.

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Authors and Affiliations

  1. Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Ave, Singapore, 639798, Singapore

    Sonali Manimaran, Dennis Wagenaar, Indraneel Kasmalkar & David Lallemant

  2. Asian School of the Environment, Nanyang Technological University, 50 Nanyang Ave, Singapore, 639798, Singapore

    Sonali Manimaran, Dennis Wagenaar & David Lallemant

  3. Climate Service Center Germany (GERICS), Helmholtz-Zentrum Hereon, Fischertwiete 1, Hamburg, 20095, Germany

    Christine Nam & Laurens M. Bouwer

  4. Copernicus Climate Change Service, German Weather Service (DWD), Bernhard-Nocht-Straße 76, Hamburg, 20359, Germany

    Ludwig Lierhammer

  5. Institute of Geography, University of Hamburg, Bundesstraße 55, Hamburg, 20146, Germany

    Laurens M. Bouwer

Authors

  1. Sonali Manimaran
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  2. Dennis Wagenaar
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  3. Christine Nam
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  4. Indraneel Kasmalkar
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  5. Ludwig Lierhammer
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  7. David Lallemant
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Contributions

S.M., D.W., C.N., L.B., and D.L. conceived and designed the study. S.M., D.W., C.N., and L.L. developed the methodology and software. S.M. performed the formal analysis and visualisation, and wrote the original draft. All authors contributed to the reviewing and editing of the manuscript. L.B. and D.L. supervised the project.

Corresponding author

Correspondence to
Sonali Manimaran.

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Manimaran, S., Wagenaar, D., Nam, C. et al. Widespread heat stress will become the norm in a warming Southeast Asia.
Sci Rep (2025). https://doi.org/10.1038/s41598-025-28817-6

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  • DOI: https://doi.org/10.1038/s41598-025-28817-6

Keywords

  • Heat stress
  • Extreme heat
  • Climate change
  • Exposure
  • Southeast Asia
  • UTCI
  • WBGT

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