Indonesia Could See 19,300 Additional Heat-Related Deaths During El Niño. What Does That Number Mean?

By: Gert Tobing, Dyna Rochmyaningsih, and Ilham A. Ridlo

Around 19.000 additional heat-related deaths are projected in Indonesia between September 2026 and February 2027, according to a new analysis by the Climate Impact Lab. Scientists call for better heat warnings and preventive action plans for vulnerable populations. 

Published by Climate Impact Lab (23/9/2026) at the University of Chicago’s Energy Policy Institute, the study estimates how temperature increases affect mortality across 24,378 regions in 40+ countries, accounting for local climate, income, and adaptive capacity. 

Globally, the report projects 451,000 heat-related deaths during this El Niño compared to a normal year. The report frames the current temperatures as a “postcard from the future”. A remark highlights that the temperature caused by super El Niño now will be the new normal within 20 years.

The analysis projects a particularly high absolute heat-related mortality burden for Indonesia during this Super El Niño cycle. Indonesia is projected to experience around 19,300 additional heat-related deaths, a higher absolute number than the Philippines (6,500) and Vietnam (5,600), and the largest projected total in Southeast Asia.

“Indonesia has the second largest number of forecasted deaths for the next 6 months in our projections,” said Emily Grover-Kopec, report co-author and director at the Rhodium Group, in a written response to ScienceWatchdog.id. Approximately 10,400 of the deaths are concentrated from December 2026 through February 2027.

According to the study, the warning is meant as an early call to take mitigative actions. Most of the projected deaths have not happened yet, leaving several months in which governments could potentially reduce the health burden.

This projection arrives as Indonesia is already experiencing Super El Niño. According to Erma Yulihastin, research professor at BRIN’s Center for Climate and Atmosphere, El Niño intensity has been rising 0.1°C per week since February 2026, reaching 2.54°C and predicted to exceed 3.5°C by December, the longest and strongest on record. (BMKG reported 2.76 °C in their September release)

Additionally, fires have burned 895,657 hectares across Indonesia from January to August 2026 according to Nusantara Atlas. The Ministry of Health reported over 165,000 respiratory infection cases as of August. Indonesia’s longest river, the Kapuas, has dried up in West Kalimantan, the hardest hit province.

But these news headlines are just a tip of iceberg, scientists say. The WHO states that heat can affect health both directly and indirectly. When temperatures rise, people are vulnerable to heat stress. This heat stress may disrupt people’s body temperature, causing heat strokes and worsen chronic health risks such as existing cardiovascular, mental, and respiratory conditions.

“The primary mechanisms by which high temperature affects human health and causes death are through stress to the cardiovascular and respiratory systems, dehydration, and heat stroke,” said Grover-Kopec. 

Most of these deaths will not be recorded as “death by heat.” Instead, they will appear as cardiac arrests, respiratory failures, and strokes. The WHO defines excess mortality measures the gap between total deaths in a given period and what would normally be expected in an average year. 

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Between Warnings and Methodological Notes 

Grover-Kopec says her team’s projection draws on a 2022 study by the Climate Impact Lab that investigated the relationship between temperature and mortality across 41 countries. Using around 399 million deaths in 1996-2025 period, the study built a mathematical model that showed how excess deaths increase with rising temperatures. Some factors like local climate, income levels, and adaptive capacity were also considered to see how each country produce different outcomes in the model.

For this report, those heat and death relationships were combined with six-month temperature forecasts from the European Centre for Medium-Range Weather Forecasts seasonal system (one of the world’s most reliable forecasting tools) to project excess deaths during this El Niño period.

“We start with forecasted temperature anomalies for the next six months from the ECMWF. We then use the relationships from the 2022 study, which estimate excess temperature-related deaths based on temperature, to translate the forecasted temperature to excess heat deaths”, said Grover-Kopec.

This is the first time the 2022 model has been applied to seasonal forecasting as it was originally designed for long-term projections spanning decades, not six-month windows.

“This is the first time we’ve used the 2022 study for such a near-term use case…with the main difference being that we are using seasonal temperature forecasts for the next 6 months in the current work, rather than temperature projections from climate models for the next 75 years”, explained Grover-Kopec, to describe the application as a novel use of an established framework.

Why Indonesia Ranks so High?

The high estimated death number for Indonesia is mainly due to its high population and the ever-increasing temperature anomaly, according to Grover-Kopec. A forecasted anomaly of 1-2°C temperature increase that comes when Indonesia already experiences heat-related stress puts Indonesia high in the heat-related deaths projection.

What Can Be Done

The report showed interventions proven to reduce heat deaths such as early warning systems, cooling centers, hydration stations, worker protections, and expanded health system outreach to vulnerable populations. Critically, most of Indonesia’s projected deaths are still ahead in December to February. That window gives an opportunity to take action, according to the report.

“The situation could get worse,” Yulihastin told Indonesian Science Affairs in an earlier interview.

El Niño, she noted, is a contributing factor to Indonesia’s current crisis, not the sole cause. Peatland mismanagement and intentional burning remain the primary drivers of fires. But when extreme heat signals are this clear, she argued, regulations should be enforced before the damage intensifies.

Indonesia’s Ministry of Health has prepared masks, oxygen, and health logistics to battle toxic gases produced by current forest fires. Meanwhile, Indonesia’s National Disaster Management Agency (BNPB) treats the Climate Impact Lab’s projection of 19,300 deaths as an actionable early warning rather than a definitive outcome. 

Acting Head of Data, Information, and Disaster Communication at BNPB, Berton SP Panjaitan, emphasized that while the figures serve as a critical alert, they do not account for secondary El Niño impacts such as severe droughts and peatland or forest fires, said Berton to Republika.

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Writing: Gert Tobing
Editing: Dyna Rochmyaningsih, Ilham Ridlo
Layout/Data visualization: Ilham A. Ridlo
Photo/Image: Melvinas Priananda