The Hidden Death Toll of the 2025 Iberian Blackout: +167 Excess Deaths in Spain
On April 28, 2025, the Iberian Peninsula experienced one of the most widespread power outages in modern European history. For roughly ten hours, mainland Spain and Portugal lost virtually all electrical power, affecting more than 50 million people. Communications networks failed. Transport ground to a halt. Hospitals switched to backup generators. Eight deaths were directly attributed to the blackout in the immediate aftermath.
That direct death toll, it now appears, told only part of the story.
A study published in Nature Communications by researchers at Imperial College London and the University of Lausanne has found that the blackout was associated with a significant increase in mortality in Spain in the days following the event, an increase that official tallies did not capture.
The Data
Garyfallos Konstantinoudis and Julien Riou analyzed all-cause mortality data from Spain and Portugal around the date of the blackout, using statistical models to estimate how many deaths would have been expected under normal conditions and comparing that to the actual number recorded.
On the day of the blackout itself, there was little evidence of excess mortality, consistent with the fact that the eight directly reported deaths were within normal statistical variation. But over the next two days, mortality in Spain rose substantially: an estimated 167 excess deaths (95 percent credible interval: +28 to +300), representing a 2.4 percent relative increase.
The increase was not evenly distributed across the population. The excess was concentrated among women aged 85 and older, the most vulnerable demographic in any public health emergency. Regional differences also emerged, though the researchers caution that the drivers of those differences remain uncertain. Variation in outage severity, underlying population vulnerabilities, and differences in local health system and infrastructure conditions may all have played a role.
In Portugal, by contrast, no significant excess mortality was detected.
Direct and Indirect Effects
The study distinguishes between the direct effects of a blackout, medical equipment failure, inability to power ventilators or dialysis machines, accidents in darkness, and indirect effects, which are harder to measure but may be more consequential. Disrupted healthcare is a primary concern: when hospitals lose power, elective procedures are cancelled, emergency departments are stretched, and patients who would normally seek care may not be able to reach a facility. Pharmacies may close. Home medical devices may fail.
Some of these indirect effects can persist beyond the duration of the blackout itself, which may explain why the excess deaths the researchers observed occurred not on April 28 but on April 29 and 30.
The findings are consistent with a separate analysis published in Eurosurveillance in 2025, which used Spain’s MoMo mortality monitoring system to detect what appeared to be 147 excess deaths over three days following the blackout. While less precise than the new analysis, that earlier report flagged the same pattern: a mortality signal that was not obvious in real time but became visible with systematic analysis.
A Growing Concern
The 2025 Iberian blackout was triggered by a combination of technical failures that are still under investigation by European grid operators. An initial report from the European Network of Transmission System Operators for Electricity ruled out the hypothesis that excess renewable generation caused the outage, but the full investigation is ongoing.
What the new study makes clear is that the health consequences of such events extend well beyond the immediate toll of accidents and equipment failures. As climate change increases the frequency of extreme weather events that can destabilize power grids, and as the population ages, the public health burden of blackouts is likely to grow.
“These findings highlight the underestimated health burden of blackouts and the need for improved preparedness in a changing climate,” the authors write. For the more than 50 million people affected by the 2025 blackout, and for the many millions more who live in grids vulnerable to similar failures, the study is a reminder that the true cost of a power outage is not counted in the immediate reports.
Sources
[1] Konstantinoudis, G. and Riou, J. “Excess mortality attributable to the 2025 Iberian Peninsula blackout.” Nature Communications, 20 July 2026. DOI: 10.1038/s41467-026-75581-w. https://www.nature.com/articles/s41467-026-75581-w
[2] Garcia-Garcia, D., et al. “Exploring all-cause mortality surveillance during the Iberian Peninsula power outage, Spain, 28 April 2025.” Eurosurveillance, 2025; 30(26): 2500405. DOI: 10.2807/1560-7917.ES.2025.30.26.2500405