916 Million People a Year Meet a Heatwave and Fire Smoke on the Same Day

A study published Oct. 14, 2026, in Science Advances counts how often people get a heatwave and smoke from landscape fires in the same place on the same day. Yao Wu of Peking University, Yuming Guo of Monash University and colleagues report that 916 million people a year had at least one such day between 2000 and 2019.

The authors say the study is meant to supply high-resolution data for health impact assessments and to help decide where mitigation and adaptation efforts should go. What it counts is days of overlap, not illness: deaths, hospital visits and other health outcomes are not part of it.

The paper reports that 55.9% of the world's population lives where that overlap grew over the two decades. Average exposure rose from 1.0 day per person a year in the first of the two decades to 1.7 days in the second. Of the overall rise in exposure, the researchers attribute 70.5% to the exposure itself becoming more intense and the rest to population growth. The analysis ends with that window, so the figures are a measured history and not a current rate.

Countries with a low human development index, the lower end of a standard scale of income, health and schooling, recorded both the most overlap days per person and the largest increases.

In the paper's own framing, landscape fires increasingly threaten public health through the air pollution they produce, and the risk is amplified during a heatwave. The work was funded by the Australian Research Council, the National Natural Science Foundation of China and Australia's National Health and Medical Research Council, among others.