Smoking out the full impact of wildfires

Smoking out the full impact of wildfires
By Nicole Lim, Senior editor

Credit: iStock.com / GomezDavid

What happens to the body under extreme circumstances used to worry mainly exercise physiologists. But as desert-like temperatures become common well beyond the boundaries of the Sahara, heat injuries are a looming health concern. And it is not just the thermostat that’s triggering red health warnings.

With extreme heat waves now five times more likely to occur than 150 years ago, the risk of other extreme events such as wildfires has also risen, displacing thousands of people and causing direct harm to health. While studies of individual wildfire events have documented the immediate health impact, what remains less clear is the full extent of the health risks both for people near the source of the fire and communities far downwind.

To answer these questions, a multidisciplinary team of scientists from around the world set out to build a model that will allow health officials and policymakers to predict the impact of wildfires anywhere in the world on their communities.

“The whole aim of this is to develop an exposure-response function between exposure to particulate matter from wildfires and specific health outcomes,” said anaesthesiologist Fintan Hughes from Duke’s School of Medicine, who is a co-lead of the project, which also includes other teams from Duke University as well as collaborators in Brazil, Singapore and the UK.

“The whole aim of this is to develop an exposure-response function between exposure to particulate matter from wildfires and specific health outcomes.”
Fintan Hughes

Using a range of environmental data sources including data from GEOS-Chem, a global 3D model of atmospheric chemistry that is driven by meteorological inputs from NASA’s Goddard Earth Observing System, the Duke team has painstakingly extracted PM_2.5 measurements that are attributable to wildfire smoke in the Americas and South East Asia from 2018 to 2022. PM_2.5 refers to fine inhalable particulate matter of 2.5 microns or less in diameter. That is a fraction the width of a human hair.

With the extracted readings in hand, the team is now mapping health outcome data against these readings, starting with Brazil, whose national electronic health records capture about 80 per cent of the population’s health data.

“So, the health outcomes we’re looking at are cardiac events, like myocardial infarctions, exacerbation of arrhythmias, stroke, heart attacks. Then from the respiratory side, things like asthma and COPD exacerbations as well as a combination of obstetric and neonatal outcomes, such as rates of pre-eclampsia, premature births, low birth weight,” listed Hughes.

The Singapore team from Duke-NUS’ Pre-hospital and Emergency Research Centre, meanwhile, is applying an approach similar to the Duke team to extract measurements of PM_2.5 concentrations attributable to haze and land fires from local data.

One unique challenge that the Singapore researchers are facing is that the grid size used by the GEOS-Chem model to track atmospheric conditions is better suited to larger cities and areas. “We are discussing whether regionally estimated land fire fractions can be applied to derive PM_2.5 concentrations at finer spatial grids,” said environmental epidemiologist Joel Aik, who’s an adjunct assistant professor with the Centre.

Once the PM_2.5 concentrations attributable to land fires have been isolated, the team will be able to quantify the resulting health burden.

“This finer resolution analysis enables us to determine which areas are more likely to carry a higher health burden during periods of haze and help inform the allocation of additional resources for health services in those specific areas,” added Aik.

Credit: iStock.com / abinda muchlas barru

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The Singapore analysis will be pooled with the inputs from collaborators in other countries to contribute to a global model.

“We’re doing this across several different countries, so that we’ll have something that’s internationally generalisable,” confirmed Hughes.

Using a non-linear modelling approach, the team hopes to shed light on the relationship between observed health outcome and wildfire smoke, particularly when concentration of particulate matter reaches extreme levels.

“There’s a lot of studies that say for a heart attack, there’s an increased odds ratio of say 1.2 for every 10 microgrammes per metre cubed of PM_2.5, which assumes an entirely linear relationship. But it tells you less about what’s going to happen when you have really high concentrations,” he explained, noting that the relationship could become exponential after breaching a certain threshold.

As well as considering the spatial aspect of the relationship between wildfire smoke and health outcome, the team is also investigating the impact when accounting for social determinants of health.

This multidimensional approach to teasing out the impact of wildfire smoke on communities will help advance public health planning and advocacy, including efforts such as the Lancet Countdown, which tracks progress on health and climate change. Currently, the Lancet Countdown relies on proximity to fires to track the number of people affected by wildfires.

“We can improve that model so that instead of just saying how many people are exposed we can say what the impact of this exposure is,” said Hughes. “And that is the purpose of our work. It lets us understand that while we have increasing wildfire exposure and increased wildfire frequency, when people get exposed what does it actually do.”

The project is funded by a Duke University grant and will complete in 2025.