A team of researchers led by Bois State University (United States) has shown that human exposure to wildfires increased by 40 percent worldwide between 2002 and 2021, even though the area burned decreased by 26 percent over the same period.
The study, published in the journal Science, concluded that the increase in this exposure is related to the population growth in the wildland-urban interface, and showed that these types of dynamics account for 25 percent of the 440 million people exposed to fires.
"Wildfires are increasingly destructive to people and property globally as a result of increased fire activity and human development at the wildland-urban interface (…) Almost all of the increase in exposure has been recorded in Africa, which accounted for more than 85 percent of all people directly exposed to wildfires during the study period," the article reads.
The study also found increases in the Americas and Asia, although to a lesser extent than in Africa, while no increases were found in Europe and Oceania.
The research also found that wildfires, defined as those occurring in vegetated areas and excluding commercial agricultural areas, are directly responsible for at least 2,500 human deaths and 10,500 injuries between 1990 and 2021, while indirectly causing 1.53 million deaths annually worldwide as a result of the air pollution they cause.
Although researchers have "directly" linked fire activity to climate change, which they attribute to the increase in the number of days favorable for "extreme fire behavior" in fire-prone regions, they have noted that human activity can exacerbate the impacts of climate change.
In fact, they have emphasized that human-caused fires, both intentionally and accidentally, account for 84 percent of all wildfires in the United States and 90 percent in Mediterranean Europe.
While lightning ignitions may be prevalent in more remote regions, scientists have insisted that human activity "enormously" alters the timing and location of fires.
They cited as an example the introduction of invasive species in the North American deserts, which ultimately resulted in "more frequent and larger" wildfires, while agriculturally induced land fragmentation in the African savannah has reduced burned areas.
This latter practice is one of the main reasons for the decrease in burned area, despite the increase in the extent of fires in temperate and boreal forests, and the greater tendency toward intense fires.
The research used 18.6 million individual fire records from 2002 to 2021 from the Global Fire Atlas, based on MODIS and gridded population data from WorldPop. They also used MODIS-based land-use and land-cover data, active fire records, and vegetation indices to exclude non-wildfires.
The article acknowledges that, although human exposure to wildfires has been defined as the number of people living within burned areas, their effects extend "well beyond" these territories.
EXPERTS DIFFER ON THE QUALITY OF WORK
This research has generated differing opinions among experts consulted by SMC Spain. Víctor Fernández-García, a professor in the Department of Agricultural Engineering and Sciences at the University of León, emphasized that the study's approach is "novel" in focusing on fire exposure and differentiating between the role played by population dynamics and changes in fires in the evolution of this exposure.
"The article offers robust and well-founded results, considering the limitations inherent in using moderate spatial resolution data (...) The main novelty of the work lies in demonstrating that there is a global increase in fire exposure, and that this increase is mainly due to population growth and redistribution in fire-prone areas," he added.
Meanwhile, Cristina Montiel Molina, professor of Regional Geographic Analysis and director of the "Forest Geography, Policy, and Socioeconomics" Research Group at the Complutense University of Madrid, has stated that the article presents "several serious deficiencies," such as the fact that it identifies exposure with urban-wildland interfaces.
"Human exposure to fires is much broader; it's not limited to these at-risk areas. Secondly, it treats wildland-urban interfaces generically, which is incorrect given the wide variety of cases. Furthermore, it doesn't even define or delimit the general term used in the article," he stated.
He also criticized the fact that these territories are treated equally on all continents, an approach he considers "uncertain" given the different territorial dynamics.
"The article also lacks methodological rigor in its handling of space-time scales. It also fails to specify the sources of information it uses. The comparative analysis and the results it presents are inconsistent. The conclusions lack scientific basis and make no serious contributions," he concluded.
For his part, José Valentín Roces, assistant professor in the Department of Organismal and Systems Biology at the Joint Institute for Biodiversity Research (IMIB) of the CSIC-University of Oviedo-Government of the Principality of Asturias, praised the "high quality and impact" of the study for connecting changes in fires and population.
"Their results are conclusive: since the beginning of the 21st century, the number of people directly exposed to forest fires, particularly the most intense ones, has continued to grow. This spatial coincidence between fires and human settlements is evident on all continents, although with different magnitudes and explanatory factors. In some regions, population growth has been a determining factor, while in others, climatic factors have predominated," he concluded.
