In the western United States, wildfires destroyed an average of 13,500 square kilometers per year between 2001 and 2018, more than double the 1984-2000 period. “It happened faster than we expected,” Rong Fu, a climate expert at UCLA University of California, told the Los Angeles Times. The meteorologist is leading the study, which was published Monday in the scientific journal PNAS (Proceedings of the National Academy of Sciences of the United States).
To understand what is the basis of this rapid degradation, Fu’s team analyzed various factors that work in ‘vapor pressure deficiency’, which refers to air drought. VPD refers to the difference between the amount of water in the atmosphere and the maximum that the atmosphere can hold. With high scarcity, air will absorb water from the soil and plants. This leads to conditions that promote fire.
Scientists have found that the increase in wildfires in the western United States is proportional to the increase in VPD during the hot season. The study says the number of days with high VPD has almost doubled in the 2011-2018 period compared to the previous period.
Fu and his colleagues calculated that only one-third of the average worsening of VPD was due to ‘natural’ atmospheric changes. The remaining, more than two-thirds, are largely the result of human activity, due to climate change over the past twenty years.
“Before 2000, classical weather models allowed us to describe the weather that triggered wildfires,” Rong Fu told the LA Times. But not anymore. In fact, according to some models in the study, man-induced climate change may account for nearly 90 percent of VPD anomalies.
In August 2020, when the California region was hit by the largest fire, man-made climate change accounted for almost half of the “exceptionally high” vapor pressure deficit, the study concludes. The wildfire burned about 4,200 square kilometers.