COVID-19 lockdowns cut global active-fire detections by 12.3% in early 2020, Cell Reports Sustainability study
Satellite data for the first half of 2020 show 12.3% fewer active-fire detections under COVID-19 restrictions. Forests fell most, while some countries saw more fires.
A team led by Jianghao Wang of the Chinese Academy of Sciences used the drop in human activity during the COVID-19 pandemic as a natural experiment to separate human influence on fire. The study was published in Cell Reports Sustainability. Comparing the first half of 2020 with historical baselines, the authors found an average global decline of 12.3% in fire incidence sciencedirect.com
Cell Reports Sustainabilitysciencedirect.comOpen source ↗. The decline varied strongly from region to region.
Method: satellite detections and mobility data
The researchers defined the periods of restricted mobility from regional lockdown orders and mobile phone location data. Fires were tracked with the VIIRS sensor on the Suomi NPP satellite, which detects heat signatures at 375 m resolution. Each hot spot counts as one active-fire detection, so a single large fire can appear as several. The sensor does not distinguish wildfires from prescribed burns, so the intent behind each fire is unknown.
Detections during the 2020 restriction periods were compared with the same weeks in 2013–2019, with weather differences taken into account. Without the weather adjustment the drop was 5.8% and not statistically significant. After adjustment the estimate rose to 12.3%.
Results: forests down, some countries up
Fires in forests decreased by about 27.7% and in grasslands by 8.4%. Shrublands, savannas and croplands showed little difference. The authors read this as evidence that humans are a major cause of fires in forests and grasslands sciencedirect.com
Cell Reports Sustainabilitysciencedirect.comOpen source ↗.
Wang stressed that 12.3% is a net effect, not the share of fires caused by humans, because ignition and suppression changed in opposite directions. Most of South America, southern Africa and northeast Asia saw more fires during lockdowns, including 31.4% in Colombia, 25.4% in India and 70.7% in Honduras. No direct field data explain this. The authors infer weaker fire suppression, which Wang called "an inference, not a direct observation".
In 12 countries with records of prescribed burning, the burned area in 2020 was about half the 2013–2019 average. When prescribed-burn areas were excluded, the decline in those countries shrank from 45.3% to 27.8%.
The study has limits. Mobile phone data may miss human activity in rural areas with poor coverage. The analysis covered only the first half of each year, so regions where fires peak later, such as the western US, may be underrepresented.
