Did the weather fuel climate-changing forest fires in the Amazon in 2019?

12 Mar 2021 01:24 PM

In 2019 there was a sudden spike in Amazon fires that captured the world’s media attention. Between them the blazes destroyed 906,000 hectares of rainforest – an area larger than the island of Corsica.

In their natural state the forests of the Amazon draw down atmospheric carbon, but during fires this carbon is released to the atmosphere. Pic: Shutterstock.

The thousands of fires produced around 400 million tonnes of carbon emissions adding to the atmospheric concentration of greenhouse gases and exposing millions of people to increased air pollution, including the residents of São Paulo, 1,700 miles away.

With an increase of carbon emissions up by 80 per cent on the previous year, a team of scientists led by the UK Centre for Ecology & Hydrology and the Met Office began a research study to discover if meteorological conditions could account for the fire surge during the year.

The team examined data on land use, population density, rainfall patterns, humidity, temperature and lightning to build a picture of the likelihood that factors related to weather conditions may have fuelled the increase. The team’s results indicated that 2019 was not an unusual year meteorologically and this led to the startling finding that there was only a seven per cent chance that weather conditions triggered the increase in fires in the main deforested areas of the Amazon between June and August.

Figure 1. Maps of observed percentage of burnt area.
Left: Observed burnt area, for June–August 2002–2019 annual average.
Right: Difference between June–August 2019 and 2002–2019 average.

A key aspect of the research was comparing meteorological conditions for any given year with the extent of burned areas, following forest fires. A significant finding was that observations show that the burnt area was higher in 2019 than in previous years in regions where there had already been substantial deforestation.

Although fires can start from natural sources of ignition within the Amazon, previous studies have shown that fires in the region are rarely ignited without human intervention. The humid rainforest vegetation is not adapted to frequent burning and consequently there is higher tree mortality when fires do occur.

“Our conclusion is that human activity – landscape changes or fires started to clear forest – caused the increased level of burning and not the weather,” says Dr Doug Kelley of UKCEH, who led the research.

Dr Kelley added living trees hold water, and this can suppress the spread of wild fires, even in drought periods. However, in deforested areas, felled wood and vegetation may be drier, acting as fuel for a fire.

The pied tamarin is one of the world’s most threatened primates. Confined to a small part of the Brazilian Amazon rainforest, the Critically Endangered monkey is affected by several factors, largely linked to deforestation. Picture: Shutterstock

The Amazon is crucial to regulating the world’s climate as it absorbs large amounts of carbon dioxide (CO2) from the atmosphere. However, being a significant store of carbon, this may be re-released as CO2 during deforestation and burning.

The scientists say deforestation creates a series of vicious cycles. It reduces the Amazon’s ability to store carbon and absorb CO2 while also increasing the risk of wildfires, which emit greenhouse gases and damage plant life that would otherwise retain carbon and remove CO2 from the atmosphere. While the Amazon ecosystem ‘takes care of itself’ by recycling its own water, deforestation will reduce its ability to do this, and make the rainforest less stable.

Met Office climate scientist Dr Chantelle Burton, a co-author of the study, says:

“It is important to be able to understand what is driving changes in fire trends, especially in globally important carbon sinks such as the Amazon. This could help inform decision making around land management practices to minimise unintended impacts – both on short timescales and for future responses to climate change.”

The study – Low meteorological influence found in 2019 Amazonia fires -was funded by the Natural Environment Research Council. It has been published in the journal Biogeosciences.