It’s late August 2019, and plenty of news outlets are reporting forest fires in the Amazon rainforest. The news stories revolve around two points; one, that the fires are of an unprecedented scale, and two, that the policies of Brazil’s president, Jair Bolsonaro, are to blame for the increase in deliberate fires created by farmers and loggers. A particular amount of attention is being paid to the number of fires within Brazil, with statements such as:

Amazon wildfires at record numbers, says Brazil’s space centre

The Irish Times

This year has seen more than double the number of fires in Brazil than in 2013

BBC News

But is the number of fires truly exceptional in 2019? Forest fires, deliberate or otherwise, are a feature of tropical rainforests during the dry season. We expect a certain number of fires to occur with cyclical regularity. However, if the number or extent of the fires exceeds our expectations, this would be cause for concern. Let us look at the data.

The National Institute for Space Research of Brazil (INPE) maintains a public database of forest fires detected through satellite imagery across South America. Focusing on Brazil alone, we can look at historical data for the number of active fires for each month. We see that forest fires have a seasonal effect, with a spike during the dry season of July to October, as well as year-on-year variation.

With this historical view, 2019 does not seem to stand out; however, we do not yet have data for September, the most active month for fires in Brazil. Let us look instead at the cumulative number of active fires in each year, leading up to the month August.

Here we see that 2019 has had an unusually large number of fires so far, compared to the same point in the previous two years, but it is still lower than for the 2002-2007 period, where many more fires were reported by this point in the year. We might reasonably ask if the forest fires in August 2019, while unusually numerous, fall within the normal variation of fires reported for equivalent August periods in previous records.

We can answer that question by looking at the expected range (confidence interval) of the number of fires for any given August. For the 20-year span up to 2018, we can say that 95% of the time, there were between 36,000 and 57,000 active fires on any given August. For the current year, that value is presently at 36,785. This number will likely rise, as they are 8 days still left in August, but when assessed in this fashion, 2019 is not a statistical outlier.

What are we to conclude? Are the forest fires in Brazil exceptional this year? Perhaps in scope or intensity, but when considering the number of individual fires alone, it is not. The records so far shows an increase compared to the previous two years, but it is not abnormal within the range of forest fires reported over the past two decades. Are forest fires going to get worse? In the immediate future – yes. September is historically the month with the largest number of fires in Brazil, so we are likely to continue to see the Amazon in the headlines.

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Satellite imagery data is provided by Instituto Nacional de Pesquisas Espaciais (INPE) of the Brazilian Ministry of Science, Technology and Innovation. For full details on methodology, see their wildfire database and documentation.