Global Wildfire Danger Increases Caused By Climate Change

20 07 2015

Another guest post from Mark Cochrane

In a recent paper in Nature Communications, Jolly et al (2015) report on “Climate-induced variations in global wildfire danger from 1979-2013”.

Climate strongly influences global wildfire activity, and recent wildfire surges may signal fire weather-induced pyrogeographic shifts. Here we use three daily global climate data sets and three fire danger indices to develop a simple annual metric of fire weather season length, and map spatio-temporal trends from 1979 to 2013. We show that fire weather seasons have lengthened across 29.6millionkm(25.3%) of the Earth’s vegetated surface, resulting in an 18.7% increase in global mean fire weather season length. We also show a doubling (108.1% increase) of global burnable area affected by long fire weather seasons (>1.0 σ above the historical mean) and an increased global frequency of long fire weather seasons across 62.4millionkm2 (53.4%) during the second half of the study period. If these fire weather changes are coupled with ignition sources and available fuel, they could markedly impact global ecosystems, societies, economies and climate. (full paper)

If you prefer lighter reading, here is an article reporting on the work

Wildfires Are Happening More Often and in More Places

Average fire season length has increased by nearly a fifth in the last 35 years, and the area impacted has doubled

What this paper basically shows is that conditions are getting drier for longer periods of time in regions that currently have burnable vegetation. This doesn’t necessarily mean that we will have more wildfires but it certainly sets the seen for worse ones. Some places are getting better conditions but many more are getting worse conditions for possible wildfires. If the climate were stable you would expect there to be a rough balance between the area of places getting milder and those getting more toasty. This is definitely not the case (Figure a – below). On top of this, the frequency with which very long fire seasons (basically extended severe dry periods) are occurring across the Earth is increasing, more than doubling in the last 35 years (Figure b – below). Any place that is red on either map is at risk for more extensive or severe wildfires. Being red on both maps is not a recipe for ecological happiness…

Full disclosure, this is actually my own research, I’m the second author. The work was funded by NASA as part of one of my research grants. It may not look like much but it represents four years of work crunching lots of numbers into usable form that could then be analyzed and interpreted. Science in action (sometimes feels like inaction).


a shows areas with significant trends in fire weather season length from 1979 to 2013. b shows regions that have experienced changes in the frequency of long fire weather seasons (>1σ above historical mean) during the second half of the study period (1996–2013) compared with the number of events observed during the first half (1979–1996). Areas with little or no burnable vegetation are shown in grey (NB) and NC indicates areas with no significant change. Reds indicate areas where fire weather seasons have lengthened or long fire weather seasons have become more frequent. Blues indicate areas where fire weather seasons have shortened or long fire weather seasons have become less frequent.