Fire Seasons Becoming Longer and More Frequent

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New analysis of past fire seasons have shown that the average lengths of fire seasons around the world have actually grown longer. The meteorological data spanning 35 years was analyzed by ecologists working with the U.S. Forest Service and comprised of a variety of weather factors that contribute to longer, dryer seasons.

In the years between 1979 and 2014, four ecological and meteorological factors were taken into consideration which included temperature, humidity, precipitation, and wind. Each one of these factors was compared with the others to see how each one individually influenced the strength of wildfires, and how different conditions together had an effect on the fires.


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Fire season itself is determined by specific location; for example, wildfire season in California is much different than it is in Eastern Washington or Mexico. The beginning and end of a fire season can be dramatically different depending on location. Between the years 1996-2013 longer fire weather seasons were recorded as opposed to the years between 1979-1996.

The research on fire seasons indicated that around 25% of Earth’s vegetated surfaces now experience a longer fire season. The length of the fire season didn’t extend overnight- it was a slow and gradual change that encompassed weather patterns and climate shifts as well. In parts of the Western U.S., Mexico, Brazil and East Africa the fire season is nearly one month longer than it was 35 years ago.

Changes in fire season length from 1979 to 2013.  Map by Joshua Stevens, using data provided by Matt Jolly, USDA Forest Service.
Changes in fire season length from 1979 to 2013. Map by Joshua Stevens, using data provided by Matt Jolly, USDA Forest Service.

Global warming and climate change contribute to some of the meteorological and weather conditions that make fire seasons longer. The lack of precipitation over a year affects water levels, ground saturation and also can link together multiple days of no precipitation at all. This can lead to dryer ground, more dead underbrush underfoot, and more kindling that a wildfire could burn through when the conditions are right. However, areas of Western Africa and South America have experienced a higher than average amount of rainfall and an easing of fire risks.

Some locations might not be experiencing longer fire seasons, but more frequent fire seasons. This trend is concerning as it puts more homes and land at risk of destruction over a longer period of time during the year. Companies, families and those who depend on the land for their jobs experience a higher level of worry and stress when the land they need to survive is under threat of fire.

The study doesn’t have the ability to indicate how many acres of land were affected by wildfires or how intensely the fires burned over the affected land. Additionally, there isn’t any room for man-made or naturally occurring wildfires that may increase the length or frequency of wildfires in a specific location. However, the report is valuable in its global wildfire data and the factors that influence their dangerous increase.

References

Jolly, M. et al, (2015, July 14) Climate-induced variations in global wildfire danger from 1979 to 2013. Nature Communications, (6) 7537.

Longer, More Frequent Fire Seasons.  July 28, 2015.  NASA


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