Climate Change and Lengthening Fire Seasons

A widely cited 2015 study by Matthew Jolly and colleagues, published in Nature Communications, analyzed global weather data from 1979 to 2013 and found that the length of the fire weather season, the period each year when conditions are conducive to fire ignition and spread, had increased by an average of about 18.7 percent worldwide over that period, with the largest increases documented across parts of the western United States, the Mediterranean Basin, and East Africa. The study attributed this lengthening primarily to rising temperatures and increased "vapor pressure deficit," a measure of the atmosphere's drying power that determines how quickly vegetation and dead fuel lose moisture, along with earlier spring snowmelt in temperate and mountainous regions, which extends the window during which fuels are dry enough to sustain fire.