New CU Boulder-led research shows that three major 鈥渟witches鈥� affecting wildfire鈥攆uel, aridity听and ignition鈥攚ere either flipped on and/or kept on longer than expected last year, triggering one of the largest and costliest U.S. wildfire seasons in recent decades.
The 2017 wildfire season cost the United States more than $18 billion in damage. That year, 71,000 wildfires scorched 10 million acres of land, destroying 12,000 homes, evacuating 200,000 people and claiming 66 lives. By comparison, 2016 saw 5.4 million acres burned.
鈥淟ast year, we saw a pile-on of extreme events across large portions of the western U.S: the wettest winter, the hottest summer and the driest fall鈥攁ll helping to promote wildfires,鈥� said lead study author Jennifer Balch, director of CU Boulder鈥檚 Earth Lab in the听.
罢丑别听听co-authored by researchers at CU Boulder鈥檚听Institute of Arctic and Alpine Research (INSTAAR), Columbia University and the University of Idaho听was published today in the journal听Fire.
Western wildfire seasons are worse when conditions are dry and fuel-rich, raising the chances of ignition. Climate change likely exacerbates fuels and dryness, the paper found, and human behavior contributed the sparks. The research team sought to pinpoint the precursors that led to 2017鈥檚 fires in order to provide information for decision makers considering policies that might prevent or minimize future fire disasters.听
2017鈥檚 wet winter acted as the first trigger. Increased precipitation early in the year fed the growth of fine grasses across the western United States鈥攇rasses that would later serve as fuel for fire. Then, summer and fall brought dry, arid conditions, baking the dense fields of grasses into dehydrated kindling.
The scene was set for the third switch: ignition. Nearly 90 percent of total wildfires last year were sparked by people; Balch鈥檚听previous work听has illuminated just how extensively humans exacerbate wildfire. Human activity triples the length of the average fire season.
鈥漌e expect to see more fire seasons like we saw last year,鈥澨齭aid Megan Cattau, an Earth Lab researcher and a co-author on the study. 鈥淭hus, it is becoming increasingly critical that we strengthen our wildfire prediction and warning systems, support suppression and recovery efforts and develop sustained policies that help us coexist with fire.鈥�
The paper notes that computer climate models project an increased risk of extreme wet winters in California and a decrease in summer precipitation across the entire West Coast. Those models also tend to project a delay in the onset of fall rain and snow.
Although naturally occurring climate variability influences environmental conditions that affect the wildfire season, that variation is superimposed on an anthropogenically warmer world, so climate change is magnifying the effects of heat and precipitation extremes, Balch said.听
鈥淭he 2018 wildfire season is already underway and here at home in the southern Rockies, fuels are very dry,鈥� said Balch. 鈥淛une is forecasted to be a busy month in terms of wildfires due to severe drought and low snowpack.鈥澨�
