Wildfire risk in California no longer linked to winter precipitation
Lead author Eugene R. Wahl of the National Oceanic and Atmospheric Administration said, “The method we used to determine the average winter jet stream conditions is a real advance. Coupled with independent precipitation and fire records, this is a state-of-the-art coupling of paleoclimate and paleoecology.”
The study is the first to show the close connection between winter precipitation in California and the position of the jet stream back to the year 1571, Trouet said. The study is also the first to examine the relationship of past winter precipitation, the position of the jet stream and past fire activity stretching back to 1600, she said.
As part of a larger project to extend global reconstructions of temperature, precipitation and atmospheric circulation further into the past, Wahl and Zorita were figuring out how the North Pacific jet stream affected precipitation in California for centuries. Wahl, a paleoclimatologist at NOAA’s National Centers for Environmental Information in Boulder, Colorado, was a co-leader for the North America part of the larger project.
Trouet and Taylor of Penn State in University Park, Pennsylvania, had already reconstructed California’s fire history back to 1600, and Trouet had reconstructed the behavior of the North Atlantic jet stream back to 1725.
After Wahl heard Trouet give a presentation about her North Atlantic jet stream research, the four scientists joined forces to see whether there were links between the past behavior of the North Pacific jet stream and California’s fire and precipitation history.
“When the jet stream is positioned over California, it’s like a fire hose–it brings storms and moisture straight over California,” Trouet said. “What we see post-1900 is that the position of the jet stream is still an important driver of moisture to California–it brings moisture to California when it’s in the right position–but there’s a disconnect with fire.”
The likelihood that every year may be a high-fire year will be a significant societal challenge, Taylor said.
“Fire not being influenced by moisture anymore? That is surprising. It’s going to be a problem for people, for firefighters, for society,” he said. “The only thing we can control is fuels, so what it suggests is that we take that very seriously.
“The last three years may be a harbinger of things to come,” he said. “Between 1600 and 1903 there was not a single case of a high-precipitation year coupled with a high-fire year as occurred in 2017.”
The research team’s next step is to expand this research to see how the jet stream patterns correspond with fire in other types of forested ecosystems farther north.
— Read more in Eugene R. Wahl et al., “Jet stream dynamics, hydroclimate, and fire in California from 1600 CE to present,” Proceedings of the National Academy of Sciences (4 March 2019) (DOI: 10.1073/pnas.1815292116)
