Researchers have found that about a quarter of the fires caused by lightning that grow to more than 4 km² (988 acres) are reported more than a week after they are ignited.
A paper published in the Fire Open Access Journal describes how the National Lightning Detection Network (NLDN) and U.S. Forest Service fire data were used to determine the correlation between lightning strikes and the reported location of lightning-caused wildfires.
The NLDN, which has been used operationally for several decades, consists of 113 sensors across the continental United States and has a reported flash detection efficiency of cloud to ground flashes between 90–95%, with spatial errors that are typically less than 500 meters for the flash data used in the study.
The researchers found, of lightning-caused fires that grew to more than 4 km² (988 acres):
50% reported the same day 71% reported within 3 days 73% reported within 5 days 77% reported within 7 days
Holdover fires that are not reported for days or weeks after the lightning occurs can be problematic for land managers. Shortly after a thunderstorm has left the area, fire detection efforts are often ramped up and may continue in that mode for a few days. Fires that smolder in duff or under snow and suddenly grow can be unexpected. Firefighting resources that may have been staged in anticipation of emerging fires could be released or assigned to active incidents, complicating efforts at quick initial attack with overwhelming force.
Authors of the paper: Christopher J. Schultz, Nicholas J. Nauslar, J. Brent Wachter, Christopher R. Hain, and Jordan R. Bell.
Scott Gorman, the crew superintendent on a California hotshot crew, was interviewed on National Public Radio along with his wife Sarah Barnes. They talked about how the partial government shutdown is affecting their family, and the time that Mr. Gorman and three other firefighters were struck by lightning while working on the Noon Fire in Arizona in 2004.
The interview was posted by NPR on January 21, 2019.
During a 21-year period 84 percent of the wildfires in the United States were caused by humans, but the ratio varies greatly across the country.
A study published by the National Academy of Sciences looked at the causes of wildland fires, human vs. lightning, and their occurrence geographically and seasonally. The researchers analyzed 1.5 million fire occurrence records from 1992 to 2012.
I was interested in reading the paper after having been attracted to the compelling graphics comparing the numbers of fires caused by humans and lighting, ecoregion by ecoregion over time.
The research was conducted by Jennifer K. Balch, Bethany A. Bradley, John T. Abatzogloue, R. Chelsea Nagy, Emily J. Fusco, and Adam L. Mahood.
You might have noticed a large short-lived spike in the number of human caused fires in several of the ecoregions around June-July. That represents ignitions caused by fireworks on the Fourth of July.
Below is an excerpt from the research:
“In conclusion, we demonstrate the remarkable influence that humans have on modern United States wildfire regimes through changes in the spatial and seasonal distribution of ignitions. Although considerable fire research in the United States has rightly focused on increased fire activity (e.g., larger fires and more area burned) because of climate change, we demonstrate that the expanded fire niche as a result of human-related ignitions is equally profound. Moreover, the convergence of warming trends and expanded ignition pressure from people is increasing the number of large human-caused wildfires. Currently, humans are extending the fire niche into conditions that are less conducive to fire activity, including regions and seasons with wetter fuels and higher biomass.
“Land-use practices, such as clearing and logging, may also be creating an abundance of drier fuels, potentially leading to larger fires even under historically wetter conditions. Additionally, projected climate warming is expected to lower fuel moisture and create more frequent weather conditions conducive to fire ignition and spread, and earlier springs attributed to climate change are leading to accelerated phenology. Although plant physiological responses to rising CO2 may reduce some drought stress, climate change will likely lead to faster desiccation of fuels and increased risk in areas where human ignitions are prevalent.”
In spite of the weather forecast, the lightning predicted for Southwest Oregon on Sunday didn’t really pan out, but portions of other western states received thousands of strikes. Firefighters may have some followup to do in Northeast Montana, Southwest Wyoming, Utah, Colorado, Nevada, the Sierras in California, and states in the Great Plains.
During the rest of this week Southern California will likely experience temperatures much higher than normal, possibly setting a few daily records. Weak hot and dry sundowner winds could occur near Santa Barbara bringing compressional heating and high fire danger.
Here’s more weather information from the National Interagency Fire Center, issued July 23:
A critical fire weather scenario will begin to set up as shards of monsoonal moisture begin to filter further into the Pacific Northwest and the Northern Rockies. These storms, while still isolated, will be dry and should trigger new starts as the stage begins to set for the next few days after [Monday], which should be pretty convective.
The National Weather Service is describing the lightning that is in the forecast for south-central Oregon and extreme northern California as “abundant”. It should begin by early Sunday afternoon and continue into the evening.
Lightning is also predicted for southwest Idaho and northern Nevada. There could be wetting rain with the thunderstorms except in Nevada, where dry strikes could occur. All of these areas are under a Red Flag Warning Sunday.
Some land managers in Oregon have brought in additional firefighting resources to assist in initial attack of any new lightning-caused fires.
(Originally published at 1:33 p.m. MDT September 11, 2017)
Jeff Zimmerman took these photos September 10 and sent them to us today. Here is how he described the event.
From the deserts to the sea, a wonderful display of lightning. Off the coast near Avalon where hundreds of strikes were recorded with numerous strikes all the way to Tehachapi Mountains. Tejon Ranch and Highway 58 area was bathed in lightning too. A new fire was reported on the Los Padres National Forest, lightning strike near Chuchapate (Sawmill). Possibly a few more isolated storms today, followed by gusty NW winds later this week. The first Santa Ana may set up when snow comes to Montana and offshore flow begins later this week bringing critical fire weather with it. Attached are a few shots from the desert in Neenach, CA (map).