A Quiet But Deadly 2013 U.S. Fire Season

It was an unexpectedly quiet and deadly year for wildfires in the U.S. in 2013. The 4.2 million acres burned ranked as the 2nd lowest amount in the past ten years, according to the National Interagency Fire Center (NIFC.) The total number of wildfires was just over 43,100, which was well below the ten-year average of about 68,000 fires, and the lowest number since accurate record keeping began in the early 1980s. According to meteorologist Steve Bowen of Aon Benfield in an interview with USA Today, total wildfire economic damages during the year were approximately $700 million, or 46% below the 10-year average of $1.3 billion. However, 2013 was the third deadliest wildfire season for firefighters since records began in 1910, with 34 firefighters perishing.





The deadly Yarnell Hill, Arizona fire
On June 30, 2013, the third deadliest wildfire in U.S. history, Arizona's Yarnell Hill Fire, took the lives of 19 firefighters with the Prescott Fire Department's interagency Granite Mountain Hotshots. Close watch was on the weather during the fire, as temperatures hit 100° and winds gusted over 20 mph. However, a line of thunderstorms caused winds to increase and shift, gusting to over 40 mph, and changing direction from west-southwest to north-northeast. This rapid change in the winds caught the firefighters off guard, allowing the fire to quickly grow from 300 acres to 2,000 acres. It was this wind event with persistent hot temperatures and dry surface conditions that caused the erratic wildfire behavior and killed the 19 out of 20 Hotshots crew.


Video 1. The June 30, 2013 Yarnell Hill Fire in Arizona as seen from the air.


Figure 1. The Yarnell Hill Fire was the third deadliest wildfire in U.S. history. Image credit: ecowest.org.

Didn't they say something about a record-breaking fire year? What happened?!
During the winter of 2012 and 2013, the nation was in the worst drought conditions since 2000 due to below normal snow pack across the West, according to the US Drought Monitor. The snowfall maps below show the percent of average snow pack over the Four Corners and Great Basin, respectively, measured April 1st, 2013 by the NRCS.





The chart below shows percent of drought conditions across the Contiguous U.S, with Exceptional Drought in dark red, Extreme Drought in red, Severe Drought in orange, Moderate Drought in tan, and Abnormally Dry in yellow.



As you can see from this chart, we started off 2013 at nearly the driest conditions across the U.S. since 2000, with nearly 80% of the country abnormally dry and over 6% in exceptional drought conditions. Due to the dry conditions, fire management agencies were expecting an exceptionally active fire season, since dry conditions in 2011 and 2012 caused historic fire years. (For example, the massive Wallow Fire in 2011 burned 538,000 acres in AZ and NM; the Whitewater-Baldy fire in 2012 was the largest single fire in New Mexico's history, at 297,845 acres; and the devastating 2012 Waldo Canyon Fire in Colorado was the most destructive fire in state history, with 346 homes burned.)

So what happened? During the summer of 2013, the Southwest benefited from a much wetter and more active monsoon season than in previous two years, which led to one of their wettest summers on record. For example, Colorado and the Four Corners reported record to near record wet conditions from July - November. Additionally, an active weather pattern across the Southeast U.S. brought near record wet conditions to Florida, Georgia, and the Carolinas. Traditionally, these two regions account for a large percentage of the annual acreage burned for the US. As you can see from the the NOAA statewide rank anomaly map below, for July - November, California was one of the few states that was dry during the peak part of fire season. This was a result of the quasi-stationary ridge of high pressure over the East Pacific for the majority of the year.



To a certain degree, luck was a significant component this year, as a major weather event like the 2008 Lighting Bust or the 2007 Santa Ana wind event simply did not occur in 2013. The Rim Fire, which burned into Yosemite National Park and ended up being the third largest wildfire in California history, was caused by a hunter's illegal campfire. The fire eventually consumed over a quarter million acres, and shows what the potential of the 2013 California wildfire season could have been if weather played a greater role.

Have a great Christmas, everyone, and I'll be back on Friday with a new post.

Jeff Masters, with major help from wunderground's fire weather expert, Kari Strenfel