El Nino influences on Oklahoma’s upcoming wildfire season

Wednesday, November 25, 2015

Wildfire is always a hot topic this time of year. The dormant season, which occurs from November through early April in Oklahoma, usually sees the majority of fires on an annual basis.

This season has two opposing factors moving the fire danger zone needle. The first is the large amount of rainfall that fell on a major portion of the state this spring and summer.

“Rain fostered the growth of vegetation and as a result, many areas of the state have greater than normal herbaceous and small woody shrub fuel loads,” said J.D. Carlson, fire meteorologist at Oklahoma State University and program manager of OK-FIRE. “This factor would tend to increase the likelihood of wildfires, as well as more intense ones.”

Carlson also is part of a research team at OSU that has investigated the linkages of soil moisture to wildfire activity.

“One part of the study showed there is a positive correlation with large wildfire frequency in the dormant season if soil moisture is high during the previous spring, like it was this year,” he said. “This makes physical sense as higher soil moisture results in greater growth of wildland fuels, which can subsequently burn during the next dormant season.”

The good news is the second factor, which can lead to a decrease in wildfire activity. The El Nino regime, which we are currently in, is expected to peak during the dormant season. El Nino is the warming of the eastern Pacific waters and this El Nino is expected to be one of the strongest in history, which generally results in above normal precipitation across the southern United States.

“The latest long-range outlooks for the country just came out and show above normal precipitation is expected for all sections of Oklahoma through the end of the dormant season,” Carlson said. “Temperatures have equal chances of being below, near or above normal.”

This outlook, coupled with the strong El Nino, is likely to reduce chances for extended periods of large wildfire activity during November through April. Frequent storm systems, driven by a strong jet stream coming from the Pacific, would traverse our region, giving regular periodic precipitation and raising relative humidity levels.

During the dormant season, the main wildland fuels available for burning are dead grasses and deciduous woody plants that have gone dormant.

“Evergreens, like pines and eastern redcedar, can burn but with the good soil moisture we had in many parts of the state this past spring and into early summer, they should be in pretty good shape,” Carlson said. “If I had to make an educated guess, I would argue for reduced wildfire activity this upcoming dormant season, especially with respect to larger multi-day events.”

However, it is important to remember that with the greater-than-normal grassy fuel loads in many parts of the state, it does not take much time for these to dry out and be suitable for combustion. With periods of low relative humidity and moderate to strong winds, wildfires can occur, even after a recent period of heavy rain.

“Best to be on guard and monitor the day-to-day fire weather conditions,” said Carlson. “OK-FIRE (http://okfire.mesonet.org) is a great tool for this, providing current and forecast fire weather and fire danger information up to three days in the future.”