It was cool and moist in Southern Arizona’s grasslands last week, but fire managers know that might just be the lull before the firestorm.
State and federal fire managers predict a “normal” fire year in Arizona, except for the grasslands where the fire danger increases to high during the hot, dry month preceding the onset of the monsoon in July.
When grass dries, it burns easily. Fire spreads quickly.
Oracle Fire Chief Larry Southard said he recently witnessed the volatility of the fire fuel category known as “fine fuels.”
When lightning struck a big, dead oak tree during a thunderstorm last week in Oracle, it burned a 14-foot circle of grasses around it, even though it was pouring rain at the time, he said.
The region has a prolific crop of grasses, he said. If they’ll burn in the rain, what happens when they dry up?
For the past decade, Southard has worried mostly about the thickets of drought-stressed oak trees that arc the southern borders of his town.
Six inches of rain this winter, including an unusual (for May) 1-inch soaking last week, brought the drought-stressed oak trees on Oracle’s hillsides out of dormancy but also produced that bumper crop of grasses.
“We have two vegetation types. If it’s not one you worry about, it’s the other,” he said.
Forecasters at the National Interagency Fire Center say Arizona’s grasslands will develop above-normal fire potential between now and the arrival of monsoon moisture in July. That area stretches southeast from Kingman to the New Mexico border in Cochise County and includes Pima, Santa Cruz and Cochise counties.
Some strategic rain over the next two months would be helpful and could be possible, said Chuck Maxwell, meteorologist with Prediction Services at the center’s regional office in Albuquerque. The current weather pattern could bring more rain, and it is not expected to produce sustained high winds, he said.
Our current weather is courtesy of a big pool of warm water in the Pacific Ocean that has migrated eastward — the trigger of the weather pattern known as El Niño, which produces winter rain in the Southwest, said Mike Crimmins, of the University of Arizona’s CLIMAS, the Climate Assessment for the Southwest.
Historical records and weather models are mixed on whether that also means spring rain or a good monsoon, he said.
And things always dry out in June, he said. The high-pressure system that reliably makes June our hottest month is a necessary precursor to the monsoon rains. “When it does dry out, which it will, we’ll see fires,” he said.
The big trees retain moisture from a decent winter rainfall, but snowpack is nonexistent in Arizona. June heat will dry them out, and one fire last month demonstrated that winter grass growth is a problem at higher altitudes as well. That fire was on the western ridge above Summerhaven on Mount Lemon, where the conifer forest was reduced to ash in the Aspen Fire in 2003. It now supports grasses and shrubs.
There is no guarantee the forests won’t burn. A “normal” year does not mean there won’t be fires in the big trees.
Maxwell, of the Interagency Fire Center, said the biggest concern for June is “the whole brush belt area from Kingman down to Cochise County in the 3,000- to 6,000-foot range.” A four- to six-week dry period could move that concern into the heavier timber, he said.
“If and when it happens, it will be a 10- to 14-day transition to ‘game on.’”
For now, things are calm in the grasslands south of Tucson, said Fire Chief Joseph De Wolf of the Sonoita-Elgin Fire Department.
His district covers 350 square miles of grassland in Pima and Santa Cruz counties. His department has had to corral two 20-acre grass fires so far this year, but cool weather has kept the well-watered grasses from growing too tall.
He’s hoping for more rain. “They say we’ve got a couple storms predicted in May,” he said, “but as in every year, we’ll probably be running for three to four weeks in June before that monsoon comes in.”