Arizona’s on fire, with no sign of a monsoon rescue yet massing on the horizon.
Well, get used to it.
Both climate models and recent trends suggest the rise in global temperatures will cause the monsoon storms that deliver almost half of the annual rainfall in Arizona and New Mexico will come later, hit harder and linger longer.
That’s bad news in Arizona’s white-knuckle fire season, which this year has caused a host of fires across the Southwest — with two fires having already made a run on Rim Country communities.
Normally, the monsoon starts in early July. Afternoon thunderstorms laden with moisture sucked in from the Gulf of California and the Gulf of Mexico deliver lightning, strong winds and localized heavy rain. Heated air of the desert rises, creating a vast area of low pressure that draws in wet, cool air from the ocean. Shifts in sea surface temperatures known as El Niño or La Niña affect both winter snowfall and summer storms in Arizona. This year, the sea-surface temperatures have left forecasters uncertain.
So we’ve staggered into mid-July now, with forecasters still not seeing the buildup of a strong, low-pressure system over the desert able to suck moist air in off the ocean. Those storms blast through the desert, delivering 2-4 inches of summer rain to the Valley and 6-8 inches of summer rain in the mountains.
The delay in the monsoon this year has left fire crews coping with extreme heat, bone dry fuels, high winds and dry lightning storms. A glimmer of hope for the return of monsoon storms comes this weekend with the National Weather Service predicting a 20% chance for rain.
Inciweb is tracking 14 significant wildfires in Arizona and four more in New Mexico. The most dangerous at the moment is the 572-acre Polles Fire, which has already claimed the life of a firefighting helicopter pilot. The Polles at one point prompted pre-evacuation notices in Pine and Payson. Earlier, the 193,000-acre Bush Fire prompted the evacuation of Tonto Basin and could have made a run up the hill into Payson if fire crews hadn’t stopped it with backfires and a little help from a shift in the winds.
So is this the frightening new normal?
Quick answer: Most likely, but it’s complicated.
The average monsoon will likely start later and linger longer as global temperatures continue to rise, according to a study published in the Journal of Geophysical Research.
The start of the monsoon will likely shift from July into August, while the end of the monsoon will likely shift from September into October, concluded researchers from the Earth Institute at Columbia University based on computer modeling.
The total amount of rain might not change much, but the shift into August could add a month to Arizona’s already terrifying fire season.
The shift will likely reduce crop yields, increase wildfires, dry out soils, make life even tougher for ranchers and stress water supplies — even if more rain falls in September and October concluded the researchers.
And the shift may have already started, according to a study by the University of Colorado researcher Katrina Grantz published in the Journal Climate. She found a decline in rainfall in July since the late 1940s, with a corresponding increase in August and September rain. Researchers caution that the monsoon remains extremely variable, so sometimes patterns in the short term are hard to detect.
But wait. It gets worse.
Monsoon storms have also gotten more intense in recent decades. The average amount of rainfall during the monsoon hasn’t changed much, but the storms come in more intense bursts. That means the storms may cause more destructive flooding once they hit, according to a study by the U.S. Department of Agriculture posted on the Science Daily website.
That’s exactly what happened to Flagstaff when the 15,000-acre Schultz Fire seared a mountainside above town in 2010. A high-intensity monsoon flood followed, killing a 12-year-old girl in a residential neighborhood as debris-laden water rushed off the burn scar. The fire and flood prompted Flagstaff to adopt a tough wildland-urban interface (WUI) building code, pass a bond to hasten thinning work in the forests around town, establish a fire department brush-clearing crew and enact a strong Firewise brush clearing ordinance. None of the equally vulnerable communities in the White Mountains or Rim Country have taken similar precautions.
However, changes in the monsoon will most likely both increase the wildfire danger in Arizona and also increase the risk of a dangerous flood on seared slopes once the summer rains finally arrive. Gila County Supervisor Tim Humphrey at a public meeting recently implored Congressman Paul Gosar to lobby for money from the federal government to prevent summer rain runoff once the storms start from destroying critical roads in the Tonto Basin, as water careens off the slopes denuded by the Bush Fire.
The U.S. Department of Agriculture study found that monsoon rains have become more intense since the 1970s. The same amount of rain falls in a much shorter time in 6% to 11% of the storms. and the number of rainfall events has increased by 15% during the 1961-2017 period.
“We attribute these monsoon rain increases to climate change in the Southwest, which the General Circulation Models predicted would happen if the atmosphere gets warmer, said University of Arizona researcher Eleonora Demaria, who co-led the study.
The monsoon trends underscore the importance of the U.S. Forest Service’s effort to reduce crown fires and safeguard reservoirs by drastically reducing tree densities on 2 million acres in northern Arizona. Unfortunately, this effort has been largely stalled for nearly a decade by the lack of a market for the small trees and other biomass that make up half of the material loggers would have to remove. The trend also doubles the importance of the kinds of protective measures Flagstaff has taken.