Monsoon storm

A monsoon storm builds over Payson earlier this year, one of few seen this summer.

Arizona may wind up this year with the driest monsoon on record, as wildfires continue to flare and smolder across the state.

Most of the state typically gets half of its annual rainfall during the three-month monsoon, which officially runs from June 15 to Sept. 30. But this year most of the state had gotten less than half a normal monsoon’s worth of rainfall.

After the first wet winter in years, the monsoon fizzle hasn’t yielded disaster. However, climate researchers from the University of Arizona and elsewhere warn that the monsoon will become increasingly erratic in coming years — rampaging and sputtering depending on the fitful gyrations of the jet stream as the planet warms.

This year, Flagstaff has received 2 inches when it normally gets more than 4 inches. Phoenix has gotten about a third of an inch while it normally gets 1.6 inches, Tucson has received 2.2 inches compared to the normal 3.6 inches. according to the National Weather Service.

As of Aug. 13, the monsoon has delivered less rain than any year since the start of recordkeeping in 1899.

Moreover, the forecast for the next week or two predicts more record temperatures than rainfall.

As a result, wildfires have sputtered and flared, including a fast-moving brushfire this week that shut down Interstate 17 near Sunset Point, between Phoenix and Flagstaff. InciWeb lists at least 14 active wildfires in Arizona. Fortunately, only a few of them like the Museum Fire near Flagstaff and the Woodbury Fire in the Superstitions forced evacuations and briefly threatened structures. The first damp dash of the monsoon helped firefighters get these fires under control.

Other fires near the Grand Canyon and in the White Mountains have been muffled by the lingering effects of a wet winter. Crews established perimeters and let the low-intensity fires contribute to desperately needed forest thinning and restoration efforts.

But in the past several weeks, the monsoon has dried up, replaced by record temperatures across the state. Phoenix hit 114 degrees twice last week, setting all-time records for the dates.

The monsoon connects Arizona to planetary climate cycles. The shifts in the high-altitude river of air dubbed the jet stream normally bring storms loaded with tropical moisture boiling out of the Gulf of California and the Gulf of Mexico and across Arizona and New Mexico. Those storms deliver half of the annual rainfall in the desert regions and 30 or 40 percent of the rainfall to the White Mountains and Rim Country.

Normally, Payson gets about 22 inches of rain annually — about 2 inches in August, 2 inches in July, 4 inches in December and another 4 inches in January. Show Low in the White Mountains normally gets about 18 inches annually, with two inches in August and an inch each month from September through February.

Normally, when the surface water in the eastern Pacific warms up — an El Niño — Arizona has a wet year. Mostly, that means more snow in the White Mountains, but sometimes a more active monsoon as well. This year, El Niño conditions produced the first “normal” winter snowpack in years, but then sea surface temperatures cooled, perhaps contributing to the disappointing monsoon. The ebbing of El Niño conditions could produce a dry winter to follow our non-existent monsoon.

Normally, the seasonal warming over the tropics drives increased evaporation from the ocean and the buildup of a high-pressure ridge over Mexico in June. Arizona’s fire season peaks at this point, with an almost rainless May and June combined with the highest temperatures of the year.

This high pressure ridge in July shifts to the southern Plains and southern Rocky Mountains. This opens the door to inrushing tropical storms, producing monsoon storms not only in the American Southwest but in India as well. Normally, this produces fitful storms, including localized deluges and wet weeks followed by dry weeks.

The monsoon varies dramatically from one year to the next. For instance, in 2013 Flagstaff received 17 inches of rain during the monsoon months and Prescott received 6 inches. But in 2014, Flagstaff got 12 inches and Prescott 18, according to the National Weather Service on the Arizona monsoon patterns.

Despite those variations, the monsoon remains critical to fill reservoirs and sustain agriculture across much of the state. The monsoon also plays a key role in the length and intensity of the fire season. Finally, the summer rains largely account for the dramatic differences in vegetation between the saguaro-graced Sonoran Desert and the creosote-dominated deserts of the Mojave in California.

But when it comes to the monsoon pattern in Arizona, abnormal may prove to be the new normal, according to an array of climate studies and projections.

The average temperatures in Arizona have warmed by 2 degrees in the past 50 years, about double the global average, according to a climate assessment issued by the federal Environmental Protection Agency. The warming trend could reflect natural variations, but is likely influenced by the 40 percent increase in heat-trapping carbon dioxide in the atmosphere because of human activities since the 1700s. The surface waters of the ocean have warmed by about 1 degree in the past 80 years, affecting weather all over the globe.

The acreage burned by wildfires in the Southwest each year has roughly tripled in the past 50 years, which reflects both the effect of the average warming and the overgrown condition of the forest. The average snowpack in the state has also decreased by an average of 40 percent, according to the climate assessment — although snowfall still varies tremendously from one year to the next.

The shift has proved especially painful for the vast stretch of northern Arizona centered on the Navajo Reservation, which has remained locked in drought even in years when the rest of the state gets relief. Some 40 percent of the people on the Navajo Reservation live in areas threatened by “extreme heat” issues and 30 percent of the population have neither public sewer or public water systems.

However, intensely localized systems like the monsoon remain notoriously difficult to predict. Some researchers running projected temperature increases through multiple climate models predict the Arizona monsoon could melt away in coming decades. Other projections suggest the pattern may become more violent and unreliable — with monsoon fizzles alternating with epic rainfall and destructive flooding.

So the forecast for 2019 calls for a historically dry monsoon, with more hot and dry to come in the next several weeks.

And long range?

Buckle your seat belt.

Arizona wildfires still burning:Sheridan Fire: 8,600 acres near Prescott

Pemberton Fire: 1,200 acres near Prescott

Saber Fire: 2,000 acres near Flagstaff

Black Mesa Fire: 349 acres at Sunset Point near I-17

Museum Fire: 2,000 acres near Flagstaff

Boulin Fire: 4,300 acres near Flagstaff

Ikes Fire: 5,700 acres near the Grand Canyon

Castle Fire: 20,000 acres near the Grand Canyon

Trumbell Fire: 2,500 acres north of Grand Canyon

Hurricane Cliffs Fire: 282 acres north of Grand Canyon

Contact the writer at paleshire@payson.com

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