Monsoons Huff And Puff But Yield Little Rain

Advertisement

Rim Country’s almost-monsoon season this week brought dangerous flashes of lightning, but not much of the rain needed to dampen fire danger and reopen the forests on which the region’s tourist-oriented economy depends.

Fortunately, with El Niño conditions shaping up in the Pacific, forecasters hope for a near-normal monsoon season and a better-than-average winter, which may mitigate the fierce drought that has drained reservoirs and spiked fire danger.

But don’t get all optimistic: An increasing number of climate models predict we’re in for more extreme weather and lightning strikes in the years ahead.

Lightning this week sparked half a dozen small fires in the Tonto National Forest, mostly on the outskirts of the Valley. Lightning starts almost half of all brush fires in the Southwest. Elsewhere, people start the great majority of fires.

Monsoon storms gathered around Payson this week, staging spectacular displays of lightning for brave weather junkies seated in the Airport Road monsoon grandstand seats, but failed to deliver the drenching rains the region so desperately needs. So far this year, Payson has gotten about 2.6 inches of rain, compared to the normal tally by this point of 9 or 10 inches.

Rim Country has more lightning strikes than almost any other area of the country, due to the long, high barrier of the Mogollon Rim, which spawns repeated thunderstorms during the monsoon season. Arizona suffers 600,000 lightning strikes annually, which kill roughly one Arizona resident each year, according to University of Arizona climate science specialist Mike Crimmins.

The National Weather Service predicts a 50 percent chance of rain in Rim Country today and tomorrow, dropping to 40 percent on Sunday. Normally, the region gets half of its total annual rainfall during the monsoon season — which extends from mid June through September.

Lightning stems from static discharge between water vapor and ice particles in a thunderhead. As the particles collide, they pick up or shed electrons, building up large electrical fields in the clouds. Once the field gets strong enough, a spark jumps between different regions of the cloud, between the cloud and the air or between the cloud and the ground. A lightning bolt can generate a billion volts of energy and reach temperatures of 50,000 degrees.

Each year, Arizona lightning strikes spark an average of 2,300 fires, which consume 277,000 acres. In the past week, lightning strikes are the suspected cause of a 161-acre brush fire near Superior, a 250-acre fire northeast of Bartlett Lake, and three small fires near Black Canyon City totaling 4,000 acres. Most of the active brush fires in Arizona now are in the Coronado National Forest east of Tucson, where the monsoons have been the most active. That includes the 7,500-acre Fox Fire, the 8,000-acre Grapevine Fire and the 1,700-acre Cottonwood Fire.

The Forest Service has posted firefighting aircraft at the Payson Airport, which spent the week rushing to douse fires before they could get out of control.

The frightening fire seasons of the past two years may become the new normal, if the climate predictions come true.

The National Oceanic and Atmospheric Administration last week reported that last winter was the fourth-warmest on record in the United States; this spring was the warmest since record-keeping began in 1895; and April ended the warmest 12-month period in U.S. history.

photo

NOAA photo

A steady rise in global temperature matches a steady rise in atmospheric concentrations of carbon dioxide and other greenhouse gases, most of them linked to pollutants produced by humans. Climate scientists like Jack Williams, director of the Nelson Institute for Climatic Research, note that the amount of warming in the past 40 years exceeds anything since we started keeping temperature records.

University of Arizona climate experts note that since 1900, average global temperatures have increased 1.5 degrees F. The pace of the warming has picked up sharply in the past decade, with a .35 degree increase. That has produced progressively earlier snowmelt in Rim Country in the spring, earlier peak stream flows and a decrease in average rainfall.

A wide array of computer models now project a steady rise in global temperatures in coming decades. Some studies have projected longer, deeper droughts in the Southwest. Others have raised the frightening possibility that above a certain average temperature, summer storm tracks will shift north and cut off Arizona’s monsoon season.

A just published study in the Journal of Geophysical Research and Atmospheric Research concluded that lightning activity will increase by 10 percent for each degree of warming.

That could lead to ever-more violent fire seasons, especially when combined with predictions of longer, more severe droughts.

However, at least in the short term, the development of El Niño conditions in the Pacific have substantially increased Rim Country’s odds of a nice, wet winter.

Trade winds blowing from the eastern Pacific have already started to slacken, which allows warm surface water to move east. As a result, the storm-steering Pacific jet steam straightens out and shifts to the south. Come winter, that increases the odds Pacific storms will dump snow on Arizona.

Between 1896 and 2002, half of the El Niño winters produced at least 115 percent of the normal rain and snowfall. Only 25 percent of those winters produced below-normal rainfall.

Even normal winter rain and snow would provide a vital infusion of moisture. The U.S. Drought Monitor shows Gila County in “severe” drought — along with most of Arizona. A swath of Arizona between Gila County and the Colorado River remains in “extreme” drought.

Two years ago, Roosevelt was brimming, but now it has shrunk to 55 percent of its capacity. Tonto Creek and the East Verde River have all but dried up and the Verde River has about one third of its normal flow. The Salt River has less than half its normal flow. That low flow in the Salt River last week spurred an algae bloom that killed thousands of fish.

Comments

Use the comment form below to begin a discussion about this content.

Requires free registration

Posting comments requires a free account and verification.