Global Warming Will Impact Rim

Federal study projects a 4-10 degree temperature increase in the Southwest


Best we finish the Blue Ridge pipeline, thin those spindly forests, keep all our fire insurance policies up to date. Oh, yeah, and don’t get too fond of pinon pines.

That’s because some of the nation’s scientists say Rim Country could get very thirsty in the next 50 years — and that already struggling forests could burn like a scene from a bad disaster movie.

Those now seem like some of the most likely results of accelerating global climate change on the Southwest, according to a report released this week by the United States Global Change Research Program.

The region has already experienced some of the sharpest average temperature increases in the country — up an average of 1.5 degrees compared to a 1960-1979 baseline period, concluded the report released by the White House.

By the end of this century given current trends, temperatures in the region will rise 4-10 degrees above that baseline, much of that increase likely due to the heat-trapping effects of “greenhouse gas” pollutants like carbon dioxide, the report said.

That temperature increase could have dramatic and sometimes contradictory effects.

For instance, winter snowpacks will likely decline — but warm-weather flooding could increase.

The drop in snowfall could put southerly elevation ski resorts like Snow Bowl and Sunrise out of business — and wreak havoc with winter recreation in Rim Country based on things like snowmobiles and cross country skiing.

The decline in snowpacks could also have a big impact on the Colorado River and other major rivers. The Colorado supplies water for millions of people in seven states, but those states based their division of water on an especially wet period. As a result, the river already falls several million acre-feet short in an average year of the present allocation.

The projections suggest average rainfall over the Southwest could decline somewhere between 15 percent and 40 percent — depending on the assumptions about future emissions of heat-trapping gases.

The report said even the modest average warming in the past 50 years helped produce the worst drought in 110 years of recordkeeping.

The report also said this most recent drought is dwarfed by other, decades-long dry spells in the region, when greenhouse gasses weren’t an issue. Tree ring records going back 2,000 years have shown the effects of several such megadroughts.

The projected decrease in average rainfall in the face of continued population growth will likely cause the region’s long, bitter water wars to heat up. Fortunately, the Rim Country by about 2013 will likely have 3,500 acre-feet per year delivered through the Blue Ridge pipeline, drawn from a 14,000 acre-foot reservoir atop the Rim. Payson right now uses about 1,800 acre-feet of water annually and rainfall deposits about 2,400 acre-feet annually into the underground water table in an average year.

That supply could help insulate Rim Country for a struggle for water from much more powerful regions in a drier future.

Still, the Rim Country could suffer many other side effects from a temperature increase.

The already stressed and fire-prone forest may become much more vulnerable to blowout fires, the report said. That could mean fewer quiet fire years like the one just concluded — buffered by a good snowpack and a wet May — and more bone-dry years like the one that spawned the 500,000-acre Rodeo-Chediski Fire.

An increase in fires and severe, warm-weather storms could ultimately threaten the area’s hard-won new water supply. The Blue Ridge Reservoir atop the Rim is surrounded by thick, overgrown forests. A fire in that region could increase erosion, which could eventually fill in the reservoir.

The U.S. Forest Service is already clearing buffer zones around Rim communities and has shifted to letting naturally caused fires burn when possible.

A century of grazing and fire suppression has left millions of acres of forest crowded with 10 to 20 times as many trees as they had before the arrival of Europeans. Less precipitation would stress the ponderosa pines, making them much more vulnerable to wildfires and insect infestations.

Rim Country residents would also likely also see dramatic changes in vegetation, since the region compresses major changes in habitat types in a small area.

As the temperature warms, plants will change the altitudes at which they grow. Some plants seem especially vulnerable to temperature change — like the pinon pines that mingle with juniper to the south of Payson. Payson sits right at the overlap between the ponderosa pines that dominate atop the Rim and the pinon/juniper that dominates at lower elevations.

On the other hand, many of the specific, regional changes remain hard to predict. For instance, none of the climate models seem to provide consistent predictions as to what will happen to the region’s distinctive pattern of “monsoon” summer storms.

The temperature increase could shift storm patterns north or east.

On the other hand, the warming waters of the Gulf of California and Gulf of Mexico could produce more, wet monsoon storms — offsetting some of the decline in rainfall, the report concluded.


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

Requires free registration

Posting comments requires a free account and verification.