Home on the range — where seldom is heard, a discouraging word.
Well, not exactly: Leastwise, not when it comes to research on how shifts in the climate will likely affect the forests of Rim Country — and the rest of the West.
So here are some of the recent gleanings for assorted published studies.
Wildfires will worsen
By 2050, a steady rise in average temperatures will likely increase the high-risk wildfire season by about three weeks, according to a group of Harvard researchers who published their estimates in the journal Atmospheric Environment.
The researchers concluded that the projected increases in average temperatures — especially in the winter — would result in a two- to three-fold increase in megafires, like the disastrous Rodeo-Chediski Fire or the massive Wallow Fire. That’s partly because the peak fire season would likely start in April rather than May or June — and could extend into August, especially if climate shifts delay or diminish the monsoon storms that now bring the fire season to a close.
This perhaps 300 percent increase in big fires will also produce a roughly 20 to 50 percent increase in smoke throughout the region, bad news for people in the region with respiratory ailments or folks who like to stand atop the Mogollon Rim and gaze off into the 100-mile distance.
Not as bad as the Ice Age
Granted, the average temperature has risen by about half a degree per decade for the past 40 years in and around Flagstaff, according to a study by Kenneth Cole at Northern Arizona University. Moreover, that warming trend appears likely to continue for years to come, perhaps forcing major changes in the forests throughout Northern Arizona. Then again: It ain’t nothing compared to the end of the last Ice Age about 12,000 years ago. Tree ring data suggests that average temperatures rose by about 7 degrees in the incredible space of just 50 years — making it two or three times as rapid as the current warming trend. Of course, that shift wiped out mammoths, camels, giant ground sloths and a host of other species that once wandered the wilds of Arizona.
Say goodbye to the aspen
The warming trend will likely mean bad news for the state’s already struggling aspen groves, those tremulous stars of autumn and one of the most wildlife friendly trees in the forest, according to a study by Margaret Moore, Peter Fule, Thomas Zegler and Robert Keane with the NAU school of forestry. The team set out to investigate the still mysterious decline of aspen groves throughout the Southwest. They found that growth rates vary among different aspen. Generally, the fast-growing trees have survived better than their slower-growing siblings — apparently because they can recover better after heat spells and dry periods. They also found that higher maximum temperatures in June resulted in significantly lower growth rates — offset by a little bit by rainfall. However, the combination of higher temperatures and less rain had a big impact on aspen mortality rates.
Unfortunately, projections suggest that by the end of the century average June temperatures will exceed the aspen’s threshold, resulting in even higher mortality rates throughout the region.
Worst of both worlds
The warming trend in the Southwest will not only produce more droughts — it will likely also deliver more floods, according to an unsettling summary prepared by 120 scientists, including Gregg Garfin with the U of A School of Natural Resources and the environment and presented at a recent conference in Flagstaff. The period since 1950 already ranks as the warmest stretch in the past 600 years. In that period, the timing of stream flows and snowmelt have changed significantly. That change will escalate as a result of a projected 1- to 3-degree (centigrade) rise in average temperatures between 2041 and 2070 and an additional 3- to 5-degree (centigrade) increase between 2070 and 2099. What used to count as a 100-year heatwave will become 10 times more frequent.
Rainfall should decrease by about 5 to 15 percent. Monsoon rainfall on the Colorado Plateau will likely decrease by 20 percent. Meanwhile, the storms that do hit and cause flooding will actually increase.
Worst drought in 400 years
The amount of moisture in the air during the warm months of the year and rain and snowfall in the winter accounts for 82 percent of droughts, according to a tree-ring study by Park Williams, with Los Alamos National Laboratory in New Mexico and presented at a recent conference in Flagstaff. The researchers studied a massive set of tree ring records that showed rainfall patterns for the past 1,000 years. They essentially calibrated the tree ring records with actual rainfall measurements for the 20th century, and then projected backward based on tree ring records dating back to A.D. 1000. The study showed that temperature largely controls “atmospheric moisture demand” in the summer months and therefore plays a crucial role in the development of drought. This summer heat stress translates directly into tree death and decreased tree growth — which also produces more wildfires.
The study also showed that the drought that started in 2000 qualifies as the most severe drought in the past 400 years — although it still falls short of the “megadrought” that continued off and on between A.D. 1000 and 1600. However, unlike past megadroughts, the current dry spell has taken place against the backdrop of a steady rise in average global temperatures. If current climate projections prove accurate, concluded Williams, the 21st century could see shifts in forests globally “unfamiliar to modern civilization.”