This year’s sharp decline of elegant trogons in the face of record drought “is just another piece of the overall jigsaw puzzle that is alarming or should be alarming, regarding climate change,” as Southern Arizona naturalist and trogon researcher Rick Taylor sees it.
“You shouldn’t see such radical population swings; you should not see this in trogons, all things being equal,” Taylor said of this year’s Tucson Audubon Society survey that found 68 of the flaming crimson-colored birds in five Southeast Arizona mountain ranges compared to 201 in 2020.
But the scientists who study climate and our changing climate do not all agree on whether or how much of a footprint our continuously warming weather has had in this latest drought.
As some climate scientists see it, the link between this region’s recent rainfall deficit and human-caused climate change is not clear-cut. Two say there’s no way to know if this region’s recent extreme dry weather is tied to climate change without doing a full-scale study of the kind that have increasingly been conducted in recent years of short-term climate phenomena.
But a third climate scientist said he tends to err toward the view that “there’s something wrong here,” causing not just this event but several other drought-related problems.
“Without an actual formal analysis, it’s really impossible to put specific numbers on any climate change contribution,” said Benjamin Cook, an adjunct associate research scientist at Columbia University’s Lamont-Doherty Earth Observatory. “To try to determine the link between climate change, drought and the trogon declines, I think would really require a highly specific localized analysis that would include at least some information on the habitat these birds are living in or traveling through.”
A prominent University of Arizona climate scientist, Michael Crimmins, said he thinks that the 18 months of record low rainfall that has plagued this region since late 2019 most likely has natural causes. He agrees, however, that the dry weather and its impacts on wildlife could have been aggravated by the extreme heat that struck this region last summer and early this summer.
“It doesn’t mean climate change hasn’t in some way maybe moved the needle on that,” said Crimmins, an assistant professor and climate science extension specialist for UA’s Department of Soil, Water and Environmental Science. “You can’t say that climate change didn’t cause the drought last summer. It doesn’t seem like the main cause.”
A UCLA climate researcher, Daniel Swain, said that climate-related computer models don’t necessarily suggest that any decreases in precipitation should have occurred due to climate change.
“That leads most scientists to conclude that the recent decrease in precipitation in the Southwest, by itself, can’t definitively be linked to human-caused climate change,” said Swain.
But Swain is co-author of one recent study that does suggest Arizona and California could be in for more extreme dry and wet periods in the coming years as temperatures warm up.
UA’s Christopher Castro said he sees the climate change impacts not just on this event, but on a wide range of individual, extreme weather-related events such as the latest dry spell becoming more apparent as time passes.
“I tend to err on the side that there’s something wrong here. There’s a variety of metrics we can look at,” said Castro, a professor and associate department head for UA’s Hydrology Department. “Whether it’s things like temperature extremes, the soil moisture declines, changes in species and ecosystems, changes in wildfire intensity and coverage, these things start to reach a point to the public mind it becomes pretty obvious” that climate change is a factor.
With both natural and human systems reaching critical threshold points for approaching failure, whether its threatened Colorado River supplies or the destruction of 60 percent of the Catalina Mountains’ forests in one fire, “we’re observing changes that are unprecedented,” Castro said.
Record-breaking drought
There is no doubt Southern Arizona’s drought is breaking records. From June 2020 through May 2021, the region received 5.98 inches of rain, the lowest on record, National Oceanic and Atmospheric Administration records show. It was more than 8 inches below the normal rainfall for that period.
The record dry spell followed a broader, April 2020 study that warned the entire Southwestern U.S. was in an emerging megadrought, stretching from 2000 to 2018. It said 47% of the drought’s severity was attributable to human-caused climate change impacts, as estimated from 31 computerized climate models.
The study used tree ring reconstructions of summertime soil moisture data and computer modeling to conclude 2000 to 2018 saw the second driest megadrought since 800 A.D.
But the study was focused specifically on droughts in soil moisture, not precipitation, said Columbia researcher Cook, one of nine co-authors. In fact, the study found a slight increase in precipitation over the entire region during that period but concluded it was overwhelmed by other forces to produce the megadrought.
While the study’s researchers found a clear human signal in the soil moisture drought, “our results were consistent with other studies that have found no climate change signal specifically in precipitation,” he said.
A second study, published in April 2021, found a dramatically different trend: The Southwest’s annual precipitation had dropped 3.2 inches from 1976 through 2019, mostly since 2000, and the entire West’s precipitation had dropped four-tenths of an inch in that period. Its co-authors included Prof. William Smith of UA’s School of Natural Resources and the Environment.
Responding to the megadrought study, trogon researcher Taylor commented that even if our long-term drought is in soil moisture, not rainfall, “common sense tells me if there’s less moisture in the soil, it’s going to echo through everything.
“Plants aren’t going to be productive. They’re not going to put out as much foliage. Herbaceous growth — plants lacking woody stems — is especially going to be limited. Insects that feed on that sort of thing, they’re going to be reduced in number because of a limited food supply,” said Taylor, a self-described “non-credentialed scientist” who has monitored trogons in Southern Arizona’s Sky Islands since 1976.
“If you say soil moisture content is low, and that’s probably more important than low rainfall as far as the drought is concerned — the consequences are about the same,” said Taylor, whose field guides to Southern Arizona birds have been reprinted numerous times over the years.
UA’s Crimmins noted that the second study showing Southwest precipitation declines covered a only short period of those declines, since the 1970s and 80s were wet and a drought came afterward.
“You drag that backward, and the 1950s had a drought period in it. I don’t get that excited about precipitation trends down here. As you drag out that sample of time that’s studied, you just see cycles of precipitation” rising and falling, he said.
But a 2018 study that was based in California suggests that it and Arizona could be in for more, future alternating extreme wet and dry spells as the climate continues heating up, UCLA researcher Swain said.
Despite the lack of any detectable long-term trend in mean annual precipitation, climate models strongly suggest an increase in future wet and dry extremes in similar proportions, he said, using the term “precipitation whiplash” to describe such weather cycles.
The study’s authors did not formally extend that research into Arizona, but most of this state is shown in figures illustrating the study, he said.
“The increase in climate model-projected ‘precipitation whiplash’ does indeed extend into Arizona, suggesting that a similar process could play out there,” he said.
