ALBUQUERQUE, N.M. — June’s rainfall goose egg in Albuquerque means we’ve finished the first half of 2011 with just 0.19 inch of precipitation, by far the driest start to a calendar year on record. It’ll take a while to get data from around the state, but it seems likely that we’ll soon be able to say the same thing about conditions statewide. In addition, four of the first six months were warmer than the long term average, according to National Weather Service data.
Which raises the question: as forests around the state, set up by a weather year by all measures remarkable, go up in flames, are we looking at a “new normal” set of conditions as a result of our greenhouse-driven changing climate?
It’s a surprisingly tough question to answer, entangled as it is in the complex changes to our forest ecosystems that have resulted from a century of human “management”. But the scientists I’ve talked to give a qualified “yes”.
Consider this, from Park Williams and his colleagues in the Proceedings of the National Academy of Sciences last year:
Forests within the southwestern United States appear particularly sensitive to drought and warmth…. Our results suggest that if temperature and aridity rise as they are projected to, southwestern trees will experience substantially reduced growth during this century. As tree growth declines, mortality rates may increase at many sites. Increases in wildfires and bark-beetle outbreaks in the most recent decade are likely related to extreme drought and high temperatures during this period.
Or this, from Tony Westerling and colleagues in Science magazine in 2006:
[W]ildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.
When I caught up with Westerling this week by phone from Merced, Calif. (where’s it been remarkably wet this year), he explained how complicated this is. His seminal 2006 Science paper shows the strongest effect of warming in the Northern Rockies, where the shift from wet and cool to warmer and drier has been more pronounced. Our forests were already warm and dry, Westerling said, so the effect of warming here in the arid southwest is less pronounced. But it is here too, he said.
The University of New Mexico’s Grant Meyer, who has studied fire history across the west, agrees that climate change is a big part of the explanation for what we’re seeing here this year. Here’s what he told Pete Spotts of the Christian Science Monitor:
From the standpoint of geological history, “these big, severe fires are not unprecedented” in hot, dry intervals the region has experienced during the past 10,000 years, says Grant Meyer, a geologist at the University of New Mexico in Albuquerque who studies the interaction of climate and weathering processes – which can be affected by wildfires – on the landscape.
“But recent experience down here suggests that what we’re looking at in the last few decades is at least as severe and maybe more so than anything we’ve seen since the last Ice Age,” he adds.
But Meyer, Westerling and McDowell (and a number of other scientists I’ve been speaking with) all raise a second issue: forest management. Scientists using tree ring fire scar studies have concluded that forests like those around Los Alamos and Santa Clara Pueblo once burned frequently, once a decade or so. They were low-intensity fires that would usually burn along the ground, clearing out the forest and leaving a park-like setting of big open large trees behind. With fire suppression and grazing (which removes the grasses that carry low-intensity ground fires), the forests have become choked with undergrowth. The undergrowth burns hot and carries fire to the crowns of the big trees, creating the conditions that, when combined with drought like we’re having now, bring explosive fire behavior like we saw with Las Conchas this week.
So it’s clear we have a “new normal” here, but that a changing climate is only part of the story.
I’ll have more in Sunday’s Albuquerque Journal.
Note: precip data from the excellent folks at the National Weather Service’s Albuquerque office, who have been a terrific help in my coverage of the drought