Signs Pointing to Green River and Lake Powell, Hanksville, Utah
John Fleck links to an article on the difficulties facing water managers as the consequences of climate change become more and more apparent. It’s bad enough that changes in temperature and hydrology so far have made it clear that there isn’t enough water available in many areas to meet current and projected needs, but a more fundamental problem is that the process for designing water management systems is based on the assumption of stationarity, defined in a recent article in Science as “the idea that natural systems fluctuate within an unchanging envelope of variability.” Thus, while the amount of precipitation or streamflow volume obviously vary from year to year, if stationarity holds it should be possible to take a bunch of measurements over a significant period of time and figure out the amount of variability in the measurements, and thus the range of outcomes to be expected. Systems can then be designed to work in situations within that range.
McPhee Reservoir, Dolores, Colorado
The problem, though, is that climate change is now making stationarity a thing of the past. Things are changing so rapidly, and so drastically, that it’s not at all clear what the range of possible variation is or how much it’s likely to change. What is clear, though, as that same Science article convincingly argues, is that stationarity no longer applies. The range of variation seen in the past no longer has any relationship to the range of variation seen in the present. Thus, the systems designed with stationarity in mind are increasingly unlikely to work, and there is an urgent need to come up with new ways of designing systems taking into account current conditions.
Cochiti Dam
This is, of course, extremely difficult to do in practice, especially since no one knows quite what future changes are going to occur and how the enormously complicated and interconnected natural systems under discussion are going to react to drastic change. But it really does need to be done, since reliable water supplies are essential for communities all over the world, and water managers are responsible for providing that water regardless of what the climate does.
Colorado Division of Water Resources Office, Cortez, Colorado
People often think of global warming in terms of rising mean temperatures, but while that is certainly a big part of it, probably a more important part of the changes seen so far, from a practical perspective, is the increased variance. “Paleohydrologic studies suggest that small changes in mean climate might produce large changes in extremes” is how the Science article puts it, and this is also something that Hal Salzman discussed in his talk yesterday. From a management perspective, it’s those extremes that are most worrisome, and the apparent correlation between a small increase in mean global temperature and a much larger increase in the frequency of extreme events is a big problem (although the article’s authors do caution that “attempts to detect a recent change in global flood frequency have been equivocal”).
Houseboats in Storage, Hanksville, Utah
Mitigation of the effects of climate change has been the focus of the policy conversation on a large scale recently, and the upcoming Copenhagen conference will attempt to bring the global community to an agreement on how to implement effective mitigation procedures. Even if that effort ends up being totally successful (and signs are not looking good right now), however, it’s very unlikely that any change for the better will appear soon. Given how the greenhouse effect works, and the amount of carbon dioxide already in the atmosphere, warming is likely to continue for a while even if very aggressive and successful mitigation techniques go into effect.
Los Angeles Department of Water and Power Office, Lone Pine, California
So while mitigation is the focus of the media and the political elites, to the extent that either gives much attention to this issue at all, on the ground level adaptation is the main concern now. Whatever happens in Copenhagen in December, the Colorado River is running out of water now, and the people in charge of using that water need to know what to expect next and what their options are. Without stationarity it becomes very difficult to say, but that’s no excuse for silence.
Far View Reservoir, Mesa Verde
In his post John mentions that Arizona seems to be facing this issue much more forthrightly than New Mexico. I suspect one of the main reasons for that is the important position of the University of Arizona in the study of paleoclimatology. Tree-ring studies, among the most important methodologies used in piecing together the climatic record going back thousands of years, were literally invented there, and the Laboratory of Tree-Ring Research still plays a major role in both dendrochronology and dendroclimatology as applied to many questions in climate science. Other methodologies are used as well, of course, and Julio Betancourt‘s work on packrat middens is particularly well-known. John mentions Betancourt specifically for his efforts in bringing his ideas to a wider audience, and in that connection it’s interesting to note that he self-archives many of his papers, which are available as pdf files on his website. In addition to being one of the authors of the Science article I mentioned above, Betancourt has also done a lot of work in Chaco Canyon and contributed to many of the recent findings about the correlations between climatic events and cultural activity in the ancient southwest. In some ways he is the crucial link between the study of the ancient southwest and the study of modern climate change, and his research demonstrates one of the important things I’m trying to show on this blog, which is how closely connected those two areas of inquiry really are.
Civil Engineering Plaque at Mesa Verde
As we struggle with the power politics of climate change,* I can’t help wondering how all of this will appear from the perspective of 800 years hence, when scholars who study our culture ask, as we do of the Chacoans 800 years past, “what were they thinking?”
*http://www.nytimes.com/2009/09/25/opinion/25krugman.html?em=&adxnnl=1&adxnnlx=1253982412-9J5uw1eJDadCalCvyEUjFQ
You have accurately described Julio’s scientific contributions. I’m curious, though: Per this statement: “Betancourt has also done a lot of work in Chaco Canyon and contributed to many of the recent findings about the correlations between climatic events and cultural activity in the ancient southwest.”
Are you implying that climate change (e.g., multidecadenal drought) is the main forcing action responsible for Chaco’s collapse and the wider depopulation in the 1300s? All the big SW archaeologists I have spoken with acknowledge it as a trigger but are reluctant to put such emphasis on climate. Might we worth a blog post from you at some point, exploring why this is so.
It’s a complicated issue, and I probably should do a post on it one of these days, though I think I should do some more reading first. The consensus view among archaeologists these days seems to be that drought was definitely a factor, but probably not the only factor. My statement about Betancourt’s role in this was really just to point out that the fact that we can be arguing about this at all is due to the enormous amount of work he and others have put into reconstructing the paleoclimate.
One thing I will note now, though, is that when it comes to Chaco specifically there are really two different events to look at, which may or may not be related either directly or indirectly. (Your comment alludes to the distinction, but I think it’s useful to draw it out a bit.) The first is the “collapse” of the Chaco system, whatever it was, around 1130, which seems to correspond to a period of extended drought. This is when population seems to shift away from the central San Juan Basin and toward the upland areas on the edges of the basin, including Mesa Verde. The twelfth century in general is a really difficult period to understand, but it seems to be very important for understanding the long-term dynamics. By the early 1200s things seem to stabilize a bit, and a new equilibrium of sorts seems to have arisen, with population concentrated in aggregated villages in defensible locations, including but not limited to cliff alcoves.
Then comes the “Great Drought” of 1276 to 1299, and everything falls apart to a much greater degree than it had in the 1100s. Everything north of the San Juan River is abandoned, and people seem to be moving all over the place while at the same time changing their material culture in ways that make them hard to track. The dust clears by 1350 or so, at which point the Pueblos are in more or less the same places the Spanish find them two hundred years later.
Now, both the collapse of Chaco in the twelfth century and the depopulation of the region in the thirteenth seem to coincide quite strikingly with periods of extended drought, which certainly suggests that climatic conditions played a role in these events. On the other hand, estimates of carrying capacity have suggested that regional population never came close to exceeding the carrying capacity of the land, especially in the Mesa Verde area, which is extremely fertile and even today primarily agricultural. So it’s pretty clear that it wasn’t lack of food, per se, that caused the depopulation, but the timing of the droughts suggests some sort of relationship. There are various theories out there to try to explain these events, but it’s a very difficult problem to address.