Climate change, as I’ve often heard Brad Udall point out, is water change. By that, Brad means that the effect of a changing climate on people and ecosystems is most clearly felt through changes in how much water there is.
I’ve been thinking about this question a lot as I work on three related projects – one in class with UNM Water Resources Program students, and two collaborations on papers with students and colleagues – that look at the implications of declining river flows on the Lower Colorado River.
In trying to model the impact of climate change on a particular piece of the environment (perhaps the Colorado River Delta or the Salton Sea) or some human community (Las Vegas, for example, or agriculture in the Imperial Valley) we want to model the impact of a reduction in available supply of water. So we model the baseline – how much water we have now – versus some sort of climate change projection of reduced flow. Brad’s “Twentyfirst Century hot drought” paper, with Jonathan Overpeck, offers some numbers. We should expect a 20 to 30 percent reduction in flow by mid century, they found, maybe 35 – 55 percent by the end of the 21st century.
I’m not saying these are the right numbers, but they’re reasonable and citable numbers that we can plug into the models my colleagues are developing to say “What if?”
It’s not wrong to do it that way, but it avoids by simplification one of the central climate change impact questions, because in reality the impact of climate change’s “water change” won’t play out that way. Reduced flow in the Colorado River is funneled through a bunch of upstream dams and diversions, which are managed according to a set of rules.
Those rules in effect act as a funnel through which the impact of climate change flows. If climate change reduces the flow in the Colorado River by 20 percent, does everyone share in those reduction equally? Do some users see a 40 percent reduction, while others see a 10 percent reduction? Do the farmers in Imperial have a senior right, meaning they won’t lose any water? Does the environment take an even bigger hit, or do we decide the environment has suffered enough and impose bigger cuts on farms and cities?
Partly this is in part about contested interpretations of existing rules, and in part about negotiating new rules. This is where the interesting climate change questions lie for me right now – in the water policy funnel.