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Even if our agricultural industry is able to adapt, Tennessee is likely to face problems related to water — an element that can wreak havoc both in scarcity and overabundance. A statement released earlier this month by the Tennessee Commissioner of Environment and Conservation's Water Resources Technical Advisory Committee hints at just how problematic extended droughts could be for our area.
"[S]ome areas of the state are growing fast enough that utilities there are competing for water even in times of plenty," the committee said. "We know now ... that utilities along the main stem of the Cumberland River in fast-growing Middle Tennessee are using more water than the main stem alone can supply."
Since there is already pressure on our water supply, increased demand created by hotter temperatures will only further stress the system. Are we headed toward water rights allocations, as in New Mexico? Will we all be driving dirty cars and taking Navy showers, as we did in the weeks after the 2010 flood? Whatever happens, Tennessee's water infrastructure might be as vulnerable to climate change as it is vital to our adaptation.
"In '07, when we had the big drought," TSU's Browning says, "they were telling livestock producers they couldn't use the water for their livestock, and they had to find other sources, and it became a real issue. So certainly there's going to have to be some planning if that becomes an annual issue. ... Certainly there will have to be some policies."
At the very least, state officials are thinking about how those policies might take shape. Though it didn't mention climate change specifically, the Water Resources Advisory Committee released a statement of goals and principles Aug. 2 that showed awareness of the issue: "Drought conditions, increased demand, economic growth, and competition for water use in the 21st century emphasize the critical need for a continued water use management program in Tennessee." Similarly, a state water supply pilot study coordinated by the Tennessee Department of Environment and Conservation aims to "account for climate change, droughts more severe than those in the record, and inaccuracies in streamflow and precipitation estimates."
Another, less obvious reason water could be at the center of Tennessee's climate change problems: its role in producing the power we'll need to stay cool — and in some cases, alive. As Vanderbilt's Gilligan puts it: "We need water to make electricity — we have a lot of hydroelectric, but even nuclear and coal-burning plants need cooling water. ... We've run into problems in the past when, in the summer, the water temperature in the streams, combined with the decreased levels due to the higher temperatures, [has meant] they have to hold back on the power."
And that's just the scarcity side of the water equation. Between droughts, we could be inundated with more water than we can handle, seesawing between Mad Max and Waterworld. While precipitation is much harder to predict, and models disagree about just how it will play out in the future, a warmer climate means more water evaporating into the air. And while scientists may not able to predict precisely when and where that water will fall, greater heat in the atmosphere creates a greater likelihood for heavy rain. (See chart above.)
"Make no mistake," Heidi Cullen writes in The Weather of the Future, "global warming increases the likelihood of floods."
Randall Gentry, director of the University of Tennessee's Institute for a Secure and Sustainable Environment, says changing storm patterns can have significant regional impacts. "Let's say that during a given month, a region, on average, typically gets 10 inches of rain over 30 days cumulatively," Gentry says. "Under climate change, the patterns of delivery can be altered such that the 10 inches is received in more intense storms." These storms could overwhelm a system calibrated to less extreme downpours.
"Engineers design infrastructure on the basis of frequency of events or risk," Gentry says. "So a one-in-50-year probability storm could occur on a much more frequent basis ... and do great damage."
Given that 50-year heat waves have the potential to become every-other-year heat waves, it is within the realm of possibility that our 1,000-year flood could be more like a 20-year flood by the time this year's kindergarteners finish college. Taken as an isolated event, the great Nashville flood of 2010 could have happened even if the climate is not changing. But a warming climate will increase the likelihood of extreme weather — and make it even more devastating. As Vanderbilt's Gilligan says, citing a NOAA report, the recent drought in Russia happened as part of a natural event called a "blocking high." However, he says, "if the same weather conditions took place in combination with the kind of climate change we are confident will occur over the coming century, the results would be much more severe than what we see this year." In other words, Russia's next heat wave might not only come sooner, it could be even worse — and so might our next flood.
"It's clear that long-familiar patterns are being disrupted, and the extreme events are becoming both more extreme and more frequent," Gore says. "Moreover, the changes — like larger downpours — are absolutely consistent with what the scientists have long warned us would accompany global warming."
As Eric Pooley, author of the new book The Climate War, puts it: "In a warmer world, that kind of thing will happen more often. So if you liked the Nashville flood, you're going to love living in a warmer world."
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