Common Tragedies

Thoughts on Environmental Economics

Spillover

Posted by Rich Sweeney on October 23, 2007

In the world of hydroelectric power, “spillover” is a term used to describe water that flows over or around a dam, as opposed to through the turbines. More commonly, of course, “spillover” is a term used by many to describe a side effect or unanticipated consequence. This weekend the New York Times published a very long but very good piece on how global warming could significantly impact the United States’ fresh water supplies. While the article was focussed primarily on the consumptive water demands of the nation, it’s also clear that one of the spillover effects of a warmer world could be an end to the phenomenon of spillover at dams across the country.
Stabilizing carbon emissions is going to be hard enough assuming we maintain our current hydro capacity. Any decrease in hydro-power will only make the task more arduous and costly. Globally, hydro accounts for 19% of total electricity and 63% of elecricity from renewables. In the US, 42% of US renewable electricity came from hydropower in 2006. Complicating matters even further is the fact that hydropower in the US is extremely concentrated. States in the northwest rely heavily on hydro. As snow caps diminish, power customers upstream and farmers downstream (many of them producing corn on an unprecedented scale in response to US ethanol subsidies) will have increasingly competing interests.

Also, as the article briefly mentions, nuclear power, by far the largest zero emmission electricity resource in the US, could also be significantly affected by decreases in fresh water availability. The average reactor needs more than 830 gallons of freshwater per megawatt hour for cooling purposes. While much of this water is then returned upstream, it exits significantly warmer than it went in. Thus, not only does the amount of water available matter, the temperature does too. As Greenwire reported, on Aug. 16, water temperatures in the Tennessee River hit 90 degrees Fahrenheit at Athens, Ala., forcing the partial shutdown of reactors at the Browns Ferry Nuclear Plant.

I guess I don’t really have a big point or conclusion to make right now. Just wanted to highlight an important complexity in the policy debate about the effects of climate change, one that demonstrates the Bayesian nature of the problem.

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One Response to “Spillover”

  1. Daniel Hall said

    Another complicating factor that the NYTimes Magazine piece doesn’t spend much time discussing is the use of river flows for species protection. Endangered species listings are another major element in western water allocation decisions. Some dams, for example, are now operated in a “run-of-river” fashion, attempting to simulate the natural flows that would occur most of the year. This can decrease the capacity for generation, or at least impact the value of generation by preventing dam operators from dispatching hydropower without taking other considerations.

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