This is a nice clear piece on system re-op. Whenever you hear someone say ‘system re-op’, this is basically what they mean. After you read that, come back to talk about water modeling.
Andrew Sullivan thought Dr. Lund’s analysis of a dry climate hydrology stood out of the longer article on California water.
Even with the worst conceivable climate change, the kind of global warming that brings 70-year droughts to California, the state might do okay.
That seems counterintuitive, but that’s what Jay Lund, who heads the UC Davis Center for Watershed Sciences, loves about his model of the state water system, CALVIN. He and his colleagues ran a range of climate scenarios through CALVIN, asking for a look at what very dry, very warm scenarios might do to the state’s water system out to the year 2100. The results were shocking.
Basically, in CALVIN’s rendering of the future, the state’s economy is fine. “It was amazing how little the damage was to the state’s economy,” Lund said. …
Agriculture does not fare quite as well, but the state’s agricultural production only falls 6 percent. That’s despite increasing urbanization of agricultural land and, in the driest scenario, a 40 percent reduction in water deliveries to the Central Valley. “The farmers are all smart people and they’ll cut back the least profitable stuff,” Lund said. They’ll also fallow land, according to CALVIN—roughly 15 percent of the irrigated parcels currently farmed today, or 1.35 million acres.
I am sure that’s what CALVIN said, but you have to understand what CALVIN does to interpret it. (Dr. Lund, I know you stop by. Apologies if I don’t get this right.) CALVIN is an optimization model; when it does a run, it is hunting for the best possible outcome it can get by following the rules of its reservoirs and canals and fields and cities. Even more important, CALVIN knows the entire what, ninety? years of its hydrology all at once. It has perfect foresight. So basically, when it starts optimizing, it can look forward in 2012, see that the next two years (2013, 2014) are dry, and stash all the water it can. It also doesn’t have to hedge on whether to empty reservoirs before a flood; it knows whether a flood is coming. If there are no floods coming, it doesn’t have to empty reservoirs and can hold tight to stored water. When you know your hydrologic future, you can do a lot to store or release water smoothly.
I am not telling you anything shocking about CALVIN; all the modelers know this. But the best outcomes out of CALVIN include something we don’t have, which is specific, detailed knowledge about the hydrology in the future. When I see a surprisingly good outcome from CALVIN, I generally take that as the most optimistic case. Sure, we could do that well if we are perfect optimizers who know the future. Then I mentally adjust for being not-perfect optimizers who don’t know the future and figure our real life results will be somewhat worse.