Could CA Weather a Mega-Drought?

By Jay Lund.

In the past 1,200 years, California had two droughts lasting 120-200 years. Could the state’s water resources continue to supply enough water to drink, grow crops and provide habitat for fish with such an extreme, prolonged drought?

With careful management, California’s economy in many ways could withstand such a severe drought. That’s not to say some ecosystems and communities wouldn’t suffer catastrophic effects.

The UC Davis Center for Watershed Sciences explored this question a few years ago using computer models. We constructed a drought similar in scale to the two extreme ones found in California’s geological and biological records of the past 1,200 years (Harou, et al. 2010). We created a virtual 72-year-long drought with streamflow at 50 percent of current average rates, with all years being dry, as seen in the paleo-drought record.

We then explored the simulated drought using a computer model of California water management that suggests ways to minimize the economic costs of water scarcity for populations and land use in the year 2020.

Not surprisingly, the model results showed that such an extreme drought would severely burden the agriculture industry and fish and wildlife, and be catastrophic to some ecosystems and farm towns. The greatest impacts would be felt in the Central Valley.

However, if well managed, such a mega-drought would cause surprisingly little damage to California’s economy overall, with a statewide cost of only a few billion dollars a year out of a $1.9 trillion-a-year economy.

The key to surviving such a drought lies in adaptive strategies such as water trading and other forms of water reallocation. These strategies would be essential to improving the flexibility of California’s water supply and demand system during such a prolonged drought.

Interestingly, most reservoirs we have today would never fill during a decades-long drought, so expanding surface storage capacity would be futile.

California has a very flexible water supply system that can support a large population and economy under extreme adverse circumstances — provided it is well managed.

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Jay Lund is a professor of civil and environmental engineering and director of the Center for Watershed Sciences at UC Davis.

This article originally ran April 12, 2011. Some figures and text have been updated.