Could California weather a mega-drought?

Source: National Resource Conservation Administration
Source: National Resource Conservation Administration

By Jay Lund

“Mega-drought” has become a frightful “thing” in public and media discussions.  In the past 1,200 years, California had two droughts lasting 120-200 years, “megadroughts” by any standard. 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 today?

Clearly, some ecosystems and rural communities would be devastated by such a drought, and it would certainly affect all California residents.  But with careful management, California’s economy in many ways could substantially withstand such a severe drought.

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 rural 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 $2+ 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 (yes, NEVER) fill during a decades-long drought.  So expanding surface storage capacity for managing megadroughts 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.

In adapting to the climate warming and changes that are upon us, the most important thing for California is to be well-organized and led for effective water management.  Panic or complacency generally lead to poor decision.  Good management of such a complex system will require serious and reasoned analysis and discussions, plus a political will to make reasoned decisions, even when ideal solutions do not exist.

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

This article originally ran April 12, 2011. Some text has been updated,

Further reading

Harou, J. J., J. Medellín‐Azuara, T. Zhu, S. K. Tanaka, J. R. Lund, S. Stine, M. A. Olivares, and M. W. Jenkins (2010), Economic consequences of optimized water management for a prolonged, severe drought in California, Water Resources Research46, W05522, doi:10.1029/2008WR007681.

MacDonald, G.M. (2007), Severe and sustained drought in southern California and the West: Present conditions and insights from the past on causes and impactsQuaternary International, 173-174: 87-100.

Stine, S. (1994), Extreme and persistent drought in California and Patagonia during medieval timeNature, 369, 546–549, doi:10.1038/369546a0.

About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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