Could California weather a mega-drought?

Source: National Resource Conservation Administration

Source: National Resource Conservation Administration

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.

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,

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.


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15 Responses to Could California weather a mega-drought?

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  2. Tim says:

    Interesting speculation and modeling. Since agriculture is responsible for over 80% for the state’s water use and contributes less than 3% of its income, of course the state as a whole would be expected to suffer minimal economic impact, much less than states where agriculture is the main economic driver. Over the last 4,500 years there have been at least 78 major temperature/climatic changes that have impacted California’s central valley which seems to be the focus of this piece. In the prior droughts, the southern portion of the central valley stayed hydrated as evidenced by the survival of Tulare Lake where the largest trout could be caught until the advent of mass agriculture. As most know trout are temperature sensitive. Without huge impacts from agriculture the central valley weathered those previous droughts with minimal impact as evidenced by fish and wildlife survival. However, since the advent of the current, unsustainable agriculture, the lakes and riparian zones have been destroyed and the self-stabilizing features of nature have been defeated. Groundwater is no longer allowed to be replenished and the so called higher efficiency irrigation promises to all but eliminate groundwater recharge through irrigation causing further harm to the water environment. Lund seemingly ignores the great environmental damage that will result from a two-pronged attack posed by both agriculture and drought. It is this environmental damage that will more negatively impact California’s economy as water supply and quality are further damaged leading to greater disease and other social ills. Excessive and unsustainable agriculture is a disease that bodes ill for all of California.

    • jaylund says:

      In the paper we write more about the environmental effects, which are severe indeed. The model tries to meet as much environmental flow requirements as possible, before allocating water for other uses, but often there was just not enough water to do this.

      I was really surprised by how little damage might occur with such a horrible drought, if it were well managed. I expected the calculated damages to be much worse.

  3. Charles Raguse says:

    A very long (!) time ago (soon after I arrived in California in 1964), I would sometimes take a break from my duties as a brand-new faculty member in Hunt Hall’s Agronomy Department, and hike over to the campus library. A small table contained a frequently updated selection of “new books”. In one, the author(s) pondered the outcomes of a potential catastrophic drought. The over-arching conclusion was that history provided no evidence at all that a society that relied on irrigated agriculture had ever survived a major drought. Of course, the author(s) didn’t have computer models to “muddy the water”. I have always regretted not taking note of this small volume. Others, though, have written in similar vein. Note Henry Seidel Canby’s introductory comment on William Vogt’s “Road to Survival” (copyright 1948, William Sloane Associates, Inc., New York). There is much more needed for survival of societies in the face of overwhelming drought than can be provided by engineers and computer models.

  4. jaylund says:

    Of course. The hardest part is getting people organized to respond effectively.

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  6. i am very surprised to know, how little damage might occur with such a horrible drought

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