A Glimpse of California's water future

By: TIM BARNETT - Commentary | Saturday, February 23, 2008 7:58 PM PST ∞

The idea of global warming is an abstraction to most folks. However, very shortly we who live in Southern California will get a first-hand demonstration of just how it will affect our lives.

The Achilles' heel of Southern California, indeed the whole Southwest, is water. We in San Diego get our water from two main sources. The primary source is the central and northern parts of our state. The other source is the Colorado River. Water from these two sources has enabled the growth of our local civilization and economies. We take these two sources for granted, but just how reliable are they? It turns out, not very reliable at all.

About 0.8-1.7 million acre feet of water, enough to support about 6 to 12 million people, comes into the Los Angeles Basin every year from the north. The water's long journey starts in the snow pack of the Sierra Nevada, travels through the Sacramento Delta and then via aqueduct to Los Angeles where the Metropolitan Water District dispenses it to the region, including San Diego.

In a warmer world there will be less snow and what snow there is will melt earlier. The Sierra, which has been our water banker, will go out of business or at least be seriously impaired. This trend, toward less snow and earlier river flow, has recently been documented by rigorous scientific studies. The water climate of California is already changing and will only change more in the future.

The Sierra source also has been threatened because the pumps that carry the water from the Sacramento Delta have also been killing the federally protected delta smelt, an endangered species, and who knows what else. A judge has ordered a temporary curtailment in pumping water from the delta by over 500,000 acre feet to protect the smelt. Compare this number with the amount of water delivered to Los Angeles.

That's not the only problem. The delta has other endangered, protected species as well. As the snow pack dwindles under the impacts of global warming, there will be less fresh water available in the summer to dilute the sea water influx from San Francisco Bay and the delta will become saltier. A number of protected species will be impacted. It may be necessary, by law, to release what small supplies of fresh water remain to protect these creatures.

The Colorado, the second source, provides Southern California 4.4 million acre feet of water each year, about 1.0 million acre feet of which goes to non-farming use. But the Colorado water is already oversubscribed. In fact, each year over 1 million more acre feet of water are taken from Lake Mead than are supplied by Colorado River inflow to the lake.

This overdraft alone would draw down the reservoirs on the Colorado to dead pool levels within a decade or so. The impacts of global warming are intensifying the problem, for our climate models and observations show that less water will be supplied to the Colorado system, hastening its demise.

Just-released studies show these reductions will lead to lakes Mead and Powell going dry by 2021 with a 50 percent probability, in other words, a 50-50 chance the Colorado System storage will be gone in just 13 years, and a one in ten chance it will be exhausted by 2014.

So Southern California's two main water sources will almost certainly be heavily impacted by global warming. Bottom line is that water will become more expensive and scarce in our near-term future if we do nothing but stay the course.

What can we do about these coming water crises?

First, the bad news. These impacts will be on us before we get any relief from reduction in atmospheric greenhouse gases. The planet would continue to warm for some decades even if we held fixed carbon emissions at today's values immediately. So our actions must first be toward adaptation.

Now the good news. We have many options available right now to help stabilize the situation and sustain the Southwest as we know it, at least for a few decades.

One option is start a serious water conservation effort and that includes the judicious use of recycled water. More dams in California, if we can squeeze them in, will catch the snowmelt we have to pass through our reservoirs systems due to their lack of capacity, thereby partially replacing Mother Nature's role as water banker. (Ditto with subsurface sequestration of water.)

We can shift water between agriculture, which uses 70 to 80 percent of it, and thirsty urban populations. San Diego and other cities have already started this process. This will mean fallowing less productive land, but growing subsidized crops with subsidized water has never made much sense anyway.

Desalination is also an obvious solution, as long as it does not require fossil fuel to run the desalination plants.

Another option is to seriously curtail the run away building boom that has succeeded in building communities in our deserts without thought to the stability of their water supply.

These actions, and others like them, will buy us some time. But in the not too distant future, we will have to figure out how to get by with less water than we have today. This is especially true of the Colorado source which could lose up to 30 percent of its flow within 30 to 40 years.

That loss would be equivalent to the total supply of water that Southern California takes from the Colorado in a year. Maybe by then, we will have stabilized carbon emissions and brought the greenhouse warming to a near standstill. Whether that happens or not is totally up to us, the present inhabitants of Planet Earth, not the next generation. That means it is up to you and me!

Tim Barnett is a research marine physicist at Scripps Institution of Oceanography at UC San Diego.

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