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For some perspective: LA county uses about ~50 Million cubic meters of water per year. The largest Israeli desalinization plant is ~225 Million cubic meters per year. The entire state of California uses ~50 Billion cubic meters of water per year. Very rough numbers

But only a few percent is for residential use, right? So ignoring agriculture, a few large plants should provide enough water for humans to be happy in Cali solely off of desal?

My take is, water is a commodity (mostly) in California. I'm a bit skeptical of residential users paying dear for desalinated water in order for agricultural users to have a larger share of the 'free' water.

I'm guessing people in Cali would not be very happy living without agriculture, so no.

California's GDP is estimated at 1,800 billion. Economic activity coming from agriculture is estimated at about 100 billion. Given an average economic growth rate of 2.5% per year for California, losing all agriculture would set California's growth back about 2 years.

Nobody wants to do that, and there are all sorts of complex legal issues around water rights. But push come to shove, California could survive just fine without its agricultural sector.

Agriculture brings may bring in only 5% of the state's economy, but if every single piece of food eaten in California had to be imported, it would cost a lot more then 5% of its economy.

If food were grown by magic, without employing any people, and it could all be sold at cost, it would contribute 0% to the state's economy. Does that mean that it would make economic sense to immediately stop growing all that food? Of course not! The fact that growing food is so cheap is a good thing!

To amplify your point, excepting water, the San Joaquin Valley in particular has the best climate and input factors in the possibly the world for producing high value crops at low cost and low environmental impact. If we could supply another 50-100M acre feet of water to the aqueduct system amazing thinks could happen.

My quick calculation is the biggest of these desal plants would only feed 25,000 acres of almonds. There are 1M acres +/- of almonds in California, if we wanted to double nut protein production in California (the leading global exporter of almonds) you would need about 50 of the plants described not just three.

Who wants to build the giga-desal plant to feed the Clifton Court Forebay?

There are numerous problems with how prices relate to both costs and value.

Pinch off ag in enough places, and you'll find it's got some underappreciated benefits.

The alternatives to crops being raised in Calfornia aren't limited just to the lost ag revenue, but to the expense of transporting in food, the loss of fresh fruits and vegetables (California specialises in "table" crops (vegetables), fruit, and grapes especially, knock-on effects of worsened nutrition and reduced food quality, price increases resulting from withdrawal of California ag land, etc.

Simply figuring out where you'd source that food from becomes problematic. Seattle is the only West Coast port with significant capacity and growing regions near it (Portland might do in a squeeze), plus growing area. There's no assurance that California crops, particularly greens and vegetables, would be suited to more northern climates and growing conditions, though adaptations might be made.

And there's considerable room for adjustment in California's crop mix. No need to grow alfalfa in the desert, as a perennial crop, that's easy to fallow in dry years. Tree crops are multi-decadal investments, and will not simply fail to bear fruit without water, but will die -- one of the real crimes of the almond-planting spree around the state. You lose cropping flexibility.

(There's a study I turned up some months back, either IRS or Federal Reserve, on tree crop asset lifetimes -- some bearing orange trees in Southern California are approaching or over 300 years old.)

A straight market-based analysis does poorly.

Everything that you say is correct. But given the choice between trying to maintain agriculture and guaranteeing working water taps, California should choose people.

At some point the choice is going to have to come down to not people.

Or at least fewer of them.

So does that mean ag or taps?

"Taps" == municipal water supplies.

That is: Not ag.

(Ag water generally comes from canals, irrigation districts, and in some cases pumps or aquifers.)

What I meant was, when you choose people, does that mean the convenience of potable tap water, or agriculture? I could argue both ways.

California can do that, but the demand for fruits and veggies will still be there. California grows the vast majority (in the US) of quite a few of those: peaches, carrots, strawberries, and others.

Instead these will need to be shipped from overseas by marine transport which is an intense source of pollution.

California only ended up with the majority of those markets due to the how federal agriculture subsidies are structured.

You can grow carrots and strawberries almost anywhere in the US. Peaches need things a bit warmer, but again most of the US is fine.

It makes sense to shift water intensive crop production to states with water.

And it is little appreciated that federal agriculture subsidies are structured the way that they are because maintaining food security was seen as necessary for the stability of our country.

To see why you have to go back to the Dust Bowl, and then the prospect of severe famines in Europe at the end of WW II. It turns out that if you have 10% more food than people need, food is cheap. But make that 10% less and food becomes very expensive, people starve, and you get political unrest.

> losing all agriculture would set California's growth back about 2 years

This is a superficial analysis. It assumes that California's agriculture could be easily replaced. Not to mention that whatever replaces it may face the same issue with desalination. In actuality the entire country is dependent on California agriculture to a large extent and "The loss of California’s output would create a dire situation for at least a decade."[1]

[1] http://www.slate.com/articles/health_and_science/explainer/2...

In general, it's a foolish idea for regions to give up agricultural capability because the fickle nature of international politics and economics means it is next to impossible to always guarantee food supply through trade.

What if your current comparative advantage gets lost due to development elsewhere? Your exports will no longer earn you the foreign currency you require to import food (look at Venuzvela for a recent example or the disaster of Haiti where IMF prescribed food imports or India's famines of the 1960s)

This is the reason nations heavily subsidize agriculture even when they can rely purely on imports.

To be clear, though, California's water usage would go down substantially if water became more expensive or scarce.

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