[rsj_hn]

> However, agriculture uses 80% of the state's water.

This is what economists sometimes call a stock-flow inconsistent argument. Water, like money, circulates, and to stick your finger on one part of that chain and insist that something is being used by X and thus not available for Y does more to obfuscate than enlighten. Some of the water "spent" on agriculture then evaporates into the air and ends up as snowfall where it is "spent again" on skiing, and then it melts and travels down a river and lands in hetch-hetchy where it is "spent" on someone in San Francisco taking a shower. Things like subsidies matter, government's role in diverting water from A to B matters. But just as more rains fall on rural areas than urban areas, you will see more water used to support agriculture than to support cities. That does not mean that anyone is taking away anyone's else water and using it up for some nefarious purpose.

[btilly]

You may be overestimating the effects of circulation of water.

It is true that water that evaporates is likely to someday fall somewhere as rain or snow. However agriculture is going to spread a lot of water during summer. At that point it evaporates very efficiency. But unfortunately during summer it is unlikely that anywhere in California will have the conditions for rain, so that water is going to fall in some other place. Normally Colorado, from which it is unlikely to go back into California.

So from the point of California, water used in agriculture is gone. Not to be seen again any time soon.

[rsj_hn]

Well, yes, water doesn't respect state boundaries so I'm not claiming that California is a closed system, nor am I claiming the majority of water used in agriculture evaporates rather than going into the water table. But just as water evaporates in CA and lands on Colorado, so water evaporates in the pacific and lands on California, and we get ground water and river water back from Colorado. So are you claiming there is some systematic net movement of water out of California and into other states/countries? That would require presenting an entirely different set of facts than has been presented here.

[btilly]

As irrigation becomes more efficient, the majority of water used in agriculture does indeed go to plants and then to evaporation. And while California does get some water back from the Colorado river, most does not. The water coming to California from other sources, such as the Pacific, is not materially affected by the amount of water flowing into the Pacific from California.

Therefore water given to California agriculture in any given year is unlikely to come back to California within that year. So for planning purposes, water given to agriculture should be considered mostly consumed and available to no other use within California.

And as the climate becomes hotter, this becomes even more true. A hotter climate means faster evaporation and an easier time for it to blow over the Rockies. Which is part of the reason why the trend as the climate changes is for land to the west of the Rockies to become ever drier, while land to the east to become wetter. (Most of the water to the east comes from the Gulf of Mexico.)

[carlob]

> So are you claiming there is some systematic net movement of water out of California and into other states/countries?

Not OP.

The argument made in Cadillac Desert is pretty much the opposite: in order to irrigate California and to give drinking water to its inhabitants, we have damned and diverted many rivers elsewhere with some very large ecological effects.

Another thing to take into account is the salinization of soil as an effect of irrigation: every time water evaporates it leaves behind a salt deposit. This is a process we don't know how to revert and it's considered to be an important historical factor in the rise and fall of civilizations, migration patterns etc.

[kosh2]

> Water, like money, circulates

I'm not an expert in this area but I have strong doubts that this argument is useful in this case.

Let's think of an example. Two people are die because of dehydration. Luckily they happen to find a full 1 liter water bottle.

One of the them quickly grabs it and drinks it all. Then she tells the utterly shocked other person: "Don't you worry, water, like money, circulates. You see, I will eventually pee out this water and it will evaporate and it will become rain and so on".

My point is, that the amount of usable water matters. If you have X liters of waters from wells, rivers and so on each year that you can access, it won't be any more just because there is a water cycle.