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So if it evaporates, as in the parent question, what does "requires 1 gallon of water" mean? One gallon goes back in the air, right? It will presumably end up a

So if it evaporates, as in the parent question, what does "requires 1 gallon of water" mean? One gallon goes back in the air, right? It will presumably end up as rain? So the net loss of water is 0, or am I missing something? Is there some loss that is permanent or slow to recover, here?

rb2k_ 12y ago
I guess the main problem is that the rain might fall somewhere else that is not California and we now have to move that water back there because otherwise they'd run out.
danjayh 12y ago
This would be true if they were actually getting rain, and they were using surface water, but that is not the case. They are in the middle of a drought, and they are using ground water, which replenishes very slowly.
thrownaway2424 12y ago
I don't think anybody is claiming that California's drought is due to a violation of the principle of conservation of matter, however rain that falls on distant lands is surprisingly useless.
fiblye 12y ago
It means that one gallon of water that could've been used elsewhere in California during the period of growth went into the clouds and is likely going to rain down a few thousand miles away. The point of the "n gallons of water per x fruit" is saying that one certain crop is incredibly inefficient with its water consumption, and it'd be better to use it on something else. It's like saying a bloated web browser consumes 500 MB of memory/tab. Your memory isn't gone forever after you use it, but so long as you're using that browser or growing that crop, it's draining that resource away from other applications. You probably only have 8-16 GB of memory to use at once, just like a region only has N gallons of water it can use at any one time.
analog31 12y ago
In a localized sense, the loss is of the water that's readily available for use in that region. I suppose you could think of it as a sort of "debt," where you measure the loss in terms of energy or dollars required to restore the water at the rate it's being consumed, for instance through desalination. I suspect it's just simpler to call it "loss of water." Another way to think about it, is that farming has historically occurred in places where there are decent natural growing conditions: Climate, soil, and water. If you let the water go somewhere else, through evaporation and rainfall, then you might end up having to maintain growing conditions artificially by bringing the water to where there is decent climate and soil. And again, you could measure the cost of doing that as a "debt."
vacri 12y ago
The water cycle has a net loss of 0, but only on a global scale. Water that is expired by a tree and ends up as vapour in the air does not precipitate straight out again, unless the air is already completely saturated (ie: it's already raining/snowing). That water will indeed come down again... somewhere. In general, something needs to change for the water vapour to turn into rain, like changing altitude from passing over a mountain (reducing temperature and pressure), or the air stream combining with a colder one. Deserts tend to be flat and featureless, so there's little in the way of atmospheric change as you pass through them. An interesting example of this is the continent of Australia - the most populated part is on a thin strip on the east coast as that's where the water and hence arable land is. But the air moves across the continent from the west - in general, the air crosses an entire continent before giving up it's water. It gives up that water because it hits the long strip of mountains slightly inland from the east coast, which changes the conditions appropriately. But until it hits those mountains, the entire overland journey is very consistent for the vapour, so it stays as vapour. There are several mechanisms at play here in dumping the water from vapour into rain - check out wikipedia, I couldn't do them all justice.
manicdee 12y ago
That gallon of water used to water that tree right now is not available to me to shower, drink, or flush right now. The water becomes immediately unavailable until it returns to the ground as rain somewhere or someWHEN else. Sure, looking at the big picture the water is never actually "lost". Until you can plumb my domestic water into the clouds directly, the big picture is irrelevant. All that matters is the water that is available in a potable form for me to drink right now. In financial systems, we might come to an arrangement that I will pay you Friday for a burger Tuesday. With water, it doesn't work like that. If I don't have water now at the time I need it, there is no use promising me water late next week. And when it comes to a decision between me having a litre of water today for me to survive on, or saving your thousand-dollar almond tree, I will unashamedly pick me.

rb2k_ 12y ago

I guess the main problem is that the rain might fall somewhere else that is not California and we now have to move that water back there because otherwise they'd run out.

danjayh 12y ago

This would be true if they were actually getting rain, and they were using surface water, but that is not the case. They are in the middle of a drought, and they are using ground water, which replenishes very slowly.

thrownaway2424 12y ago

I don't think anybody is claiming that California's drought is due to a violation of the principle of conservation of matter, however rain that falls on distant lands is surprisingly useless.

fiblye 12y ago

It means that one gallon of water that could've been used elsewhere in California during the period of growth went into the clouds and is likely going to rain down a few thousand miles away. The point of the "n gallons of water per x fruit" is saying that one certain crop is incredibly inefficient with its water consumption, and it'd be better to use it on something else. It's like saying a bloated web browser consumes 500 MB of memory/tab. Your memory isn't gone forever after you use it, but so long as you're using that browser or growing that crop, it's draining that resource away from other applications. You probably only have 8-16 GB of memory to use at once, just like a region only has N gallons of water it can use at any one time.

analog31 12y ago

In a localized sense, the loss is of the water that's readily available for use in that region. I suppose you could think of it as a sort of "debt," where you measure the loss in terms of energy or dollars required to restore the water at the rate it's being consumed, for instance through desalination. I suspect it's just simpler to call it "loss of water." Another way to think about it, is that farming has historically occurred in places where there are decent natural growing conditions: Climate, soil, and water. If you let the water go somewhere else, through evaporation and rainfall, then you might end up having to maintain growing conditions artificially by bringing the water to where there is decent climate and soil. And again, you could measure the cost of doing that as a "debt."

vacri 12y ago

The water cycle has a net loss of 0, but only on a global scale. Water that is expired by a tree and ends up as vapour in the air does not precipitate straight out again, unless the air is already completely saturated (ie: it's already raining/snowing). That water will indeed come down again... somewhere. In general, something needs to change for the water vapour to turn into rain, like changing altitude from passing over a mountain (reducing temperature and pressure), or the air stream combining with a colder one. Deserts tend to be flat and featureless, so there's little in the way of atmospheric change as you pass through them. An interesting example of this is the continent of Australia - the most populated part is on a thin strip on the east coast as that's where the water and hence arable land is. But the air moves across the continent from the west - in general, the air crosses an entire continent before giving up it's water. It gives up that water because it hits the long strip of mountains slightly inland from the east coast, which changes the conditions appropriately. But until it hits those mountains, the entire overland journey is very consistent for the vapour, so it stays as vapour. There are several mechanisms at play here in dumping the water from vapour into rain - check out wikipedia, I couldn't do them all justice.

manicdee 12y ago

That gallon of water used to water that tree right now is not available to me to shower, drink, or flush right now. The water becomes immediately unavailable until it returns to the ground as rain somewhere or someWHEN else. Sure, looking at the big picture the water is never actually "lost". Until you can plumb my domestic water into the clouds directly, the big picture is irrelevant. All that matters is the water that is available in a potable form for me to drink right now. In financial systems, we might come to an arrangement that I will pay you Friday for a burger Tuesday. With water, it doesn't work like that. If I don't have water now at the time I need it, there is no use promising me water late next week. And when it comes to a decision between me having a litre of water today for me to survive on, or saving your thousand-dollar almond tree, I will unashamedly pick me.