Exporting green and leafy water

April 29, 2006 5:51 PM

Exporting green and leafy water. Agricultural exports, including fresh fruit and vegetables, are an important source of income for many developing countries, but they also threaten the evironmental future of those same producers. "Irrigated agriculture accounts for 70% of the freshwater used globally", while only a part returns to the environment. It isn't just in Africa; in India and in North America, all over the globe, water supplies are being stretched to the point of near breaking. [more inside]
posted by jb (12 comments total)

The Independent's article today was labelled "ethical shopping", and I'll admit that my first response was "Oh dear, I really shouldn't be buying imported vegetables if this is the case." of course, the next second I realised that would be a really bad idea - these are exports that are essential to economy of these countries, and my not purchasing vegetables from overseas would just mean they had less money. But is there something that can be done? Or is permanent environmental damage just inevitable? Is the trade of water possible? Maybe Britain could ship some of it's infamous rain to Kenya, in exchange for some green peppers and tomatoes - except that even Britain is running short on water these days.
posted by jb at 5:51 PM on April 29, 2006

GNN recently had a good article on the GIWA report: A new U.N. report on the world’s water makes for sobering reading. Why is no one paying attention?
posted by homunculus at 6:03 PM on April 29, 2006

How can a supply be stretched to the point of breaking? Talk about mixed metaphors.

Anyway, I don't exactly see how it's possible that the water is not returned to the environment.

It's not really the amount of water that is problematic, it's the rate of change of the amount of water, in other words the rate of water being used. If more water is used then comes in, then you'll see a problem, especially for the people downstream of you.
posted by delmoi at 6:07 PM on April 29, 2006

ChickenLittleFilter
posted by keswick at 6:12 PM on April 29, 2006

Well, one obvious way water is not returned to the environment would be what is discussed in the first link - that it has literally been exported to Britain - lettuce and other exports have a lot of water content.

There is also loss to evaporation in irrigated farming, where ground water or other sources which would be less susceptible to evaporation become more so when spread out across fields.
posted by jb at 6:17 PM on April 29, 2006

So, by 'not returned to the environment,' you don't really mean 'the environment.' You mean 'the geographic area where it was before it was exported in a given form.'

It's an interesting article. Water is one of the things that we modern folks in our paved-over glassed-in societies often forget that we depend on.

I'd say it's silly for humans to settle in arid places, but then I'd be calling myself silly (though I suppose I am).
posted by JekPorkins at 6:26 PM on April 29, 2006

Interesting topic.

From jb: these are exports that are essential to economy of these countries, and my not purchasing vegetables from overseas would just mean they had less money

Don't you think drinking water might be more important than cash? Plus, the high price fetched by exported coffee, bananas, sugar, roses is often a reason to either steal land from peasants or otherwise stop using agricultural land to grow food for the locals.
posted by salvia at 6:28 PM on April 29, 2006

The People's Daily brings great news from China !

The drop irrigation belt developed by the company costs only 5,250 yuan (634 dollars) per hectare of farmland compared with 36,000 yuan (4,353 dollars) for drop irrigation equipment developed by Israel, which boasts the most advanced drop irrigation technology in the world.

Wang Xingui, a farmer in Shihezi, has been using the drop irrigation under plastic film technology in the cultivation of cotton for four years.

He used more than 500 cubic meters of water to irrigate one mu (0.067 hectares) of cotton in the past, he now uses only about 200cubic meters. Moreover, his per mu cotton output has increased from 200 to more than 300 kg. He earns 170 yuan (20.5 US dollars) more per mu of cotton than in the past.

Also the prices make my head spin, spin spiiiin !
posted by elpapacito at 6:29 PM on April 29, 2006

Environmental Working Group found taxpayers subsidize California's Central Valley farmers to the tune of $416 million a year. Twenty-seven large farms themselvese received more than $1 million in subsidies apiece. Paying 2% of the cost / gallon that LA residents pay kinda kills the incentive to switch to drip irrigation, huh? Growing rice in the desert.....
posted by salvia at 6:36 PM on April 29, 2006

kinda kills the incentive to switch to drip irrigation, huh?

Yeah on short term it does, but if you put the same incentive in drip-alike-system it will pay itself and generate more revenue and be eco-friendly. Obviously you need somebody with an education and which isn't just stealing money...mhhh..not in the private sector I fear.
posted by elpapacito at 6:44 PM on April 29, 2006

In the last two years, scientists have also come to appreciate a new type of climate changing phenomenon -- global dimming. This is the result of solid pollutant particles thickening clouds, obscuring the amount of sunlight reaching the earth's surface, and effectively and significantly lowering the rate of evaporation of water from the oceans.

It's directly borne out worldwide as the major explanation for the observed drop worldwide in the pan evaporation rate. From the BBC program linked above (also recently aired in the U.S. as a Nova episode on PBS):

"PROF GRAHAM FARQUHAR (Australian National University): It's called pan evaporation rate because it's evaporation rate from a pan. Every day all over the world people come out in the morning and see how much water they've got to add to a pan to bring it back to the level it was the same time the morning before. It's that simple.

NARRATOR: In some places agricultural scientists have been performing this rather dull daily task for more than a hundred years. PROF GRAHAM FARQUHAR: The long-term measurements of pan evaporation are what gives it its real value.

DR MICHAEL RODERICK (Australian National University): And the fact that they're doing the same thing day in day out with the same instrument.

PROF GRAHAM FARQUHAR: Yeah, they deserve a medal. Each of them.

DR MICHAEL RODERICK: Yeah.

NARRATOR: For decades, nobody took much notice of the pan evaporation measurements. But in the 1990s scientists spotted something very strange, the rate of evaporation was falling.

PROF GRAHAM FARQUHAR: There is a paradox here about the fact that the pan evaporation rate's going down, an apparent paradox, but the global temperature's going up.

NARRATOR: This was a puzzle. Most scientists reasoned that like a pan on the stove, turning up the global temperature should increase the rate at which water evaporated. But Roderick and Farquhar did some calculations and worked out that temperature was not the most important factor in pan evaporation.

DR MICHAEL RODERICK: Well it turns out in fact that the key things for pan evaporation are the sunlight, the humidity and the wind. But really the sunlight is a really dominant term there.

NARRATOR: They found that it was the energy of the photons hitting the surface, the actual sunlight, that kicks the water molecules out of the pan and into the atmosphere. And so they too reached an extraordinary conclusion.

DR MICHAEL RODERICK: You know, if the pan is going down then maybe that's the sunlight going down. NARRATOR: Was the fall in pan evaporation in fact evidence of Global Dimming? Somewhere in the journals, they felt, must be the hard numbers that could tie the two things together.

DR MICHAEL RODERICK: And then one day, just by accident, I had to go to the library to get an article out Nature. As you do, I couldn't find it. And I just glanced at a, through the thing, and there was an article called Evaporation Losing Its Strength. Which reported a decline in pan evaporation over Russia, United States and Eastern Europe. And there in the, in the measurements, they said that the, the pans had on average, evaporated about a hundred millimetres less of water in the last thirty years.

NARRATOR: Mike knew how much sunlight was needed to evaporate a millimetre of water. So he put the two sets of figures together - the drop in evaporation with the drop in sunlight.

DR MICHAEL RODERICK: And so you just do the sum in your head. A hundred millimetres of water, less a pan evaporation, two and a half mega joules, so two and a half times a hundred is two hundred and fifty mega joules. And that is in fact what the Russians have measured with the decline in sunlight in the last thirty years. It was quite amazing.

NARRATOR: It was the same with Europe and the USA. The drop in evaporation rate matched exactly the drop in sunlight reported by Beate Liepert and Gerry Stanhill. Two completely independent sets of observations had come to the same conclusion. Though it seemed incredible, there was no doubting Global Dimming now.

DR BEATE LIEPERT: All of a sudden you see, oh my God the world is dimming, and then you, all of a sudden you see oh my God this really has a tremendous impact.

PROF GRAHAM FARQUHAR: There had to be dimming in Europe in America and in Russia, this is on a global scale. And we thought, this is really important because the amount of dimming was enormous. So this is BIG on a global scale."

I highly recommend interested people read the linked article, and see the program if possible. Truly scary stuff, more so because it is apparently a very good fit explanation for many pieces of alarming trend data about the Earth's rapidly changing climate.
posted by paulsc at 7:24 PM on April 29, 2006

Sounds like the age of aquarius to me.
posted by benjonson at 8:55 PM on April 29, 2006