Azara Blog: When the rivers run dry

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Date published: 2007/02/21

The second lecture in the Department of Engineering's Fifth Annual Lecture Series in Sustainable Development (2007) was given by Fred Pearce, a journalist from New Scientist, on "When the rivers run dry".

The lecture seemed to consist mainly of an endless stream of statistics about water supply and demand on the planet. Of course there is no point talking about something in a "sustainable development" series if you couldn't claim that the world was in deep trouble, and that was indeed the claim here. Forget about our carbon footprint, what we should be worrying about just as much is our water footprint.

So it seems that the average UK citizen drinks about 5 liters per day, and directly consumes about 150 liters of water per day (for flushing the toilet, washing, etc.). However this is dwarfed into insignificance compared to the water that is used in the creation of the goods that the UK imports. Pearce claimed that the average UK citizen indirectly consumes around 4000 or 5000 liters of water per day. This is mainly for agricultural goods (food and cotton). Apparently someone has decided to label this indirect consumption by the name of "virtual water".

Pearce claimed that the world could "sustainably" consume around 4000 liters of water per day. So the UK is just over the limit of what was "sustainable" if all the world consumed water at the UK level (which of course it does not).

Apparently (so says the UN) it takes around 500 liters of water to produce a kg of potatoes, 1000 liters for a kg of wheat, and 2000-5000 liters for a kg of rice. And around 11000 liters to produce the feed for cows to produce enough beef for one hamburger. Well, these figures are no doubt not that accurate, but they are quite amazing none the less.

The problem these days is that so much available water is being used to produce agricultural goods that many rivers are running dry, at least for much of the year. Apparently two thirds of the world water supply is used for irrigating crops. And this does not just affect the developing world. America is the world's biggest exporter of agriculture, and Pearce said that these exports account for about a third of US water consumption.

Back in the good old days, in the 1960s and 1970s, a lot of the doomsayers claimed that not only would the world population double (which it has) but it would not be able to increase its food supply to match so that billions of people would die of starvation. Well the doomsayers were wrong about that one. There was a "green revolution" where better crop yields were achieved. Apparently these new crops could produce twice the food per acre but have used three times the water (never mind energy).

Of course most people these days worry about carbon emissions, but some worry about water, and it is often claimed, as Pearce did, that many of the major wars this century will be about water, not land or oil.

Well what is there to do. One option is to desalinate sea water. Another option is to build more storage areas (i.e. build dams) to protect against droughts and dry seasons, although this is controversial. Another option (which seems crazy) is to move water from where it is plentiful to where it is not. Another option is to use water more efficiently (it seems that a lot of water used in agriculture is wasted, mainly because it is not priced correctly). Another option is to have a "blue revolution" where crop varieties were bred to require less water. Some combination of these options will be forced on the world, since you cannot do without water, and the world population is still increasing.

Even in the UK we need to worry about our (direct) consumption of water, especially in the dry south-east. Pearce pointed out there were ways of re-using water that were not commonly done yet, and that the government should consider tightening the building regulations on this front, given how many houses it wants to add to the south-east. And many UK houses do not have water meters (so just pay an annual flat fee to cover their water consumption, independent of how much is actually consumed).

In the question and answer session, someone pointed out that if you take the figures that Pearce provided at face value, then whatever the UK does in its own backyard is largely irrelevant, since our direct (i.e. internal) water consumption is dwarfed by our indirect (i.e. external) water consumption. Pearce didn't seem to understand the question and didn't answer it.

Someone asked, in that regard, whether we should all be eating more British-grown food instead of imported food. At this point Pearce then admitted that the whole basis of calculating the water cycle was very complicated and it was difficult to actually do the sums properly. In particular, for example, all the water that is used to grow some crop is not lost to the planet, it just (possibly) ends up in differing locations to where it once would have gone, and perhaps more polluted.

As a related example, he said that in France the per capita water consumption was relatively high because it included the water needed to cool all their nuclear power plants. But most of that water was not lost, it just went back into its original source (somewhat warmer, which is a different problem). And some water used in growing agricultural crops might well have the same fate. Pearce said he could not quantify this issue, but of course it is crucial to understanding what the real problems are.

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