Bryan Lawrence : Bryan's Blog 2009/01/28

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Bryan's Blog 2009/01/28

Reading in 2009, 2: Water Supply

And so to "When the Rivers Run Dry" by Fred Pearce. Which is about what it says on the tin ...

Another apocalyptic read (I'm not in an apocalyptic mood, it just happened that I got two birthday presents last year in the same vein). This book reads well, but it's another one that could get you breaking out the whiskey before the sun gets over the yardarm. It's absolutely not a book about global warming! Although global warming gets a few mentions, it's a book primarily about good intentions going bad coupled with bungled engineering and short term thinking. It is scary precisely because it would appear we're stuffed on the water front before we even get to the implications of warming ...

There are some really fascinating bits in this book, the state of the Aral Sea for example, I guess I vaguely knew what had been going on, but the detail presented in this book is scary, not just because of what has happened, but it (the dry up) was planned that way (and despite all the planning, the resulting water for "use" is being frittered away).

Here are a few bits that I noted (for my own nefarious purposes, not because they were necessarily the most important or most interesting ...). All the numbers (except where stated) are from the book, I don't know what the original sources might have been.

Not enough water in the first place

A back of the envelope calculation (p33-35) of water availability goes something like this: we will run out of water unless we only use the water that falls as rain (somewhere), that is from the "fast water cycle". In practise we only care about that which falls on land (60K cubic km per annum). If we neglect that which evaporates, and that which is transpired (hmm, I'll get back to that), that leaves about 40K cubic km of runoff for "consumption. Of that hydrologists reckon it's practical to "capture" 14K (why?). Take out the runoff in inaccessible places (like Siberia), and we're left with 9K, or about 1400 cubic m per annum per person. But earlier on (p22) he's calculated that he himself consumes around 1500-2000 cubic m per annum in terms of water needed to feed and cloth him (as well as that directly consumed which is far less). So the bottom line is that if everyone wants to live like him, then there's a problem.

  • But we neglected the transpiration earlier on, and surely that's part of the water consumed to feed him? So I'm not so sure about the budget. However, whether or not he's got the budget details right, the actual efficiencies (or lack thereof) of actual hydrological systems that he discusses throughout the book make it clear that we have a major problem, and we're eating into water from the "slow water cycle" (deep acquifers etc, which are slowly, but surely, being drained).

We can feed them, but can we water them?

(p38) The UN FAO says that globally we now grow twice as much food as we did a generation ago, but we abstract three times as much water from rivers and acquifers to do so.

Dam them all

As a kiwi I both appreciate(d) the benefits of hydro power and mourn(ed) the losses from flooding ... but I always thought of dams as being a Good Thing (TM). However, it appears that it's not always that way: A World Commission on Dams (appointed by the World Bank) made some interesting observations in 2000 (p157-159):

  • Two thirds of all damns built globally for water supply to cities deliver less than planned (a quarter less than half)

  • A quarter of dams built to irrigate fields irrigated less than a third of the land intended.

  • Half produced significantly less power than advertised

    • an interesting number is the number of kw/flooded hectare: ranging from 0.2 to 5 for some examples he gives. I thought about that a bit: an interesting comparison is that a tenth of the area could provide between one and four times the same energy for the best of these (at 5-20 W/sq m - this last number from the synopsis - pdf - of a new book I want to read).

  • Even dams built to protect against flooding have increased vulnerabilities (because they're generally kept full and "emergency releases" are floods in their own right).

  • Dams have resulted in at least 80 million rural folks losing homes, lands and livelihoods!

  • Many have been poorly sited, often on the basis of faulty estimates of climatic flow (even in wealthy countries like the States: consider the poor future for the Colorado, and Lake Powell in particular - p223 and more recently).

  • and that's without considering silting and wetland removal etc

Water from thin air

On the positive side! Chapter 31 discusses technologies for "generating" water.

The discussion of water budgets above was about precipitated water. Of course at any given time a lot of water is sitting in the atmosphere as water vapour - roughly 98% of the 13K cubic km in the atmosphere at any one time (about six times the amount in the worlds rivers - again, at any one time).

There is a discussion of dew ponds, and artificial dew producers (using cold ocean water to cause condensation in the desert), and fog capture. Inspiring stuff. (He also talks about desalination and cloud seeding, both of which are rather less inspiring! Even if the former is widely deployed and/or necessary in some places, it's too energy intensive to be a "solution" to the global water issue.)

The bottom line

Actually, just like climate change, the water problem is not just a supply side problem, it's a demand problem too. In the final analysis, we need to drop demand, as well as address changing modes of supply. As far as the latter is concerned, there will be no one solution.

If I got one take home thread from this book it would be that there is a dire need for rational politicians and (more) sensible water managment practises, coupled with geographically realistic assessments of crop suitability. (And on the demand side, less cotton production - and consumption.)

Read it!

by Bryan Lawrence : 2009/01/28 : Categories environment climate books : 0 trackbacks : 3 comments (permalink)


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