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Interested in Water and Forests?

Go read Andrew Walker’s post “Wishful Thinking About Forests and Water” over at the excellent New Mandala blog.

Andrew’s work tends towards the hard science approach – measuring water flows in the dry season, comparing it to forest catchement systems and hydrology regimes, and making measured conclusions. All good stuff, and desperately needed in a period where we tend (myself included) to go all Henny Penny about the environment.

I have reservations about the argument being advanced here, but no justification or qualification to oppose them. For the most part I’m simply glad that people are doing this work. I would like to see future work on forests and hydrology regimes take on some larger regional questions, however.

For instance, when Andrew writes that decreased forests do not necessarily equal decreased dry-season flows (as you would expect, given the traditional understanding of forests as water-retention devices, which expend their wet-season accumulations during the dry), we are not given any real understanding for what actually accounts for this. (Again, not his point in the paper – but an important project for the future perhaps). He says that dry season flows may actually increase! Where is all this water coming from?

One possible source is hinted at, but not connected in the post or the paper itself – deforestation has not resulted in lowered rainfall. But rainfall is not (especially in monsoon Asia) merely the result of forest hydrology, right? (right?) Are we dealing here with a much larger cycle that is potentially fouling up the local data on forest hydrology and dry-season water flows?

Anyway, you’d do a lot worse than taking a careful read of Andrew’s excellent work.

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2 thoughts on “Interested in Water and Forests?

  1. Andrew Walker says:

    Hi Erik, thanks for the comments. I think the issues you raise are, by and large, dealt with in the paper I refer to. Of course, there is considerable uncertainty and on key points and I have tried to capture that uncertainty in the paper. To answer the main point above very simply: deforestation can increase dry season flow because trees use (via evapotranspiration) a great deal of the water that falls in the wet season. A lot of the water that soaks into the ground is pumped out again by the trees. Deforestation means that less of this water is pumped out and more is left in the ground to supply streams during the dry season. But there are lots of “ifs and buts” and these are discussed in the full paper. Of course, I am not advocating deforestation to increase dry season flow! As I argue in another paper on the “politics of hydrology” (there is a link to it from the NM Bloggers page over at New Mandala) the key issue is irrigation water demand not water supply.

  2. Erik says:

    Hi Andrew – (I’ve been away at a conference, or would have responded sooner). I’m sure that many of the issues are indeed addressed in the paper, and this points to one of the problems with such a public discussion of technical problems – I’m not a hydrologist, and although I have a more than passing interest, and have achieved a higher than average (person’s) knowledge on water systems, I’m nowhere near the competency of those trained in the field.

    I’ll be following future discussions closely, and will continue to attempt to educate myself on the matter (including checking the paper you referenced above), and am not confused about your lack of advocacy vis-a-vis deforestation.

    With all those caveats, let me rephrase (if you’re still reading!) my concern, which is less of a concrete question than an attempt to understand what your paper’s conclusions mean in a broader context.

    I am much more concerned with larger ecological systems and the role irrigation and agriculture play in transforming them than I am in the role of these same ecozones in serving agricultural needs, such as the need for dry-season irrigation. One reason for this is that water doesn’t transform itself magically (or even with the massive input of labor) into a sufficient amount of rice and crop for food and commodity sale. Human societies have multiple and complex sets of relationships to their environment, including (at the level of subsistence provision) the need for forest forage, water supply (perhaps independent of forests), etc. So while I agree that from a traditionally agronomical point of view water demand is a central concern, treating it as the sole concern for rural rice-growing communities risks blinding us to the other transformations that take place.

    Obviously, this is not the same concern that you have in your paper, and it would be foolish of me to insist that we share our concerns in all research. I’m only attempting to understand (with my limited technical knowledge) how to situate your findings in relationship to my own concerns.

    Cheers, and thanks!

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