For those of you interested in the sometimes arcane debates that occasionally break out on New Mandala on the relationship between forests and catchment hydrology, here is an interesting article. It examines the relationship between land cover, soil moisture and run-off in the Mekong basin. The results are based on a “macro-scale hydrologic model.” I won’t go into all the details – much too boring – but one of the main conclusions is worth quoting:
Simulated soil moisture shows an important relationship to vegetation type: It was in general highest for agricultural areas; and lowest for grassland and woodland areas-except when antecedent precipitation was high (as is the case immediately following the rain season), when soil moisture was the lowest for forested areas. Thus, the vast forest to agriculture conversion that took place in the second half of the twentieth century was likely accompanied by an increase in soil moisture levels. Such an increase is exacerbated in those agricultural areas that are irrigated or where runoff is retained by bunds. (page 1745, my emphasis)
Why is this important? Who cares about hydrological modelling?
It is important because farmers, especially farmers in upland areas, are often unfairly blamed for causing hydrological problems (water shortages in particular) when they clear forested areas for agriculture. There is a persistent mythology within the region (and elsewhere) that forest clearing produces desication. The findings of this particular study add to the large body of good scientific evidence that this a highly misleading interpretation of complex catchment processes. Sub-soils can be wetter in agricultural areas because many forms of agriculture use less water than forests. And, as the quote above indicates, farmers often use a range of practices to encourage water to soak into agricultural soils.
Blaming hydrological problems on deforestation is easy because it is consistent with conventional wisdom. But it is often inaccurate.
7 responses so far ↓
1 nganadeeleg // Jul 9, 2008 at 7:51 pm
I do not wish (nor am I qualified) to comment on whether farmers are unfairly blamed for causing hydrological problems when they clear forested areas for agriculture, but I would be interested to hear whether you are merely defending the farmers against what in y0ur view is unfair criticism, or are you advocating for more deforestation?
2 SiamCollective // Jul 10, 2008 at 10:32 am
very intresting story. but I wonder the land included in these test are lande that cultvated พืชไร่ or พืชสวน cuz I’ve heard lot that land growing พืชไร่ will be less moisture than the latter.
3 Grasshopper // Jul 10, 2008 at 10:55 am
Yes I agree with nganadeeleg, your argument allows for logging advocates to add further justification to their position.. I am reminded of this: http://rspas.anu.edu.au/rmap/newmandala/2008/06/20/nam-theun-resettlement-an-entirely-predictable-stuff-up/
What is your position on deforestation?
practices to encourage water to soak into agricultural soils. But what about non-agricultural soils? Or is farming the only importance? Do these farmers care about what they don’t cultivate for currency? You’ve argued strongly that the farmers care about voting and politics, so I should trust that they are equally concerned with the environment that is not financially beneficial to them.
4 Andrew Walker // Jul 10, 2008 at 12:10 pm
I will respond with a passage from Hamilton and Pearce that we quote on pages 11-12 of Forest Guardians Forest Destroyers:
What the quote is indicating is that there is enormous diversity in land-cover change and that this diversity is obscured by emotive and blanket terms like deforestation.
So to ask someone what their position is on deforestation is a bit meaningless. It depends.
Whether or not a particular form of landcover change is desirable or undesirable will depend on a wide range of locally specific factors. Decisions should be informed by open-minded science and locally grounded research not by simplified narratives of environmental crisis.
And, yes, of course farmers in the region have a wide range of practices aimed at various forms of environmental protection. We describe some of them in our book.
5 Grasshopper // Jul 10, 2008 at 12:39 pm
Thanks for the quick response, I’ll buy your book. I thought after I commented that the word ‘deforestation’ was a bit ambiguous.
6 jonfernquest // Jul 10, 2008 at 4:46 pm
“Who cares about hydrological modelling?”
Everyone should care a lot more about it.
Historically water supply determines farming possibilities,
e.g. flood farming in delta areas, which determines
food supply, which determines carrying capacity of land,
which determines manpower mobilizable for warfare,
which determines whether a state will survive and expand,
one reason why flood farming Mons may have ceased to exist
as independent political entities, being absorbed into the rising
Burmese and Ayutthayan states.
Hydrology is still important, though differerently, since water supply has been one of the main constraints on increasing rice production during the ongoing food crisis.
Basic hydrology should be a fundamental part of the Southeast Asian studies curriculum.
7 jonfernquest // Jul 11, 2008 at 3:03 pm
The drought in Australia, cited as the cause of temporarily high rice prices in Thailand by Thai food economist Dr. Ammar Siamwalla, a couple of months ago, is another good reason why basic hydrology for everyone might not be a bad idea.
Today’s Australian drought news:
http://news.bbc.co.uk/2/hi/asia-pacific/7499036.stm
http://www.reuters.com/article/latestCrisis/idUSSYD170905
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