BrainiYak

The Vietnam War’s impact on hydrology in Laos

Guillaume Lacombe and his colleagues studied the effects of the Vietnam War on the Mekong River’s watersheds in Laos.

Citation

Lacombe, G., Pierret, A., Hoanh, C. T., Sengtaheuanghoung, O. and Noble, A. D., Conflict, migration and land-cover changes in Indochina: a hydrological assessment, Ecohydrology 3(4): 382–391. doi: 10.1002/eco.166 (December 2010)

Findings

The Institut de Recherche pour le Développment said of the study:

In the first area studied, as many bombs were released as in the whole world over during the Second World War.

This massive destruction of tropical forest was followed by recolonization of land by herbaceous or scrubby vegetation that had been less completely uprooted.

The whole process brought about a drastic reduction in average annual evapotranspiration and a substantial increase in runoff in that area: over 50% more between 1972 and 1975, then 15% more between 1975 and 2004.

The second study area, in northern Laos, experienced a massive exodus of its people: 730 000 to one million fled Laos . . . .

The land in the area had traditionally been cultivated, but once abandoned it was recolonized by forest.

The research team observed that the resulting rise in evapotranspiration and improved infiltration of water in the soil afforded by the regenerated vegetation brought a reverse trend, an average 30% decrease in runoff, between 1995 and 2004.

© 2010 Gayëlle Courcoux (editor) and Nicholas Flay (English translator), The Mekong, record of the Vietnam War, Institut de Recherche pour le Développment Scientific News Sheets (December 2010)

The bigger picture — the Mekong River hydrological results seem sensible to us, but would they make sense to researchers in the distant future who know nothing about the Vietnam War?

The Mekong study is a good example of how uncertainty pollutes what we would like to think we know.  The research team noted, in essence, that they had to guess about the causes of the runoff’s variability:

Although causalities could not be ascertained because of data limitations, these short- and long-term hydrological shifts were found to be consistent, in terms of occurrence, spatial distribution and magnitude, with the expected changes in the vegetation cover, either denser in the north (in response to abandonment of cultivated lands) or sparser in the south (as a result of bomb-induced deforestation and soil degradations).

Lacombe, G., Pierret, A., Hoanh, C. T., Sengtaheuanghoung, O. and Noble, A. D., Conflict, migration and land-cover changes in Indochina: a hydrological assessment, Ecohydrology 3(4): 382–391. doi: 10.1002/eco.166 (December 2010)

The Vietnam War was only about forty years ago, and we are already lacking data.

Looking forward, who knows what a research team just 2,000 years from now will make of whatever traces of our era the Mekong River leaves for them to find.

Now extrapolate our forty years of Mekong data uncertainty backward into climatological studies that scientists often want to sell as accurate.  Those studies generally use of proxy measures to hypothesize climatological conditions hundreds of thousands to millions of years ago.

The proxies, often biological and geological, take what we know of the present and ship it backward into contexts, where they arguably (a) do not belong or (b) would probably operate somewhat differently.  In regard to the indirect involvement of biological proxies, assuming evolutionary stability in their DNA and RNA seems absurd.

If forty years is enough to generate scientific uncertainty in some contexts, what should we expect of several million?

Tagged: bombing, Conflict migration and land-dover changes in Indochina, deforestation, depopulation, evapotranspiration, Gayelle Courcoux, Hoanh, Institut de Recherche pour le Développment, Lacombe, Laos, Mekong recored of the Vietnam War, Nicholas flay, Noble, Pierret, runoff, Sengtaheunanghoung