Sunday, June 3, 2012

Perfect Alembics

Although tomes have been written on the antiquity of forest conservation in the Western Ghats, little has been written about its relation to water resources. An early discussion on that topic began with a series of essays prompted by Edward Balfour and his contemporaries. Thanks to a volunteer librarian on Wikipedia, I found the original and extracted the pages, here OCR-ed, except for some tables. This was part of what is termed as the "deforestation-dessication" debate.

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There are several factual errors (for example the description of pitcher plants) in these articles but one has to keep in mind the time that this came from. Here were adminstrators who were sincerely concerned about the effects of deforestation on water availability. The debate was on whether the flow in the rivers of the Western Ghats would be affected by deforestation. One school of thought considering that it might merely regulate flow and another that considers the trees on the mountains to actually have a role in harvesting water from the atmosphere by condensation. I suspect that not enough attention has been given to the latter although my understanding of Indian hydrology is too limited. In running a few searches on the Internet I found little recent Indian work on the subject and most authors seems to be refreshingly candid enough to admit a poor understanding of the subject due to scant and unreliable data.

The notes that Balfour compiled include one by Surgeon C. J. Smith (attested by Mark Cubbon of Cubbon Park fame). Smith notes that he has to rely on empirical wisdom due to the lack of reliable data and says: the superintendent of Coorg, in answer to a Circular from the Commissioner's Office, writes as follows: “They (the Coorgs) are fully impressed with the belief that to clear them (the jungles) extensively, would tend greatly to diminish the quantity of rain and of water in the rivers, and thereby destroy their paddy cultivation, the principal produce of Coorg, and also render the inhabitants less healthy,— thus it will be observed, that the general belief mentioned in the 3d para of the Honorable Court's despatch, extends itself to the Coorgs.” In another note Smith comments on the hills around Bangalore and states that the top of Nandi Hill was barren in 1849 unlike the adjoining hills (which today appear barren). The forest patch at the top of Nandi which includes some rather old Araucaurias and Eucalypts must then have been planted later.

Forest patch atop Nandydroog today
If this is so recent, the fact that this forest patch holds a small number of Nilgiri Wood Pigeon and a few other Western Ghats specialities must mean that they are recent colonizers.

In 1866 Clements Markham wrote an article "On the Effects of the Destruction of Forests in the Western Ghauts of India on the Water-Supply" in the Journal of the Royal Geographical Society of London (36:180-195).  The article includes an intricate map of the Western Ghats and the rivers arising from it. The following introduction could well have been written last week:
... many regions, in all parts of the world, which were once clothed with verdure are now treeless and arid wastes. All these changes are the work of man ; some took place centuries ago, others are going on now, under the eyes of this generation. The destruction of forests has been one of the chief agents in effecting changes in the earth's surface, and the best methods of counteracting evils which may be caused by these extensive clearances is one of the most important questions that occupy the attention of physical geographers.

This agency is now at work in the Western Ghauts of India, those rich and beautiful mountain-districts forming the backbone of the Indian peninsula, and containing the sources of a water supply, on which the prosperity - indeed, the very existence of millions depends.

Map by Edward Weller accompanying C R Markham's 1866 article.
Markham however believed that trees did not influence rainfall. "The forests which clothe their sides, and fill the valleys and ravines on their plateaux, hare the effect of regulating the flow of water to the eastward , but I cannot see that their presence or absence would have any influence on the actual amount of rain which falls on the hills. The intervention of mountains 8000 feet high, and the consequent change of temperature, will always wring the moisture out of clouds coming from the Indian ocean."
A Victorian alembic

Balfour (and Darwin) believed that montane plants condensed water. He called them "perfect alembics" (an alembic, derived from Arabic, is a distillation flask, here referring to the condensing end of it) with cupped leaves to drain water towards the stem and then to the roots. He even suggests that the bark is adapted for draining water towards the roots. None of this has been confirmed in later formal studies but during the months of December to March, many regions of the Ghats get a significant amount of mist and condensate and looking at the ground below trees, it is clear that there is far greater moisture gathered under them than on exposed ground or even grass. It does not appear as if anyone has attempted to quantify this water gathered but the usual practice of keeping rain gauges in a clearing ensures that this is excluded from traditional measurement of precipitation.
"In heavy fogs, in elevated situations especially, trees are perfect alembics, and no one, who has not attended to such matters, can imagine how much water one tree will distil in a night's time by condensing the vapour which trickles down the twigs and boughs so as to make the ground below quite in a float."
A recent book by Jonathan Adams (Vegetation-Climate Interation. How Plants Make the Global Environment. Springer. 2e. 2010 ) - includes several examples; a model that suggests that deforestation in the lowlands of the Appalachians caused peak rainfall to shift from the highland forests to the edge of crops and lowland forest; the city of Perth in Australia has had a 42% decline in river water flow associated with deforestation in the mid 20th century; and in Costa Rica, loss of lowland forest is thought to have made the clouds form higher above the montane forests, thus drying up the "cloud forest" zone.

On one trip to the Nandi Hills during summer, we noticed a substantial amount of water flowing down the trunks of the larger trees. The top of the hills tend to be covered in a cloudy mist at night and this seems to happen even to hills in rather arid places like Thiruvannamalai.

A millipede feeds on the bark as mist condenses and flows down the trunk (Nandi Hills)
It is really sad that most of the streams that arose from Nandi have gone dry. The horticulture department now plans to remove the trees on Nandi and put up an ornamental fountain to attract more visitors. On the Arkavathy valley below, roads cut across the stream path and the Hessarghatta lake along it has remained dry for years. Its bed is now being "developed" and where reeds grew, there are pits dug up to be planted up with avenue trees. Industrial houses dump effluents into the Vrishabhavathi river which finally drains into the Kaveri and then the city of Bangalore needs to pump water back from the Kaveri a 100 kms away and up nearly 900 metres to keep the people from going thirsty. This surely cannot go on for long.

Further reading

By coincidence, the Report of the 2011 Western Ghats Ecology Experts Panel is now up for comments. It is perhaps the last chance to save the Western Ghats from a minority few who in collaboration with a few politicians would like to destroy the region for their gain and everyone else's loss. Strangely the ministry does not have an open discussion forum on their site and instead seek comments via email to couple of ids.
In case you have comments that are publicly shareable and educational to others please feel free to copy your responses as responses to this post or email copies of your response to as many others as possible.