Every trip I take to a hilly area the smell of evergreens and floating mist reminds me of “Ruskin Bond” stories. The morning dew or afternoon showers in the driest season of the land, low hanging clouds entering homes and winds making an eerie sound in the forest of tall and dense evergreens. All these are the perfect setting for many of his stories loved by millions.
Forests and hills with low hanging clouds are always depicted together but people never really understood the significance. I had always thought that the formation of the vapour clouds, in non-rainy seasons were because of the trees. People always had one term” Local Precipitation” .
Fortunately someone else thought so and started to look at it scientifically. Rong Fu, a climate scientist at the University of California, Los Angeles. thought that plants were releasing enough moisture to build low-level clouds. She and her colleagues started studying the tropical forests of Amazon, using NASA’s Aura satellite, which shows the chemistry of Earth’s atmosphere. She could see clouds over the forest but to make sure that they were not drifted evaporated ocean water they checked the amount of heavier isotope of hydrogen in clouds .
When ocean water evaporates it leaves the heavier isotope in water due to different rates of evaporation but when trees transpire they give out water vapours having same isotopic composition as the water sucked in. Naturally the amount of heavier isotope in such clouds over forests would be more and it was observed to be so. This proved that trees make their own clouds. The higher the density of trees, the higher the probability of vapour clouds.
Due to more of deuterium oxide in transpired water, the vapor hangs quite close to the tress and drifts much slower than its lighter isotope. Also the freezing point being higher much more precipitation occurs.
These are the real ‘Rain Gods’.
What is true for Amazon is also true for the rest of the tropical forests, which we have been mercilessly cutting down in the name of development. That’s the reason these clouds are observed only in hilly forest covered regions in north and south India. Western and Eastern Ghats, Terai regions and foothills of Himalayas, and north-eastern hilly regions are few places left where one can find such dense forests in India.
Indus valley civilization to current droughts all have their origin in loss of green cover. We were taught till now that trees give us clean air and take up CO2. We never gave importance to this contribution of trees. When climate change is affecting seasons and monsoons trees are trying to maintain delicate ecological balance.
Scientific studies and satellite data remain mostly in academic circles and common people hardly get to know these important findings. Luckily this time on a trip to hill station somewhere in eastern Ghats of India I could actually see water vapour rising up from dense forest patch (still untouched) and going up to make the low clouds .(See the video here ).
An optical evidence to motivate people for not destroying forests. In the same region illegal rock quarrying have also started (photo).
I don’t think the green dense patch has long to live.