Guest Post by Willis Eschenbach
For more than a decade now I’ve been saying something without getting much agreement, which was:
“When you cut down the trees, you cut down the clouds”.
I based my saying on my own experience, first growing up in a ponderosa pine and fir forest, and later living in a redwood forest for half of the last thirty years. My theory was that the trees created the rain in several ways.
First, they “transpire”, meaning that they release water into the atmosphere. And not just a little water. Lots.
Next, they absorb sunlight and use it to drive chemical processes through photosynthesis. This means that the sunlight is NOT turned into heat, which leaves the area cooler.
Next, they shade the ground, again cooling the surface and the local area. This allows the surface to stay moist, increasing the amount of water available for the plants to transpire.
Finally, some of the plants rake the fog out of the air, collecting it on their surface. From there it drops to the ground, watering the forest.
However, I’ve never had a scrap of evidence to support my theory that if you cut down the trees, you cut down the clouds. So I was very happy to find the following article in Science magazine:
Clouds over the Amazon.
Trees in the Amazon make their own rain
By Ilima LoomisAug. 4, 2017 , 2:45 PM
The Amazon rainforest is home to strange weather. One peculiarity is that rains begin 2 to 3 months before seasonal winds start to bring in moist air from the ocean. Now, researchers say they have finally figured out where this early moisture comes from: the trees themselves.
The study provides concrete data for something scientists had theorized for a long time, says Michael Keller, a forest ecologist and research scientist for the U.S. Forest Service based in Pasadena, California, who was not involved with the work. The evidence the team provides, he says, is “the smoking gun.”
Previous research showed early accumulation of moisture in the atmosphere over the Amazon, but scientists weren’t sure why. “All you can see is the water vapor, but you don’t know where it comes from,” says Rong Fu, a climate scientist at the University of California, Los Angeles. Satellite data showed that the increase coincided with a “greening” of the rainforest, or an increase in fresh leaves, leading researchers to suspect the moisture might be water vapor released during photosynthesis. In a process called transpiration, plants release water vapor from small pores on the underside of their leaves.
Fu thought it was possible that plants were releasing enough moisture to build low-level clouds over the Amazon. But she needed to explicitly connect the moisture to the tropical forest.
So Fu and her colleagues observed water vapor over the Amazon with NASA’s Aura satellite, a spacecraft dedicated to studying the chemistry of Earth’s atmosphere. Moisture that evaporates from the ocean tends to be lighter than water vapor released into the atmosphere by plants. That’s because during evaporation, water molecules containing deuterium, a heavy isotope of hydrogen made of one proton and one neutron, get left behind in the ocean. By contrast, in transpiration, plants simply suck water out of the soil and push it into the air without changing its isotopic composition.
Aura found that the early moisture accumulating over the rainforest was high in deuterium—“too high to be explained by water vapor from the ocean,” Fu says. What’s more, the deuterium content was highest at the end of the Amazon’s dry season, during the “greening” period when photosynthesis was strongest.
In looking around while writing this post, I also find this very interesting file from the National Academies, which says in part:
Certain trees are highly adapted to harvest fog water—some, like the Californian redwood trees, satisfy the majority of their water needs in this way. The trees create a physical barrier that intercepts and precipitates fog that would otherwise rise and dissipate in the warm air. In doing so, the trees create a localized water cycle: The fog water collected on leaves drips down and nourishes grasses, shrubs, and other plants that in turn trap their own water. All this dripping water sinks into the ground, filling wells and giving rise to small streams that people can use.
In addition, the redwoods provide the lovely sound of dripping rain, that marvelous music of watery wealth, even when there is no rain falling … what’s not to like? Here’s a photo I just took of the source of our liquid musical accompaniment, with my house in the foreground …
Finally, that same article that discusses the redwood trees is mostly about collecting water from fog nets. This is something I’ve discussed before in the context of the “no-regrets” option for responding to possible future climate change. See my post “Harvesting Fog: The No-Regrets Option” for one example.
My point was that IF someone wants to fight the eeevil CO2, they should do things that bring us value whether or not CO2 is the culprit. In that post, I said that if you are concerned for example about future droughts, do something now to fix the effects of present droughts. That way, you’ve taken a step that will help regardless of the future. It obeys the doctor’s maxim, “First, do no harm” …
Overall? It’s a lovely summer’s day, I’m back from the gold mines, we’re winning the climate battle, and life is good.
Best to each of you, sunshine and following winds …
w.
My Usual Request: Misunderstandings start easily and can last forever. I politely request that commenters QUOTE THE EXACT WORDS YOU DISAGREE WITH, so we can all understand your objection.
Here in SE Australia in the west of the state of Victoria, the Mallee scrub lands were cleared for agriculture back at the beginning of the 20th century.
Some large areas of scrub land ie “Big Desert” of some 1500 sq kilometres, the Sunset Country of NW Victoria and the Little Desert were left as the soils under those scrublands were too poor for even those early pioneers to clear and farm.
Those farmers living and farming along the cleared farmlands that butt up against the edges of the Desert vegetation are quite adamant that there is a substantial rain fall drop off when they go more than a few hundred metres away from the desert vegatioin edge into the cleared farmlands.
A couple have told me that in some places on their farms nearest the Desert edge they can quite literally walk along the leading edges of showers of rain coming out of the Desert and not get wet as the shower just stops abruptly at a very close and constant edge / line a few tens of metres out side of the desert vegetation edges and into the hundred year old cleared farm land.
The effect is probably particularly strong in Australia since Eucalypts are essentially natural CCN (Cloud Condensation Nuclei) makers.
Rain-making cloud seeding experiments of the 20th century were just trying to mimic nature. But usually with the wrong CCN.
I saw an example of the same process reducing available water in central Montana. In surveying most of a township (36 sq. mi) I used original notes from the late 1800s that noted water courses and timbered areas. I also visited with all the old timers I could find to discus their memories of boundary markers. About 4 years before my survey a large fire burned several thousand acres in the area. When I got there the streams mentioned in the old notes were active with new growth starting along them. The old timers said they had never seen water in most of the stream beds except in the spring. My theory is the pines matured throughout the early 1900s and eventually transpired most of the ground water. When the fires killed them there was enough to get to the surface again. The area was high rolling semi-arid (about 12 in./yr) mostly plains with patches of timber.
Similar phenomenon in South West Australia apparently: http://joannenova.com.au/2013/12/land-clearing-responsible-for-most-of-rainfall-decline-in-south-west-western-australia/
Hi Willis: I expected your article to be at least in part based on your experience with islands in the South Pacific. This is only anecdotal, but the island of Kahoolawe, just off Maui in the Hawaiian islands and readily seen from my Maui home, was at one time covered with trees. But WWII occured and the island was used as a practice bombing range until the 1980s, completely denuding it. Bombing no longer occurs, but the island now gets very little, if any, of the daily island, tropical rains. But I listened to a talk from a person who lived on Maui, across from the readily seen Kahoolawe prior to WWII. She said the island used to be covered with trees, and clouds formed regularly over Kahoolawe with resulting rain, and she lamented that since the trees were destroyed such rain clouds no longer form. And it is true that rain clouds now seldom form over Kahoolowe. Additionally, the inhabitants of the neighboring Island of Lanai also attribute some of their rain to the trees covering the top of that island. Again, sorry, only anecdotal. Both Kahoolawe and Lanai are otherwise below the normal 4,000 foot cloud ceiling at this location.
Fascinating. I lived for about six months on Makena Beach on Maui in 1972 or so, and I recall Kahoolwe invariably being parched. Never heard your story, but it makes perfect sense.
w.
Do trees make it rain?
Yes.
http://dewharvest.blogspot.com/2014/05/do-trees-make-it-rain.html
My experience in the Galapagos Islands, as everywhere else I’ve been, lived and worked, say yes, as well.
In the Galapagos, there is essentially no topsoil. The “trees” are giant dandelions. But islands of the right geological age to sport such forests enjoy sufficient rainfall to support large animals. Those too young or too old, don’t.
Rain follows the trees, not the plough.
“Next, they absorb sunlight and use it to drive chemical processes through photosynthesis. This means that the sunlight is NOT turned into heat, which leaves the area cooler.”
If true, this would be a powerful negative feedback on rising temperatures from CO2, since that added CO2 would stimulate plant growth and diminish the amount of radiative energy used to warm the surface that would have been exposed but for the new plant growth,
The idiotic, ignorant assumption of “climate science” charlatans and morons is that net feedbacks are positive. This is almost never the case on our homeostatic planet. Net feedbacks from more CO2 are almost certainly negative on this self-regulating world.
Hence, the lab value of 1.2 degrees C temperature increase per doubling of CO2 is almost certainly less than that after net feedback effects. Possibly if not probably net cooling.
The Greening of Ascension Island
Two hundred years ago, Ascension Island was a barren volcanic island. Today, its peaks are covered by a lush tropical forest.
Thanks to the experiment of Charles Darwin and his buddy Joseph Hooker. If it weren’t for the plantations of trees from Kew Gardens, the present population and permanent military base would be unsustainable because of the lack of water.
Hiring young Cambridge divinity grad Charles Darwin to accompany CPT Robert Fitzroy on HMS Beagle was the best money ever spent by the Royal Navy, since it cost the sea service nothing but led to the greatest advancement of science in the first half of the 19th century.
Absolutely
An overview of that story can be found f.x. here:
http://www.bbc.com/news/science-environment-11137903
I.e. the story of Darwin’s “terraforming” experiment on Ascecsion Island.
Thank you Willis.
A very entertaining and informative post, as always.
I agree, it’s a very interesting post with lots of good comments.
CERN in Switzerland, through their CLOUD experiment, has shown that biogenic vapours emitted by trees and oxidised in the atmosphere have a significant impact on the formation of clouds, thus helping to cool the planet. These biogenic aerosols are what give forests seen from afar their characteristic blue haze. The CLOUD study shows that the oxidised biogenic vapours bind with sulphuric acid to form embryonic particles which can then grow to become the seeds on which cloud droplets can form. This result follows previous measurements from CLOUD showing that sulphuric acid alone could not form new particles in the atmosphere as had been previously assumed.
Link http://home.cern/about/updates/2014/05/cern-experiment-sheds-new-light-cloud-formation
Abstract: http://science.sciencemag.org/content/344/6185/717
I was going to chime in pointing out terpene chemistry is important in cloud condensation nucleii formation. I have observed in Oz there is a very strong smell of Eucalptus oil after rainfall breaks a dry spell. Hard to say if that is because the trees emit more VOCs after rain, or rain washes out the oxidants that remove VOCs. I always thought it would be an interesting area of study, not without its challenges, but important given it could be a climate feedback, and therefore play a role in explaining rainfall pattern changes over the last 500 years of extensive deforestation. Silly me, its all due to dirty coal though isnt it.
You’re not the first to observe this effect Willis. In 1776 the Main Ridge forest reserve on Tobago was created:
“for the purpose of attracting frequent showers of rain upon which the fertility of lands in these climates doth entirely depend.”
And in 1791 the Kings Hill Enclosure act was put into effect on St Vincent “to preserve the trees growing thereon in order to attract clouds and rain”.
As far as I know those were the two first forest reserves in the Western Hemisphere (a centurey before Yellowstone). At least the Main Ridge reserve is still in effect (been there).
And I have been told by locals in Guatemala that logging of the mountain forests there decreases the amount of rain.
Trees make more of what they like. Rain. The produce both the moisture and the nucleus to form upon to enable more forrest thereby making the habitat they like spreading themselves.
few years ago I was in the rice terraces in Southern China and was talking with a local about the water supply to the terraces – streams from higher up in the hills. He said that in the Mao era, they were forced to cut all of the trees on the upper slopes to provide charcoal for local iron-making furnaces. As a result, the streams stopped and rice crops failed as a result. They have since reforested the area and bingo, the stream flow recovered. Much reforestation happening in China, for the combination of water supply, slope stability and wood supply – they plant in terrain rows and harvest the same way, with rows of usually 3 ages.
I expect there is a lot on forests and water supply in Chinese academic literature.
This is a really great discussion and I want to raise a possible explanation for why N.Africa became a huge desert in the last ten thousand years. Since we know that what is now largely the Sahara desert was a rich grassland with water inhabited by rich game and people, it would seem reasonable to follow on with the reason for desertification being a fall in global CO2 levels leading to tree loss rather than people chopping trees down or drying up from wind pattern changes. Actually if the distance in time back to the end of the last ice age is greater than the age of the Sahara desert, CO2 depletion is a better explanation since globally there was more moisture in the air.
The Egyptians may well have circumnavigated Africa according to one text of one of their voyages.
But I love the image of Coke snorting pharaoh, unfortunately the mummies don’t seem to have eroded septums. Maybe they just mixed it in evening cocktails.
My thoughts are that it’s more to do with animal husbandry. I blame mostly reduction in trees in a marginal place, goats are by far the worst offenders of human livestock. They make deserts of near anything. Many islands in the Mediterranean Sea have also lost all their trees and behold become mostly deserts. The updrafts of humidity break up the air and make thundershowers. A good study would be to remove the goats and replant a few islands and see what happens.
Mydrrin August 9, 2017 at 8:58 am
When I lived in Africa, I used to say that Africa would soon be a paradise if every day, every African killed one goat and planted one tree … people thought I was kidding.
w.
Once upon a time i saw the following explanation (hypothesis) for the desertification of Sahara:
Sometime between 11 an 13 thousand year ago some event (possibly a big asteroid collision ) the caused significant change in the orbit around and the mean distance of the moon from the Earth. This in turn lead to at change in the declination of the Earth’s rotational axis big enough to change the the hydrology of Africa and turn a previously lush green area into a desert within a couple of millennia. Do not remember on what the basis of data and facts for this was , but i remember it looked to me it might very possible the hypothesis was correct on the face of it.
Nature wonders, humans wander. Go green, plant a tree.
It would seem unnecessary to use such sophisticated methods to prove that the clouds/rain in the Amazon is mostly recirculated locally. The Amazon basin is unique in the world in having a very wet climate deep in the center of a continent. Ultimately the water comes from the ocean and returns there but it quite obviously is recycled several times on the way.
The Amazon basin is unique in several ways. Originally it opened to the west and became wider in that direction as river basins mostly do. Then the Andes rose and blocked the original mouth and created a vast inland sea draining through a narrow gap to the east. This sea silted up and turned into a huge swampy dead-flat plain. Now the Amazon collects rain falling in the surrounding highlands all the way from the Caribbean to Mato Grosso which slowly meanders across that plain and finally makes it way to the Atlantic. But it has evaporated and rained back several times on the way.
One only has to look at a satellite image like this (from EUMETSAT) to see how it works:
https://www.smhi.se/vadret/nederbord-molnighet/satellit-jorden
Just “drag” the time on the right and watch how the thunderstorms build up during the day and rain out and collapse during the night. Every day, all the year, though the center shifts from the northern part of the basin in summer to the southern part in winter.
By the way EUMETSAT happens to be located over the only other area on Earth with a somewhat similar geography and climate, but on a much smaller scale, i. e. the Congo basin.
Funny. I had a college professor that simply stated as fact that trees make clouds (about 15 years ago).
Next, they’ll realize that the millions are acres of corn in the Midwest cause thunderstorms.
Either way, the total volume of water vapor isn’t the only factor. Many plants release cloud condensation nuclei.
When we look at ocean iron fertilization (growing forests in the ocean) they make more clouds, too. Phytoplankton release cloud condensation nuclei.
In theory, the perfect ocean iron fertilization program could have a huge return on investment. They restore fish populations, can make clouds to reduce droughts, and transport some amount of CO2 from the atmosphere to the bottom of the ocean.
Photosynthesis does consume energy, however, from what I have read photosynthesis is only about 2 to 3% efficient.
The color of the leaf compared to the color of the ground it is shading will have a much greater impact. If the leaf is darker than the ground, then the lower albedo will have a much greater impact than the tiny amount of energy converted by photosynthesis.
Mark,
Photosynthesis uses about 115 kilocalories per mole of co2.
http://www.fao.org/docrep/w7241e/w7241e05.htm#1.2.1%20photosynthetic%20efficiency
Also more than a decade ago:
Anastassia Makarieva and V. G. Gorshkov, 2006
Biotic pump of atmospheric moisture as
driver of the hydrological cycle on land
Willis,
The study of trees and evaporation has a long history in hydrology and this question is of great interest to water engineers. For example in this 1979 paper:-
Calder, I.R. and Newson, M.D., 1979. LAND‐USE AND UPLAND WATER RESOURCES IN BRITAIN‐A STRATEGIC LOOK. JAWRA Journal of the American Water Resources Association, 15(6), pp.1628-1639.
In the 1970s I and my fellow undergraduates visited the experimental forest lysimeter in the Stocks Reservoir catchment in the Forest of Bowland, Lancashire. Here we saw the first such experimental work in a representative British upland area devised by the late Frank Law, Engineer to the Fylde Water Board, which showed that the plantation fir trees “used” more water than the sedge sheep pasture of the hill farms on the surrounding fells.
I cannot now be exactly certain of the tree species in the lysimeter, but I think that they were they were spruce (either Norway or Sitka). The explanation given to us for the fact that the land under the tree canopy produced less runoff into the reservoir was that the trees intercepted the rain and the water re-evaporated directly from the dense needles, rather than increased evapotranspiration. I later remembered this result, with its confirmation of the simple experience of any upland hill walker in the British Isles that if you want shelter from the rain then a dense spruce plantation is a good bet, when I saw the effect that a group of Wych Elms had on a sea mist on the east coast of England. In contrast with the dry floor of the spruce plantation on the Bowland Fells, the hairy twigs of the elms were literally stripping the moisture out of the mist so quickly that the water dripped to the ground almost as if it was raining.
So the direct physical presence of the trees changes the moisture interaction of the air and the ground in different ways depending on the species and the climate circumstances. Dense needle firs can intercept the falling rain, return the water to the low level air and reduce soil moisture below the canopy, whereas other species, like the Wych Elm, can directly harvest moisture from a fog and so increase the water in the ground below the trees, as is observed in cloud forests.
Climate models are silent on this.
I’m with you Willis. I can’t believe you didn’t reference “The Man Who Planted Trees” to set the mood for your essay. GK
https://youtu.be/aY_zuNtf3_g
On a wooded hill, the trees will slow the wind somewhat and thus increase the chance of rain or condensation. The cooler area in the shade below the trees might help. I wouldn’t know the name of such phenomena, absolutely not my area.
So your saying we shouldn’t cut down forests for biofuel crops?
I dunno how to begin calculating, but one would imagine that this can impact local/regional temperatures.
Let’s look after the forests. Its just a smart thing to do.
This seems to be related:
“A small belt of two to three metre high saxaul trees (Haloxylon persicum) found inland to the south of Abu Dhabi has been dubbed the ‘dew forest’ on account of its foliage dripping condensation. The plant essentially waters itself, as any dew that so forms will drip onto the ground around the plant before it evaporates. This fog moisture is clearly of great importance to the saxaul because it has a highly restricted distribution locally, covering an area of something under 2000 square kilometres (less than 1 per cent of the total area of the UAE). ”
So if you do visit the UAE, go out into the desert early in the morning, and marvel at the Abu Dhabi dew.
On Tenerife they use the condensation effect of pine trees for their water supply.
https://tenerifeexplored.blogspot.de/2009/12/tenerife-water-supply-where-does-from.html
The pines ‘produce’ much more water from fog than they need for themselves. This is a somewhat opposite effect as described here.
Very informative article. I have a slightly different perspective on some aspects:
“Next, [trees] shade the ground, again cooling the surface and the local area. This allows the surface to stay moist, increasing the amount of water available for the plants to transpire.”
Does it make any difference if SWR is absorbed by trees or the ground below? Both transfer the energy they absorb (except for photosynthesis) into heat which they radiate, convect or conduct to the atmosphere. Some surfaces – like sand on a beach on a sunny day – can get much hotter than trees do and therefore radiate away more heat. Trees obviously have more surface area for conduction.
Corn is supposed to be one of the most efficient plants are converting absorbed photons into chemical energy. It is about 1% efficient. So the other 99% of absorbed SWR becomes thermal energy.
However, trees can reflect more SWR (which we perceive as their green color) than the ground. This cooling effect depends on the albedo of the ground beneath the trees.
Once water has soaked into the ground, it is very hard for it to reach the surface again to evaporate. Tree roots take up ground water and move to leaves where it can evaporate. In the Amazon, tree roots reach 10 m below the surface into the water table.
The roots from even grasses bring water up from a foot below the surface. Ancedotal sources suggest that the AOGCMs find two stable states for the Sahara desert: today’s desert or grasslands that return precipitation to the atmosphere as water vapor that can fall again rather than sink underground. As you probably know, about 5,000 years ago, the Sahara was green.