How Forests Create Rain: a New Study on the Effect of Evapotranspiration

From the "Proud Holobionts" blog

Image created by Dall-E

The idea that forests create rain has been known by peasants for hundreds, perhaps thousands, of years. The first scientific studies go back to Alexander von Humboldt (1769–1859), but the subject remains controversial. Nevertheless, we are starting to understand the deep and complex interactions between the atmosphere and the biosphere. They form a true "holobiont," a system of connected elements that affect each other in non-linear ways. A recent paper published by a research group led by Anastassia Makarieva shows how evapotranspiration, the evaporation of water by trees, modifies the water vapor dynamics and may generate high moisture content regimes that provide the rain needed by the land ecosystem. There is still much that we need to understand about these mechanisms, but one point is clear: forests are a crucial element of the stability of Earth's climate, and they must be preserved as much as possible (U.B.)

Press Release, 14/03/2023

As water scarcity globally grows, and deforestation threatens the remaining natural forests, understanding how vegetation impacts the water cycle becomes increasingly important.  In their new paper, “The role of ecosystem transpiration in creating alternate moisture regimes by influencing atmospheric moisture convergence” published in Global Change Biology ( https://doi.org/10.1111/gcb.16644), an international and interdisciplinary team led by TUM demonstrated the existence of two potential moisture regimes – one drier, with additional moisture decreasing atmospheric moisture import, and one wetter, with additional moisture enhancing atmospheric moisture import. In the drier regime, water vapor behaves as a passive tracer following the air flow. In the wetter regime, it modifies atmospheric dynamics.

The team based their analysis on the previously established non-linear dependence of precipitation on atmospheric moisture content – increasing absolute humidity leads to a negligible precipitation increment if the atmosphere is dry, but to a large increment when the atmosphere is sufficiently wet. Combining this dependence with a full consideration of the water budget, the researchers showed that an increase in precipitation in humid conditions facilitated by increased evapotranspiration, should lead to enhanced moisture import. They illustrated these patterns with the data from the Amazon basin and the Loess Plateau in China.

Dr. Anja Rammig (TUM School of Life Sciences and study author) considers these results as having profound implications for the ongoing studies of the resilience of the Amazon forest in the face of the danger of deforestation and climate change. Dr. Scott Saleska (University of Arizona, study author) believes that the new results are in agreement with the profound role of leaf phenology in the Amazon forest for water cycle regulation. By forcing a decline in forest evapotranspiration, deforestation can dehumidify the atmosphere and thus drive the forest into the drier regime where transpiration of the re-growing vegetation would further aggravate aridity by decreasing moisture import. Getting out of this landscape trap could be impossible. Dr. Ruben Molina (University of Antioquia, Colombia, study author) hopes that the study findings will raise the awareness of the importance of tropical forest conservation.

Dr. Andrei Nefiodov (Petersburg Nuclear Physics Institute, Russia) participating in the study says that the new results corroborate the concept of the biotic pump of atmospheric moisture that emphasizes the dominant role of natural forests in transporting moisture inland. Dr. Antonio Nobre (INPE, Brazil, study author) compares this biotic moisture pumping to a beating heart, and highlights the good news: even in arid lands, by restoring the vegetation one should be able to enhance the atmospheric moisture convergence and streamflow. To achieve that, the ecological restoration strategy should be carefully designed to guide the ecosystem transition from the dry to wet regimes.

“I suspect that natural vegetation will be best for maintaining a moist and productive environment as these systems kept the world green and productive long before people got involved” – emphasizes Dr. Douglas Sheil (Wageningen University, author), collaborating on the research. “We do need to take into account the holobiontic relationships among all ecosystem elements that allow for an efficient regulation of the water cycle,” adds another author Dr. Ugo Bardi (Club of Rome, University of Florence).

Anastassia Makarieva (Institute for Advanced Study, TUM, lead author) emphasizes the need for a broad international cooperation in the studies of the ecology of the water cycle: “We have shown that the non-linear precipitation dependence on atmospheric moisture content, first noted by our co-author Dr. Mara Baudena (CNR-ISAC, Italy) and her colleagues, has widely ranging implications. The atmospheric water flows do not recognize international borders, thus deforestation disrupting evapotranspiration in one region could trigger a transition to the drier regime in another. Our results indicate that natural forests of the Earth, in both high and low latitudes, are our common legacy of pivotal global importance as they support the terrestrial water cycle. Their preservation should become a widely recognized priority for our civilization to solve the global water crisis.”

Makarieva, A. M.,  Nefiodov, A. V.,  Nobre, A. D.,  Baudena, M.,  Bardi, U.,  Sheil, D.,  Saleska, S. R.,  Molina, R. D., &  Rammig, A. (2023).  The role of ecosystem transpiration in creating alternate moisture regimes by influencing atmospheric moisture convergence. Global Change Biology,  00,  1– 21. https://doi.org/10.1111/gcb.16644

Science, Forests, Bears, and Clouds

 From "Kelebek," Miguel Martinez's blog

12/12/2021

by Miguel Martinez

Last night at sunset, a big chill, dark red clouds to the west. And the half moon, above the black cypress trees to the right, silhouetted against the fire of the dying sun.

Below  Bellosguardo, that silent little wall where sometimes a black cat walks, and to the left you can see the snow on the mountains, and, below, the city of the old enemy, Fiesole....

We go up towards Marignolle, and Marco recites to me the verses of the mad poet, Dino Campana:

To the ghostly garden of mute laurels

To the green garlands

To the autumnal earth

A final greeting!

Walking between the silent walls that hide the secrets of an occult city, we arrive at the villa of the ancient family.

From one end of the great hall, Abraham looks at us in an eighteenth-century painting, as he prepares to sacrifice Isaac; from the other end, the ancestor of the family looks at us in a portrait, and has the same beard and the same look (and faith) as Abraham. And between the two, the menorah, on the wooden sideboard that bears the date MDCXXXVII engraved on it.

We gathered to hear Anastasija Makarieva, black hair, almond-shaped blue eyes and high cheekbones, from the Institute of Nuclear Physics in St. Petersburg. An institution heir to that other half of the world, which not only managed to build Soviet atomic bombs from scratch, but explored worlds unknown to Westerners.

Anastasija (with the accent on the "i") doesn't deal with atomic bombs at all, but with forests.

We've all heard of the forests of the Amazon, but we never talk about the perhaps even larger ones that stretch from the Baltic to the Pacific.

Now, as an oriental language major who has a hard time telling an ash tree from an elm, who hasn't taken notes, and is going from memory, I'm going to try to report to you what Anastasiya said, any nonsense is just my own.

It is said that we are living an immense environmental crisis, linked to CO2 emissions with related global warming; and that we must therefore reduce these emissions.

Which however has a huge consequence: if the problem is too much CO2, we reduce CO2 even at the cost of an extermination, end of the problem. The war against climate change is all there.

The scientists in St. Petersburg do not deny the issue of emissions at all, but they say that there is another factor, which is perhaps even more important, that is leading us towards climate catastrophe.

If life exists, it exists because the biosphere exists; and the biosphere is intimately linked to something the Russians call the biotic pump.

Trees are apparently remarkably incompetent machines: they disperse 90% (I'm quoting from memory) of the water they absorb into the atmosphere.

But coastal trees catch what little water the sea sends down to the earth; they alone, through evapotranspiration, are able to make what by its nature goes down go up. Emitting not only water, but also other substances that allow the water to condense, they form clouds, and through various very complex mechanisms - which complement those known to meteorology - they create winds, which bring moisture inland.

And they therefore allow life on the continents, and generate rivers. So, life on earth depends on the forest world. But it's not enough to plant millions of trees at random, as the technogreens would like to do.

Anastasija tells us about the fir trees, planted en masse at the beginning of the twentieth century, in Bohemia, which today have been infested and destroyed in a short time by pests, because there is no variety; about the problem of coeval trees - the biotic pump really works only when there is the set of trees of many generations, with the whole surrounding ecosystem.

And an American artist listening to us tells of a friend of his, who in order to recreate a forest, very slowly took the humus of a still intact forest, with all its variety.

Siberia and Amazonia are the two forest poles of the world, in their immense diversity. But for some reason, the Siberia they're selling off to the multinational timber industry doesn't seem to interest anyone.

"I've only been to Siberia twice," Anastasija admits. "But every year my partner and I camp in a tent on the coast of the White Sea."

Once we saw a bear. From very far away... so we got closer.

We found him in front of us, and then I felt inside me, what the bear was thinking inside his head: the end had come!

He looked one last time at the sea, then turned around, trying to show as little as he could of his profile. And then suddenly, he gathered all his strength, and ran off into the woods!"

And she gives us the picture of the owl, seen in a tree far, far north, with which we open this story.

Anastassia Makarieva in Florence: Explaining how the Biotic Pump Works

Republished from "The Proud Holobionts."

Anastassia Makarieva  (center) receives a gift of appreciation for her talk in Florence, on Dec 11th, 2021, from Nicola and Anna in the form of a jewel made by Nicola, jeweler in Florence.

From "The Proud Holobionts," by Ugo Bardi

This week, we had the pleasure of a visit to Florence of Anastassia Makarieva, one of the world's most creative and brilliant scientists in the field of ecosystems. Anastassia is the originator, together with Viktor Gorshkov, of the concepts of "biotic regulation" and "biotic pump" -- both fundamental in our understanding of the functioning of the ecosphere. Together, they mean that the current climate change is only in part the direct consequence of the increase in greenhouse gas emissions, but in significant part the result of the human perturbation of the ecosystem, and in particular the destruction of the old-growth forests. 

So, Anastassia bears a message: it is vital for the planet to keep forests alive and in their pristine state. And that means just what the word says: forests, not just trees. Those politicians who compete for who plants more trees are just doing greenwashing. They may be harming the planetary ecosystem more than helping it. A tree, alone or as part of a plantation, does not have the same balancing effect and water carrying system that a forest has. A message that's not easy to understand for the current generation of decision-makers, used to the concept that a tree is worth only what profit it can provide once it is cut and sold on the market. Nevertheless, we must try to pass this message. 

For Anastassia's talk in Florence, we experimented with a new format of presentation. The university, nowadays, has become something like Dracula's castle, with the difference that it is a scary place even in the daytime. To have Anastassia give an "official" talk, I should have gone through I don't even know what mass of paperwork, and then her talk would have been attended only by the few academics who still have some interest in creative research. All that in a super-safe, soulless room. 

To say that these official seminars can be disappointing is an understatement. A few years ago I organized a talk by a Russian scientist on the question of the supply of gas from Russia to Europe. You would think it is an interesting subject in Europe. Well, the attendees were exactly zero, besides me, the sponsor of the talk, and the Russian scientist herself. And at that time there was no Covid yet to make people afraid even of their shadows.   

So, this time we decided to play it differently: a colleague of mine kindly offered her living room to host Anastassia's seminar and we announced it on the social channels in addition to the regular university channels. We also offered drinks and snacks. We didn't know what to expect and we had no idea of how many people would bother taking a trip to the hills near Florence to listen to a Russian researcher speaking in English about her research. 

It was a remarkable success. Not a big crowd, but we collected about 25 persons, of whom only 3 were professional scientists (I think they were those who would have shown up had we organized the talk in the university). And they all listened with extreme interest to Anastassia's talk, fascinated by the story of how the ecosphere stabilizes climate and how the forest's biotic pump creates wind and rain. When it was the time of telling the story of how Anastassia and Viktor survived for months in the Boreal forests in a tent, with bears strolling nearby, the audience was completely captivated. The informal party after the seminar was an occasion to build up friendship among people who share the same views of the world, even though they are not necessarily scientists.  

There is something to learn, here. Science is not a Moloch to worship, nor a dictator to be obeyed. And it is not even a conventicle of hyperspecialists who know so much about so little that they can be said to know everything about nothing. Science is one of the several possible embodiments of the concept of "philosophy," the love of knowledge. It is something that does not belong to anybody, it belongs to everybody. And that was clear at Anastassia's talk. 

h/t Benedetta Treves and all those who helped organize this seminar. To know more about the biotic pump and biotic regulation, see the site https://bioticregulation.ru/