Desmatamento, clima e insegurança hídrica — parte 1: Rios voadores

The chief cause of drought is the unexpected change in rainfall patterns: rainfall was exceptionally low this year. The city of São Paulo, however, has faced other crises before: the worst drought occurred back in 1953 and and 1954. There was a similar occurrence in 1969, because the water supply systems weren't big enough.

The 1969 crisis was significant, in that it occasioned the construction of the Cantareira water supply system, which would supply water to the city of São Paulo until more or less 2015-2020. Subsequently, we knew we'd need additional systems. During this period, the Guarapiranga supply system was expanded, the Billings Reservoir was employed as an auxiliary supply system, and the Upper Tietê system was put into operation.

The Cantareira system was designed to supply water through a drought similar in magnitude to that of 1953-1954. We'd be in dire straits, but the systems were designed to see the city through this crisis. Nevertheless, as is the case with every natural system, the worst is yet to come.

The water levels in 2013-2014 are considerably lower than those of 1953-1954. The chief cause of the drought… Why didn't it rain? Not even meteorologists know why – variations in ocean temperature, a number of other things that don't fall within my field of expertise, and that I daren't try to explain.

But, from our point of view, which concerns the use of water, the fact is: it did not rain. If you look at the world map, you'll see that the Earth's deserts are aligned with the middle latitudes. There's the Namibian Kalahari in Africa, there's the Atacama over the Andes, there's the Australian Outback; in the northern hemisphere we have the Sahara, and the Sonoma in Mexico.

These deserts aren't aligned with the middle latitudes merely by chance. There's a type of atmospheric circulation called the Hadley cell: the winds rise in the equatorial regions because there's a bigger supply of energy there. And that's where they lose humidity.

That's why there's an abundance of forests in that region. The wind that rises advances towards the middle latitude and, where it descends, this dry wind "steals" humidity from the surface. So the region is naturally.

. . It shows a tendency towards aridity, unless it's very near the ocean.

Nevertheless, in South America, what we can call "the quadrilateral region" – Cuiabá to the north, Buenos Aires to the south, São Paulo to the east, and the Andes to the west – is geographically within the Hadley subsidence loop, so there's a lot of rainfall. So the mystery was: What's different about it? We have this enormous rainforest.

And what do we have there? A giant atmosphere irrigation system. What's so important about the Amazon?

How does the forest manipulate the climate? How can a region, which is 3. 000 km away from the ocean, be supplied with the ocean's humidity?

The ocean is the primordial source of all water. The wind carries this humidity into the continent and, as it moves further in, it produces rainfall, the air becomes drier. If there weren't some kind of mechanism with which to maintain the humidity in the air, the air, as it moved farther into the continent, would become completely dry.

What makes the Amazon rainforest different? The Amazon rainforest has trees. The larger trees in the rainforest have very deep roots that draw water from the phreatic zone – some 50 or 60 meters deep.

And their leaves are fantastic evaporation structures. A large tree, with a crown of 20 meters in diameter, a very leafy tree, produces up to 1000 liters of water in one day. When we take the entire Amazon rainforest into account, total production amounts to 20 billion tons of water per day.

To give you an idea of its magnitude: the Amazon River, which accounts for 20% of all the fresh water that reaches the oceans, all around the world, amounts to 17 billion tonnes per day. This atmospheric river which rises is much larger than the Amazon River. It becomes clear why this is so important to those who aren't in the Amazonian region and are supplied with its humidity.

The air contains a huge amount of vapor, even if it's saturated. If there isn't a particle If there isn't a particle to attract the vapor molecules in order to form liquid water, to form a cloud droplet – it won't be formed. The air over the Amazon forest is as clean of dust particles as the air over the ocean.

And the ocean is virtually a semi-desert, there's barely any rainfall. So the mystery was: What do we have in the Amazon rainforest? We now know that we have a source of humidity.

But what causes rainfall? The tree leaves have compounds that evaporate into the atmosphere. It was discovered that these vapors produce a reaction that precipitate in the form of dust.

And these particles, which we call atmospheric aerosols, are also known as cloud condensation nuclei. In other words, the Amazon rainforest produces its very own rain. We're used to thinking about evolution within life itself: plants reacting to plants, animals to insects etc.

What we're dealing with now is the evolution of life – the forest as a whole – as it interacts with the atmosphere. So, besides producing its own humidity, it also produces a phenomenon popularly known as "flying rivers", which explains why the quadrilateral region of Cuiabá, Buenos Aires, São Paulo, and the Andes is so green and humid – it accounts for 70% of South America's GDP. That's where all the hydroelectric power stations are located, the largest agricultural and industrial areas, the great centers… And the explanation was found in the flying river phenomenon – the Amazon rainforest "exports" vapor to this region and interferes with the region’s tendency towards desertification.

You've got this gigantic "ecosystem services plant", which is the forest – I call it the biggest technological park the Earth has ever seen. And what's being done to the Amazon? Our interaction with that "ecosystem services plant" is basically this: cutting it down with chainsaws and pulling it down with tractors, setting fire to it – we're transforming this "ecosystem services plant" into gas.

Regarding water supply, I think we won't get anywhere unless we deal with it in a multidisciplinary manner. The general behaviors shown by these systems are interlinked. But this drought is especially peculiar, because only two years ago we saw one of the highest water levels in the Cantareira system.

Deforestation didn't happen from one day to the next. Therefore, the rainfall patterns – and I'm talking about something that I don't really understand, which is meteorology –, but the rainfall patterns wouldn't have changed so abruptly. In 2010 and 2011, the reservoirs in the Cantareira system were full.

In my understanding of the subject, it isn't necessarily the change in the pattern of the flying rivers, but some other kind of variability. From the layman's point of view, the impression I get is that humidity hasn't stopped being produced in the Amazon – it just isn't reaching us. The regions that are beneficiaries of the Amazon's ecosystem services also had forests: the Atlantic Forest occupies an area of 1.

5 million square kilometers. The effect of losing this forest, which generated a friendly climate, wasn't strongly felt because the Amazon Rainforest – and I'm not making a direct connection, because I didn't study São Paulo, this is only an inference… And this inference is: if the best part of the humidity that reaches the regions in the South-Central region of South America came from the Amazon Rainforest, and the Amazon Rainforest, we know today, offers all these services – what's the logical conclusion? The logical conclusion is that we're killing the goose that laid the golden eggs.

Deforestation – that's an important subject because people sometimes say: "Oh, deforestation decreases the quantity of water". No. It only decreases the quantity of water during dry seasons, not the overall quantity of water.

When we have the forest, we see a decrease in maximum water flow, and an increase in minimum water flow, because part of what produces maximum water flow is "stuck" in soil ground and, later, when it stops raining, the soil will gradually release the water. When deforestation occurs, we see an increase in maximum water flow, because the rain runs and produces floods, and a decrease in minimum water flow, because the soil does not get saturated with water. But the overall amount is the same.

The water doesn't just disappear. The harmful effects of deforestation on the climate is irrefutable. But there are other effects, too: there's global warming, there are other regions around the world that are being negatively affected in the same way.

How much of it does global warming account for? Does global warming affect us even more negatively because we no longer have the Atlantic Forest here, nor the Amazon Rainforest there? I might conclude that this particular drought isn't related to Amazon deforestation.

But, in the next 50 years, if deforestation continues, I think it might be related, yes. So, for a long-term understanding, we really need a multidisciplinary effort. The things we know point us towards one direction: if the forest goes, we should should prepare ourselves for an inhospitable climate if you chop down a tree, you don't get its services; if deforestation continues and increases etc.

They've even got legal protection now, with the new Brazilian Forest Code, which conceded amnesty to those who practiced deforestation… There are verifiable alternatives like stopping deforestation and replanting forests. Reforestation not only of the Amazon. We know the forest plays a very important role in water supply.

And, so that people in São Paulo don't use the argument of: "Oh, that's not my problem. The problem lies within the Amazon and its deforestation" – it certainly is São Paulo's problem. Because there's an abundance of barren fields and hills all over São Paulo – which aren't used for agricultural or livestock purposes–, and there's no reason why they shouldn't be reforested.

But reforestation means – we spent 40 years destroying the Amazon and centuries destroying the Atlantic Forest because we used axes, not chainsaws – but it means that rebuilding will require patience. A tree takes decades to start producing all these effects. Nevertheless, we have to begin replanting.

I really hope that the crisis faced by São Paulo will serve as an example and a warning to people in other regions of Brazil. There are other possible sources that can supply São Paulo with water, but that gives rise to other problems: money and time. So the constructions that are being proposed are becoming increasingly more expensive because we have to draw water across increasingly greater distances.

That's why the demand management program is so important. But we'll consume less water and we'll have to pay for that investment. It'll be more expensive.

But I think that's more or less the path all environmental issues should take. People have to understand that if we want a more sustainable environment, it'll cost them – financially too. How probable is it that we'll go through a critical period of drought?

Only Saint Peter knows the answer to that. At any rate, in 2015, at least – if not 2016 –, it'll be tough. Even if we experience a so-called normal amount of rainfall in the summer, 2016 will still be pretty tough.

Personally, I'm very worried, because the month of October was a very dry month, and there should have been some rainfall, and the month of November has also been very dry. We're possibly heading to an extremely difficult year in 2015.