[P2P-F] Fwd: Rivers in the Sky: How Deforestation Is Affecting Global Water Cycles - Fred Pearce, Yale Environment 360

Fri Jul 27 16:22:01 CEST 2018

---------- Forwarded message ----------
From: Ryan Fortune <ryan.fortune2012 at gmail.com>
Date: Fri, Jul 27, 2018 at 12:30 PM
Subject: Rivers in the Sky: How Deforestation Is Affecting Global Water
Cycles - Fred Pearce, Yale Environment 360
To: michel at p2pfoundation.net

A growing body of evidence indicates that the continuing destruction of
tropical forests is disrupting the movement of water in the atmosphere...
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=7fb6170b1f&e=96e15d4563>

*Rivers in the Sky: How Deforestation Is Affecting Global Water Cycles*
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=907519f874&e=96e15d4563>

*A growing body of evidence indicates that the continuing destruction of
tropical forests is disrupting the movement of water in the atmosphere,
causing major shifts in precipitation that could lead to drought in
key agricultural areas in China, India, and the U.S. Midwest.*

*By Fred Pearce
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=4c2ca40bb3&e=96e15d4563>
Yale Environment 360
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=37c57ab7a3&e=96e15d4563>*
*24 July 2018*

Every tree in the forest is a fountain, sucking water out of the ground
through its roots and releasing water vapor into the atmosphere through
pores in its foliage.

In their billions, they create giant rivers of water in the air – rivers
that form clouds and create rainfall hundreds or even thousands of miles
away. But as we shave the planet of trees, we risk drying up these aerial
rivers and the lands that depend on them for rain.

A growing body of research suggests that this hitherto neglected impact of
deforestation could in many continental interiors dwarf the impacts of
global climate change.

It could dry up the Nile, hobble the Asian monsoon, and desiccate fields
from Argentina to the Midwestern United States.

Until recently, the nuggets of data delivering such warnings were
fragmented and often relegated to minor scientific journals.

But the growing concerns came to the fore in reports presented at two
forest forums held by the United Nations and the Norwegian government in
recent weeks.

In Norway, Michael Wolosin of the U.S. think tank Forest Climate Analytics
and Nancy Harris of the World Resources Institute published a study
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that
concluded that “tropical forest loss is having a larger impact on the
climate than has been commonly understood.”

They warned that large-scale deforestation in any of the three major
tropical forest zones of the world – Africa’s Congo basin, southeast Asia,
and especially the Amazon – could disrupt the water cycle sufficiently to “pose
a substantial risk to agriculture in key breadbaskets halfway round the
world in parts of the U.S., India, and China.”

*The water that a single tree transpires daily has a cooling effect
equivalent to two domestic air conditioners for a day.*

And in a background paper
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for
the UN event, David Ellison of the Swedish University of Agricultural
Sciences in Uppsala, reported on “increasingly sophisticated literature”
assessing “the potential impact of forest cover on water availability
across the broad expanse of continental, terrestrial surface.”

It is well known that carbon dioxide emissions from deforestation add 10
percent or so to global warming by reducing the quantity of CO2 that the
world’s forests pull from the atmosphere.

But the authors of both papers say this understanding about global impacts
of deforestation has tended to eclipse findings about other “non-carbon”
climatic impacts that may play out intensively at local and regional scales.

The impact of deforestation on rainfall is one of the most important
non-carbon effects. But there are others.

For instance, healthy forests release a range of volatile organic compounds
that “have an overall cooling effect on our climate,” mostly by blocking
incoming solar energy, says Dominick Spracklen of Leeds University in
England.

Removing forests eliminates this cooling effect and adds to warming, he and
an international team concluded in a study
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=676cbfd979&e=96e15d4563>
published
earlier this year.

Meanwhile, lost forests are usually replaced by agriculture, which produces
its own emissions.

Add in these impacts and the real contribution of deforestation to global
climate warming since 1850 is as much as 40 percent, conclude Wolosin and
Harris.

At that rate, tropical deforestation could add 1.5 degrees Celsius
(2.7°Fahrenheit) to global temperatures
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=eaf24c7ec7&e=96e15d4563>
by
2100 – even if we shut down fossil fuel emissions tomorrow, calculates
Natalie Mahowald of Cornell University.
------------------------------
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*On Indonesia's island of Sumatra, which has one of the worst deforestation
rates in the world, temperatures in logged areas have increased an average
1.05 degrees Celsius since 2000. AULIA ERLANGGA / CIFOR
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------------------------------

But there are local effects, too. Forests moderate local climate by keeping
their local environments cool. They do this partly by shading the land, but
also by releasing moisture from their leaves.

This process, called transpiration, requires energy, which is extracted
from the surrounding air, thus cooling it*.* A single tree can transpire
hundreds of liters of water in a day.

Each hundred liters has a cooling effect equivalent to two domestic air
conditioners for a day, calculates Ellison
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=ee1b8f135e&e=96e15d4563>
.

Monitoring of rapidly deforesting regions of the tropics has recently shown
the effect of losing this arboreal air conditioning.

Take the Indonesian island of Sumatra, which has been losing forests to
palm oil cultivation faster than almost anywhere else on the planet.

A study last year found that since 2000, surface temperatures there have on
average increased by 1.05 degrees Celsius (1.8°F), compared with 0.45
degrees in forested parts.

Clifton Sabajo at the University of Gottingen, Germany, found temperature
differences between forest and clear-cut land of up to 10 degrees Celsius
(18°F)
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in
parts of Sumatra.

Meanwhile in the Amazon, Michael Coe of the Woods Hole Research Center
recently reported a difference of 3 degrees Celsius (5.4°F)
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between
the cool of the forested Xingu indigenous park and surrounding croplands
and pastures.

*“The forests cause the rainfall, and if they weren’t there the interior of
these continental areas would be deserts,” says one expert.*

But heat is only the start. There is drought, too — not just in and around
former forest lands, but far away.

And a host of new studies are forcing a reassessment of exactly why it
rains where it does.

We are used to thinking of rainfall as the end result of water evaporating
from the oceans. In coastal regions that is overwhelmingly the case.

But it turns out that the interiors of continents often get most of their
precipitation from water that has been rained out and recycled back into
the air several times in a precipitation cascade following the winds.

The further inland, the more dominant this recycling becomes.

Some of the recycling is straightforward evaporation from lakes, rivers, or
wet soil. But much of it is fast-tracked by plants, and especially trees.

Tree roots tap moisture from deep in the soil. This circulation system is
driven by releases of moisture into the air through their leaves via
transpiration.

By one estimate, the planet’s land vegetation recycles 48 cubic miles of
water each day.

A tenth of that is released by
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=b69b716fe7&e=96e15d4563>
the
Amazon rainforest alone – rather more than the daily discharge of the
Amazon River.
------------------------------

*Trees pull water from the ground and release water vapor through their
leaves, generating atmospheric rivers of moisture.  - WORLD RESOURCES
INSTITUTE
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------------------------------

Transpiration is essential to generating new rainfall downwind. And the
heart of this process is in the surviving tropical rainforests, where
transpiration is most intense.

“Traditionally, people have said areas like the Congo and the Amazon have
high rainfall because they are located in parts of the world that
experience high precipitation,” says Doug Sheil
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=e9b1f828f2&e=96e15d4563>
of
the Norwegian University of Life Sciences, near Oslo.

“But the forests cause the rainfall, and if they weren’t there the interior
of these continental areas would be deserts.”

In a study
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=4a3bd23a91&e=96e15d4563>
of
tropical areas downwind of deforestation, Spracklen found that “air that
has passed over extensive vegetation in the preceding few days produces at
least twice as much rain as air that has passed over little vegetation.”

He predicts that forest loss is set to reduce dry-season rainfall across
the Amazon basin by 21 percent by 2050.

Arie Staal of Wageningen University in the Netherlands reported earlier
this year
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that
one-third of the rain falling in the Amazon basin comes from moisture
generated within the basin, mostly by transpiring trees.

The dependence was greatest downwind in the west of the basin, farther from
the Atlantic Ocean.

With a fifth of the Amazon forests gone, the risks of drought grow
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=a993e77c95&e=96e15d4563>
for
such regions. Coe reported less rainfall and a longer dry season
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=02afc6d73e&e=96e15d4563>
in
Rondônia, an Amazon province on Brazil’s western border with Bolivia.

*The Amazon provides moisture as far as the Midwestern U.S., which gets 50
percent of its rainfall from water evaporating from land.*

Daniel Ruiz of Columbia University says rainfall in the Colombian Andes is
becoming more seasonal, with reduced humidity and fewer clouds.
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Some
researchers believe the desiccation could stretch south to Argentina and
north across the Caribbean to North America.

The Amazon is thought to provide moisture as far as the Midwest, which gets
50 percent of its rainfall from water evaporating from the land.
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=19e64186ff&e=96e15d4563>

Attributing changes in rainfall to altered land use is difficult. But a
growing body of research asserts that the fingerprints of deforestation are
increasingly visible.

In Borneo, an analysis of nine watersheds
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=ac039c81f1&e=96e15d4563>
found
that those with the greatest forest loss have seen a reduction in rainfall
of around 15 percent. In India, Supantha Paul of the Indian Institute of
Technology in Mumbai found that patterns of declining rainfall during the
Indian monsoon matched changing forest cover.
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=119072084b&e=96e15d4563>

Patrick Keys of the Stockholm Resilience Center in Sweden says the downwind
effect of deforestation is not limited to the tropics.

“China receives a very large fraction of its rainfall from water that is
recycled from evaporation on land,” he told Yale Environment 360.

It “has very high potential for changes to its precipitation driven by
upwind land-use change” as far away as Eastern Europe and the jungles of
Southeast Asia.
This matters for farmers, but also for city dwellers.

In a study of 29 megacities around the world, Keys found that 19 relied on
evaporation and transpiration from land.

He singled out as the most vulnerable Karachi in Pakistan and China’s
Shanghai, Wuhan, and Chongqing.

Other cities such as Delhi and Kolkata in India, Istanbul, and Moscow were
not far behind.
------------------------------

*Forest mist in Pico da Neblina National Park, in the northern Brazilian
state of Amazonas.  PETER VAN DER SLEEN
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/
UNIVERSITY OF LEEDS*
------------------------------

In the Americas, he warned that the Brazilian megacities of Rio de Janeiro
and Sao Paulo and Argentina’s Buenos Aires could also be vulnerable because
much of their rainfall originates in the Mato Grosso region, where forests
and grassland are rapidly being replaced by corn and soy fields.

And what of Africa, the region of the world whose people are most dependent
on rain-fed agriculture? In Africa, drought can mean death.

But Keys estimates that up to 40 percent of sub-Saharan rainfall
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=6558d1c548&e=96e15d4563>
is
created by moisture that has been recycled by vegetation.

In the arid Sahel region, the figure may rise to 90 percent
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=cb3f4aee74&e=96e15d4563>,
says Louis Verchot of the Center for International Forestry Research
(CIFOR).

Recent research has highlighted the threat posed by deforestation to the
Nile River, the world’s longest river, and the 300 million people who
depend on it. Most of the Nile’s flow begins in the Ethiopian highlands, a
small rain-drenched part of the river’s catchment.

But recent research suggests that much of the rainfall in the Ethiopian
highlands comes courtesy of moisture recycled by the forests of West Africa
and, especially, the jungles of the Congo basin in the continent’s heart.

These rainforests “may provide as much as 30 to 40 percent of the total
annual rainfall in the Ethiopian highlands,” says Ellison.

Two questions arise. Has deforestation in West Africa been responsible for
the reduced Nile flows
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=8d331a845b&e=96e15d4563>
out
of Ethiopia seen in the final quarter of the 20th century, as suggested by
Ellison’s colleague
<https://twitter.us2.list-manage.com/track/click?u=00451369d2404e52ccee430a8&id=fb25f894c7&e=96e15d4563>,
Solomon Gebrehiwot, a researcher at Justus-Liebig University, Giessen in
Germany.

And could future loss of the Congo jungle empty the river further? Sheil
says Gebrehiwot’s data suggest a further 25 percent decline in Nile flow is
a realistic estimate.

Both Keys and Ellison see an urgent need for climate scientists and
diplomats alike to begin addressing these issues, so that pressure points
can be identified and policies adopted to protect rainfall in critical
places.

We have treaties governing river flows in most rivers that cross
international borders, they point out. But the rivers of moisture in the
atmosphere are rarely measured and never governed.
Egypt and Ethiopia have spent years working toward an agreement on managing
water flows in the Nile.

But a deal on sharing the water will be pointless if rains falter in the
Ethiopian highlands because of deforestation in the distant Congo basin.

In the current human-dominated era of the Anthropocene, says Keys,
“processes such as moisture recycling… can, and ought, to be governed.”
------------------------------

Fred Pearce is a freelance author and journalist based in the U.K. He is a
contributing writer for *Yale Environment 360* and is the author of
numerous books, including "The Land Grabbers, Earth Then and Now: Potent
Visual Evidence of Our Changing World," and "The Climate Files: The Battle
for the Truth About Global Warming."* More >>>
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