Scientists project a drier Amazon and wetter Indonesia in the future

Scientists project a drier Amazon and wetter Indonesia in the future
James Randerson, UCI’s Ralph J. and Carol M. Cicerone Chair in Earth System Science, said that worldwide shifts in precipitation – resulting in droughts in the Amazon basin and floods in Indonesia – start with tiny holes on the underside of leaves in the South American rainforest. Credit: Steve Zylius / UCI.

Climate models predict that an increase in greenhouse gases will dry out the Amazon rainforest in the future while causing wetter conditions in the woodlands of Africa and Indonesia. Researchers at the University of California, Irvine and other institutions have identified an unexpected but major factor in this worldwide precipitation shift: the direct response of the forests themselves to higher levels of carbon dioxide.

"People tend to think that most of the disruption will come from heat going into the oceans, which, in turn, will alter wind patterns," said James Randerson, UCI's Ralph J. & Carol M. Cicerone Chair in Earth System Science. "We have found that large-scale changes in rainfall can, in part, be attributed to the way tropical forests respond to the overabundance of humans are emitting into the atmosphere, particularly over dense forests in the Amazon and across Asia."

A new study led by former UCI postdoctoral scholar Gabriel Kooperman and published today in Nature Climate Change, demonstrates that interactions between rainforests and rising CO2 levels will contribute to an asymmetrical pattern of rainfall change across the tropics.

In many aspects of Earth system science, the local effects of environmental factors can impact faraway regions through their influence on the circulation and movement of moisture within the atmosphere. The UCI-led group predict a similar cascade of events, beginning with stomata, small structures on the underside of leaves that open and shut in order for plants to take in the CO2 they need to grow - and that also release water vapor.

When more CO2 is present, these orifices do not open as widely, which reduces the amount of water evaporated into the atmosphere. According to the researchers, this small process at the plant level, multiplied across the rainforest, will cause changes in the atmosphere, affecting the way winds blow and the flow of moisture coming from the ocean.

"In many tropical regions, the moisture supplied by transpiration, which connects water underground at the root level directly to the atmosphere as it is pulled up to the leaves, can contribute as much as moisture evaporated from the ocean that rains back down at a given location - which is normal rainforest recycling," said Kooperman, now an assistant professor of geography and atmospheric sciences at the University of Georgia.

"But with higher CO2, trees and forests evaporate less moisture into the air, so fewer clouds are formed above the Amazon," he said. "And rather than [joining with the usually abundant clouds and] raining over the forest, from the Atlantic Ocean blows across the South American continent to the Andes mountain range, where it comes down as rain on the mountain slopes, with limited benefit to the rainforest in the Amazon basin."

This recipe for drought in South America is unique to the Amazon and distinctly different from an increase in rainfall predicted over forests in Central Africa and the Maritime Continent, a vast area between the Pacific and Indian oceans that includes Malaysia, Papua New Guinea and the heavily populated Indonesian archipelago.

Randerson said that the reduction in evaporation will lead to warming over the forests on islands such as Borneo, Java and Sumatra, which are surrounded by humid air above warm ocean surfaces. "You'll get a stronger contrast in heating over the islands compared to the nearby ocean, and so it will enhance a natural ocean-land breeze, pulling in more moisture from these neighboring systems to increase rainfall over the forests," he said.

The research project, which used a combination of standard simulations provided through the Coupled Model Intercomparison Project Phase 5 and simulations with the state-of-the-art Community Earth System Model, revealed that the response of tropical vegetation to higher CO2 can be an important driver of climate change in the tropics, according to Kooperman.

He also highlighted the fact that the resulting droughts and forest mortality in the Amazon and a potential increase in flooding in other rainforests may have an impact on biodiversity, freshwater availability and food supplies for economically vulnerable populations.


Explore further

New study shows the Amazon makes its own rainy season

More information: Gabriel J. Kooperman et al. Forest response to rising CO2 drives zonally asymmetric rainfall change over tropical land, Nature Climate Change (2018). DOI: 10.1038/s41558-018-0144-7
Journal information: Nature Climate Change

Citation: Scientists project a drier Amazon and wetter Indonesia in the future (2018, April 27) retrieved 20 June 2019 from https://phys.org/news/2018-04-scientists-drier-amazon-wetter-indonesia.html
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Apr 27, 2018
Really, who cares what they project. They have no idea what is going to happen that far into the future. Witness the recent downgrade by 45% of the predicted global warming. So much for settled science. Really? They know it's going to be exactly 45% less now. Give us all a break.

The earth has cooled down like crazy in the past 2 years.

Just shut up about global warming. You are making yourselves look silly.

Apr 27, 2018
It sounds so much more sciencey if you say you plugged your educated and calculated guesses into a computer model; a model which represents a bunch of other guesses that haven't been actually validated. Because computers are never wrong. And the people who program the variables always get it right. Except for the massive fail of the CMIP5 models that even back in 2013 the IPCC Fifth Assessment Report noted (but glossed over).

https://www.ipcc....S-14.jpg

The models were tuned to replicate warming in the 80's and 90's but you can see that they all significantly over-project warming so with each passing year they diverge more from reality.

But that's to be expected when trying to model global climate. The problem is summed up nicely in IPCC AR5:

because the climate system is inherently nonlinear and chaotic, predictability of the climate system is inherently limited

Apr 29, 2018
Models are not science. Only one state has recorded any record high in the last 17 years. Better be worrying about how to grow food in a cooler climate.

Apr 29, 2018
Only one state has recorded any record high in the last 17 years
Wow - that's quiet a claim - maybe you could provide some support for it. https://www.yahoo...377.html

Bobsage - can we your support for the earth cooling in the last 2 years.....

Apr 29, 2018
Only one state has recorded any record high in the last 17 years
Wow - that's quiet a claim - maybe you could provide some support for it. https://www.yahoo...377.html

Bobsage - can we your support for the earth cooling in the last 2 years.....

What's your point idiot?

https://www.googl...in+years

Apr 29, 2018
I clicked report on you goracle - you have lost any debate, or any credibility when the first thing you default to is name calling.

Just for others on the board - goracle's support for the assertion that the EARTH has been cooling for the past 2 years - was a google search on the U.S. So how does it look to call someone asking a serious question - an 'idiot,' and then to show the world that you don't know the difference between one country - that is about 5% of the earths surface - and the entire earth?

Apr 29, 2018
I clicked report on you goracle - you have lost any debate, or any credibility when the first thing you default to is name calling.

Just for others on the board - goracle's support for the assertion that the EARTH has been cooling for the past 2 years - was a google search on the U.S. So how does it look to call someone asking a serious question - an 'idiot,' and then to show the world that you don't know the difference between one country - that is about 5% of the earths surface - and the entire earth?

Thanks for confirming what an idiot you are, Jackass.
The link in your post was for the US, so I provided you information for the US.....idiot.

Apr 29, 2018
The link in your post was for the US
There were two separate issues. b_man said
Only one state has recorded any record high in the last 17 years
So clearly b_man was making a claim about the U.S. I responded with my link - that was about the U.S. - as that was pertinent to b_man's comment. You notice there is no response from b_man.

Then I asked Bobsage for support about his claim that the EARTH is cooling. Again - notice no support for claims made by the denier community. It is clearly a pattern. Make stupid claims - hope no one notices - ignore any one who challenges you - move on to next article and make stupid claims. You responded to my asking Bobsage for support regarding the claim that the EARTH is cooling - with a google search about the U.S.

All we can say is that at least your inability to even reason at an elementary school level is on full display. Also how you have nothing substantive to say - so you name call.....

Apr 29, 2018
Earth's climate is changing. Just like it has, naturally for the last 500 million years.

Apr 30, 2018
Make stupid claims - hope no one notices

You keep braying like a Jackass Onion's. I noticed.

Apr 30, 2018
Thank you for your kind words goracle.

Asking for people who post rubbish - to actually support said rubbish - is not asking too much. Notice the crickets chirping.

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