November 15, 2013
Barren Amazon May Cause Drier Winters On US West Coast
What would happen if the Amazon basin – home to the world’s largest rainforest – was completely stripped of its trees, through human activity as well as global warming?
Rainfall in South America would reduce dramatically, farmlands would shrink and hundreds of animal species would simply disappear.
But new research shows that complete deforestation of the Amazon could also have an effect on the weather several thousand miles away near the west coast of the United States.
A study published in the Journal of Climate predicts that a barren Amazon will give rise to abnormally dry weather patterns in winter that could be carried up towards the US West Coast.
As a result, winters in states like California would become drier, with the snow cover on the Sierra Nevada mountain range reducing by half and rainfall along the coast dropping by 20 percent. This would affect not only agriculture in California’s Central Valley but also the region’s freshwater supply.
Such dry winters could have “serious consequences” for food supply in the US, said David Medvigy, assistant professor of geosciences at Princeton University and study lead author, in a release.
Scientists have earlier predicted that deforestation in the Amazon could disrupt surrounding weather patterns by bringing dry air to already-arid regions and rainfall to already-wet regions − similar to the El Niño temperature patterns of the Pacific.
El Niño refers to the quirky southern weather patterns that abruptly change ocean temperatures and bring unexpected − and often destructive − rainfall to the west coast of South America, while drying out the east.
It is not just South America that is affected by El Niño; parts of northwest US as well as the Midwest have also experienced low rainfall in winter because of El Niño. This is because El Niño currents are carried upward from the South American coast by Rossby waves – nomadic winds that move across the earth, picking up one region’s weather pattern and carrying it to another region.
Like the El Nino, the newly-formed Amazon dry-weather pattern could also be carried to and affect the northwest U.S., because the pattern would form several thousand miles earlier in the path of the Rossby waves than the El Nino, the researchers predict.
As El Niño already has noticeable effects on the US West Coast, it proved an ideal analog to help predict the effects of a barren Amazon on the same region, they state.
These findings indicate only one of many possible scenarios that may play out if the Amazon is completely destroyed. The Amazon basin currently feeds more than one-fifth of the world’s fresh water supply and contributes greatly to combating climate change. However, rampant deforestation coupled with global warming could wipe out the rainforest, if left unchecked.
Using high-resolution climate models, the researchers studied how weather characteristics such as rainfall, temperature and humidity would vary over time in an Amazon-less scenario.
Climate models divide the earth into grid cells, and use equations to project the values of weather characteristics at different points in the grid at different times. The smaller a grid cell (in terms of km or miles), the higher is the resolution. While most climate models typically have a resolution of 200 km, the researchers’ model could spot variations in weather characteristics at a much finer resolution of 25 km.
Studying these effects is important to understand the kind of impact destroying the Amazon can have on the global climate, and subsequently, agriculture and food supply in other parts of the world, the researchers believe.