October 26, 2013
Amazon Rain Forest Dry Season 1 Week Longer Per Decade

Changes in the climate of the Amazon, most likely human caused, are making Amazonian dry seasons longer. Longer dry seasons translate into more fires and tree death.

A new study suggests the southern portion of the Amazon rainforest is at a much higher risk of dieback due to stronger seasonal drying than projections made by the climate models used in the latest report by the Intergovernmental Panel on Climate Change (IPCC). If severe enough, the loss of rainforest could cause the release of large volumes of the greenhouse gas carbon dioxide into the atmosphere. It could also disrupt plant and animal communities in one of the regions of highest biodiversity in the world.

Using ground-based rainfall measurements from the past three decades, a research team led by Rong Fu, professor at The University of Texas at Austin's Jackson School of Geosciences, found that since 1979, the dry season in southern Amazonia has lasted about a week longer per decade.

If the dry season gets too long then the rainforest will not survive.

To see why the length of the dry season is such a limiting factor, imagine there is heavier than usual rainfall during the wet season. The soil can only hold so much water and the rest runs off. The water stored in the soil at the end of the wet season is all that the rainforest trees have to last them through the dry season. The longer the dry season lasts, regardless of how wet the wet season was, the more stressed the trees become and the more susceptible they are to fire.

What I wonder: Could reservoirs be built to capture more of the rain during the wet season to release during the dry season? Even if this was done the water likely would not flow near most of the trees with the driest soil unless an elaborate irrigation system was built into the jungle.

A halt to deforestation would prevent some (all?) of the decline in rains. Reforestation would help even more. $1 billion per year would stop a tenth of deforestation. On present course deforestation might turn the Amazon into a desert. Urbanizing industrializing societies drive deforestation.

You might think the Amazon deforestation represents a large fraction of global deforestation. But no. Amazon deforestation is only 5 to 6% of global deforestation.

Share |      Randall Parker, 2013 October 26 12:49 PM 

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