New research connects forests to stabilizing rainfall

• February 1, 2013

Forest, Creative Commons: Rodrigo Sala, 2008

At the Center for International Forestry Research (CIFOR), scientists are gathering evidence for a new hypothesis that gives greater importance to the role of forests in regulating local humidity and rainfall.

The hypothesis would reinforce the connection between the biology of living systems and the physics that cause local weather patterns.  It would also bring renewed urgency to the need to protect large forests in order to stabilize local climates.  An elaboration of the hypothesis could be used to determine if strategically planting forests near drought-stricken regions could encourage rainfall for the benefit of nearby communities.

“This theory provides us with yet another reason to protect and conserve forest cover,” said Douglas Sheil, co-author of the paper published in Atmospheric Chemistry and Physics and a Senior Associate with CIFOR.

When water evaporates from the earth’s surface, it pulls air and moisture higher up into the atmosphere, which causes more moist air to be pulled across to replace it.  This creates a pump-like circulation system.

Plant life can impact this circulation, a process that the authors call the biotic pump model.  High rates of evaporation occur in heavily forested areas, encouraging the circulation of moisture from oceans inland towards forests.  In desert areas, rates of evaporation are much lower, meaning that moisture circulates in the opposite direction – away from deserts and towards the oceans.  These physical processes are integral in maintaining the characteristic humidity, rainfall, and winds of various biomes.

If a forest loses enough of its greenery due to outside factors – such as climate change or human deforestation – the cycle can switch directions to look more like what is occurs over deserts.  Loss of plant life lowers rates of evaporation, and moist air begins to circulate towards oceans and away from the land.  This hypothesis implies that deforestation intensifies drought and low rainfall patterns, and enough deforestation could create a tipping point past which moisture would be pulled away from areas that are historically very humid.

Continued research into this process will likely reinvigorate the conservation mission of World Bank programs that incentivize forest protection.

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About the Author

Emily is a graduate of St. Mary's College of Maryland with a B.A. in psychology. While in school, she spent her time leading environmental and social justice campaigns. She recently worked for the Chesapeake Climate Action Network as a grassroots organizer for a moratorium on natural gas fracking in Maryland.

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