What is "Evapotranspiration" And How Is It Changing Our Planet?

cracked land photo

Photo via Noel Feans via Flickr Creative Commons

New research from Oregon State University shows that trends in evapotranspiration is having incredibly significant impacts on everything from our planet's vegetation growth to carbon absorption to natural cooling systems. But what in the world is "evapotranspiration" and why does it have such a huge effect on the earth's systems?

evapotranspiration graphic image

Image via wikipedia
Evapotranspiration in its most basic sense is the transfer of water from the land surface through vegetation to the atmosphere. It is part of the natural water cycle and occurs with evaporation and as plants lose water to the air.

Everything was humming right along until around 1998, as researchers noted that the cycle of evapotranspiration suddenly changed, from increasing as the global temperature warmed to slowing or even stopping. According to new research, soils are releasing less water than usual into the atmosphere. Rather than continuing to speed up as was expected with warmer temperatures, large areas of land especially in already arid places like Africa, are drying up.

Those studying evapotranspiration aren't sure why the shift has occurred, and whether it is a natural cycle or part of a larger global change. But even though they don't know why it's happened, scientists do know that the consequences could be big.

They could include reduced terrestrial vegetation growth, less carbon absorption, a loss of the natural cooling mechanism provided by evapotranspiration, more heating of the land surface, more intense heat waves and a "feedback loop" that could intensify global warming.

"This is the first time we've ever been able to compile observations such as this for a global analysis," said Beverly Law, a professor of global change forest science at Oregon State University. "We didn't expect to see this shift in evapotranspiration over such a large area of the Southern Hemisphere," Law said. "It is critical to continue such long-term observations, because until we monitor this for a longer period of time, we can't be sure why this is occurring."

Changes in the water cycle due to global shifts in temperature are becoming more apparent in several areas. As temperatures warm and the salinity of our oceans change, our water cycle seems to become intensified. Also, our tropical rainbelt is shifting farther north, which will shift everything from rainforest concentrations to species locations. Unfortunately, much of how our water systems are changing and what those shifts will mean is a wait-and-see process.

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More on Changing Rainfall Cycles
Ocean Saltiness Shows Global Warming Is Intensifying Our Water Cycle
Can the Watercycle Help Africa Survive? (Washington State University)
An Explanation of the Water Cycle (with Pictures and Diagrams)

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