The Next Eco-Crisis: 'Evapotranspiration'


Evapotranspiration is what happens when water in and on the ground, or extracted from the ground by plants during transpiration, moves into the atmosphere, creating the potential for rain or other forms of precipitation.  

Across some of the earth, this cycle is in serious disarray, according to a report cited by ScienceDaily, which notes that the imbalance began in 1982 and continued into the 1990s, after which the rate of evapotranspiration slowed.  

Slowing didn’t mean improvement, however. In fact, in the areas surveyed (Australia, Africa, South America, and parts of China, India and Indonesia), desertification – the consequence of failed evapotranspiration activities – continues unabated, presumably because some critical tipping point has been reached. 

And, while researchers from a consortium of respected institutions (the Max Planck Institute; the Institute for Atmospheric and Climate Science; Princeton, Harvard and Oregon State universities; and the National Center for Atmospheric Research) admit that they don’t have enough data, collated over a long-enough period, to draw any firm conclusions, all seem certain of one thing; parts of the globe are getting notably drier, and the consequences for humans living there could be serious. 

Under normal circumstances, evapotranspiration accounts for about 60 percent of an area’s annual precipitation, with solar insolation absorbed by land surfaces creating the energy needed for the transfer (and thus linking the earth’s hydrological and carbon cycles).  

Scientists have long suspected that climate change, also known as global warming, would alter the normal patterns of evapotranspiration, and research published in the October issue of Nature, an online science journal, demonstrates exactly that.  

According to lead author Martin Jung, evapotranspiration rates in some areas have entered a sort of negative feedback loop. Ironically, other areas seem to be getting much wetter, making food growing equally precarious, and the division into wet and dry seems to fall along the Equator, with the northern half wetter and the southern half drier. Clearly, the Earth itself is out of balance (the interpretation is mine).  

The conclusion – that an upper limit to the acceleration of the hydrological cycle on land has already been reached – leads to another, and more disturbing conclusion. As the cycle tips precariously into the red, larger and larger landmasses could become irretrievably parched, making it impossible to grow food and leading to more frequent or extreme heat waves.  

The data for the study was collected via FLUXNET, a global network of about 500 meteorological monitoring devices. Beverly Law, a forest science professor at Oregon State University and co-author of the study, is science director of AmeriFlux, the N. American portion of the FLUXNET network.

Incorporating carbon and water vapor exchange data from around the world, Jung, Law and others want to refine information, presented in February of this year by the International Journal of Life Cycle Assessment, which shows that 38 percent of the world is now comprised of arid regions increasingly at risk of desertification of the evapotranspiration tendency continues.  

Perhaps the worst bit of news from the earlier report is that unsustainable land use practices (large-scale farming, logging, biofuels, tree plantations and the like) may lead to irreversible soil degradation, according to Montserrat Núñez, a researcher at the Institute of Agro Food Research and Technology (IRTA) based in Catalonia, Spain. In any case, the dual reports highlight the ineffectiveness of the UN Convention to Combat Desertification, which – though active since 1996 – has so far failed to stem the tide of deserts encroaching on mankind.  

And the newest report, by the National Center for Atmospheric Research on desertification, shows that these drier conditions will increase across much of the planet in the next three decades, possibly reaching a scale that has “rarely, if ever, been observed in modern times.”  

Technology may come to the rescue, as food scientists engineer hardier, more drought tolerant varieties of staple grains like wheat, rice and corn. So many hydrological advances which aim to prevent evapotranspiration by using mulch and impermeable groundsheets under plants. But genetically modified foods à la Monsanto have already proved themselves a “flash in the pan” (an expression coined during 1848 California Gold Rush, when many miners staked worthless claims based on single flash of gold in their sluice pans).  

The only question remaining is whether sufficient technology will arrive in the world’s in-basket in time to save the poorest. If not, the question will become moot.

Read more on Celsias:

A Cool Roof Could Offset Carbon Emissions

Gaia in Turmoil

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  • Posted on Oct. 21, 2010. Listed in:

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