Plants Need Less Water as Climate Change Worsens

     (CN) — Researchers say rising carbon dioxide levels will make plants less thirsty, resulting in a drastic reduction of climate change-induced droughts.
     In a study led by the University of Washington, researchers presented findings of how reduced water requirements for nourishing plants could cut these global warming-based drought conditions by up to 50 percent.
     Their work will be published this week in the Proceedings of the National Academy of Sciences, an academic journal.
     The team explains that such an adjustment is largely overlooked in existing climate change models, which in turn present a grimmer projection than may actually be the case.
     “Plants matter. A number of studies assume that plant water needs are staying constant, when what we know about plants growing in lots of carbon dioxide suggests the opposite,” lead author Abigail Swann said.
     Recent studies have estimated that more than 70 percent of Earth will experience more drought as carbon-dioxide levels quadruple from pre-industrial levels over the next 100 years or so.
     However, Swan and her co-authors have accounted for the water needs of plants in the future, which suggests the actual figure is about 37 percent – with larger differences concentrated in certain regions.
     “It’s a significant effect,” Swann said.
     When Earth’s atmosphere holds more carbon dioxide, plants actually benefit from having more of the molecules that are needed to build their carbon-rich bodies.
     Plants use tiny openings that cover their leaves, called stomata, to absorb carbon dioxide. When carbon dioxide is more plentiful, the stomata doesn’t need to be open for as long, so plants lose less water — in turn leading the plants to draw less water from the soil through their roots.
     While global climate models already account for these adjustments in plant growth, many estimates of future drought use today’s standard indices — such as the Palmer Drought Severity index- which only consider atmospheric variables, including future temperature, precipitation and humidity.
     “I had a very strong suspicion that you would get a different answer if you considered how the plants were responding,” Swann said.
     The new study compares modern drought indices with ones that take into account changes in plant water use, confirming that reduced precipitation will increase droughts across southern North American, southern Europe and northeastern South America.
     On the other hand, the results also show that in Central Africa and temperate Asia — including China, East Asia, the Middle East and most of Russia — water conservation by plants will largely counteract the drought conditions stemming from climate change.
     The researchers say that planners will need accurate long-term drought predictions to establish future water supplies, project wildfire risks, anticipate ecosystem stresses and determine where to locate agricultural fields.
     “There’s a lot we don’t know, especially about hot droughts,” Swann said. “Even if droughts are not extremely more prevalent or frequent, they may be more deadly when they do happen.”

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