Jan. 4 (UPI) -- The planet's drylands aren't getting drier as a result of global warming, according to a new study published Monday in the journal Nature Climate Change.
Scientists found a few key soil moisture-atmosphere feedback mechanisms are preventing Earth's drylands from becoming more arid.
Because a warmer atmosphere can hold more water -- accelerating evaporation across arid landscapes and encouraging precipitation across wet regions -- most scientists assumed climate change would cause Earth's dry regions to get drier and its wet regions to get wetter.
However, some of the more sophisticated climate models, known as coupled climate models, showed arid regions are unlikely to get drier in the short term. Until now, scientists didn't understand the contradiction.
To figure out why the "dry-get-drier and wet-get-wetter" theory failed to hold, researchers conducted several soil moisture experiments in their lab.
When scientists used statistical models to interpret their observations, they found long-term soil moisture changes and associated soil moisture-atmosphere feedbacks boast a previously underestimate impact on water availability in drylands.
"These feedbacks play a more significant role than realized in long-term surface water changes," lead study author Sha Zhou said in a news release.
"As soil moisture variations negatively impact water availability, this negative feedback could also partially reduce warming-driven increases in the magnitudes and frequencies of extreme high and extreme low hydroclimatic events, such as droughts and floods," said Zhou, a postdoctoral fellow at Lamont-Doherty Earth Observatory and the Earth Institute at Columbia University.
Without the negative feedback, Zhou said, the planet may see more frequent and more extreme droughts and floods.
When scientists used what they had learned about moisture-atmosphere feedbacks to predict the future of surface water availability under various global warming scenarios, they found dry areas over ocean are likely to get drier.
But the models showed drylands are likely to only grow marginally drier in the coming decades.
The contradiction is best explained by climate change's negative effect on soil moisture, the researchers said.
The new research showed declining soil moisture levels across Earth's drylands is likely to depress evapotranspiration and evaporative cooling, two mechanisms that enhance drying patterns.
With less of the two mechanisms at work, dryland surfaces are likely to heat up more quickly than wetter regions and ocean areas.
This is likely to strengthen air pressure differences between ocean and land and enhancing winds that carry water vapor from ocean to land, researchers said.
"Our work finds that soil moisture predictions and associated atmosphere feedbacks are highly variable and model dependent," said co-author Pierre Gentine.
"This study underscores the urgent need to improve future soil moisture predictions and accurately represent soil moisture-atmosphere feedbacks in models, which are critical to providing reliable predictions of dryland water availability for better water resources management," said Gentine, an engineer at Columbia's Earth Institute.