New study from the National Center of Atmospheric Research predicts the western US will be much drier in just 20 years
By Summit Voice
SUMMIT COUNTY — The western two-thirds of the U.S. and many other mid- and low-latitude regions of the world could be much drier as soon as the 2030s, according to a new study from Aiguo Dai, a scientist with the National Center for Atmospheric Research in Boulder.
Drought may reach a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times, Dai said, cautioning that the findings are based on the best current projections of greenhouse emissions. What happens in coming decades will depend on many factors, including actual future emissions of greenhouse gases as well as natural climate cycles such as El Niño, NCAR said in a press release announcing the findings.
The report uses an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies to predict that dryness probably will increase substantially across most of the Western Hemisphere, along with large parts of Eurasia, Africa, and Australia.
Dai turned to results from the 22 computer models used by the IPCC in its 2007 report to gather projections about temperature, precipitation, humidity, wind speed, and Earth’s radiative balance, based on current projections of greenhouse gas emissions.
He then fed the information into the Palmer model to calculate future drought conditions. A reading of +0.5 to -0.5 on the index indicates normal conditions, while a reading at or below -4 indicates extreme drought.
He concluded that, by later this century, many of the world’s most densely populated regions will be threatened with severe drought conditions. In contrast, higher-latitude regions from Alaska to Scandinavia are likely to become more moist.
“This research does an excellent job of placing future warming-induced drought in the context of the historical drought record,” says Eric DeWeaver, program director in NSF’s Division of Atmospheric and Geospace Sciences. “The work argues credibly that the worst consequences of global warming may come in the form of reductions in water resources.”
“We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community,” Dai says. “If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous.”
Other countries and continents that could face significant drying include:
• Much of Latin America, including large sections of Mexico and Brazil
• Regions bordering the Mediterranean Sea, which could become especially dry
• Large parts of Southwest Asia
• Most of Africa and Australia, with particularly dry conditions in regions of Africa
• Southeast Asia, including parts of China and neighboring countries
• The study also finds that drought risk can be expected to decrease this century across much of Northern Europe, Russia, Canada, and Alaska, as well as some areas in the Southern Hemisphere.
However, the globe’s land areas should be drier overall.
“The increased wetness over the northern, sparsely populated high latitudes can’t match the drying over the more densely populated temperate and tropical areas,” Dai says.
Previous climate studies, including the 2007 assessment by the Intergovernmental Panel on Climate Change concluded that subtropical areas will likely have precipitation declines, with high-latitude areas getting more precipitation.
In addition, previous studies by Dai have indicated that climate change may already be having a drying effect on parts of the world.
He and colleagues found that the percentage of Earth’s land area stricken by serious drought more than doubled from the 1970s to the early 2000s. Last year, he headed up a research team that found that some of the world’s major rivers are losing water.
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