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US Southwest May Be Drying Up As Wet Weather Systems Become More Rare

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The southwestern United States may be sliding more quickly into drier climates as the regions' typical moisture and wet weather systems are becoming increasingly rare, a new study revealed.

What is considered as the normal amount of rain and snow in the Southwest is actually drier now than what it was once, researchers from the National Center for Atmospheric Research (NCAR) found.

"If you have a drought nowadays, it will be more severe because our base state is drier," said Andreas Prein, the lead author of the study.

Previous climate models generally indicate that human-induced climate change will push the Southwest to become drier, and in recent years, the area has been afflicted by drought. However, associating climate models to changes on the ground is not easy.

NCAR researchers delved deeper into the underlying cause of drying conditions in the Southwest in order to understand how it might be linked to a warming climate. They studied 35 years of meteorological data to detect common weather patterns and determine whether these patterns were more or less frequent over time.

What they found are consistent with climate models that predict human-made climate change will push a belt of drier high pressure to areas near the equator: Los Angeles, San Francisco, Las Vegas, Albuquerque, Cheyenne, Salt Lake City, Phoenix and Wyoming.

Last year, researchers from Cornell University used climate models to predict chances of droughts in the Southwest. It turns out that the region has a 50 percent chance of experiencing a "megadrought" in the coming decades, all of which could last up to 35 years.

Toby Ault, leader of the Cornell study, said the megadrought will be worse than anything that occurred in the last 2,000 years. It would also pose unprecedented difficulties to water resources in the Southwest.

Meanwhile, NCAR researchers calculate an opposite, albeit smaller, effect in northeastern United States, where levels of precipitation appear to be increasing.

"This study is important as it connects the dots between long-term trends and changes in specific weather patterns that appear to be driving those trends," said Texas Tech climate scientist Katharine Hayhoe, who wasn't part of the study.

The findings of the NCAR study are published in the journal Geophysical Research Letters.

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