Southwest Climate is Changing as Weather Patterns Fail to Bring Moisture

It turns out that the southwest may just have shifted to a drier climate. Scientists have found that the weather patterns that typically bring moisture to the southwest are becoming rarer, which is an indication that the region is sliding into the drier climate state predicted by global models.

"A normal year in the southwest is now drier than it once was," said Andreas Prein, one of the researchers, in a news release. "If you have a drought nowadays, it will be more severe because our base state is drier."

Climate models generally agree that human-caused climate change will push the southwestern United States to become drier. In recent years, the region has been stricken by drought. But linking model predictions to changes on the ground is challenging.

In this latest study, the researchers examined the cause of the current drought in the southwest. They analyzed 35 years' worth of data to identify common weather patterns-arrangements of high and low pressure systems that determine where it's likely to be sunny and clear or cloudy and wet. In all, they identified a dozen patterns that are usual for the weather activity in the contiguous U.S. and then looked to see whether these patterns were becoming more or less frequent.

"The weather types that are becoming more rare are the ones that bring a lot of rain to the southwestern United States," said Prein. "Because only a few weather patterns bring precipitation to the southwest, those changes have a dramatic impact."

The findings reveal that the subtle shifts in large-scale weather patterns over the past three decades or so have been the dominant factor in precipitation trends in the southwestern United States, which could be huge in determining future climate.

The findings are published in the journal Geophysical Research Letters.

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