Southwest is getting drier

Southwest is getting drier

A new report from several hundred scientists emphasizes the impacts already being felt across the Southwest. A federally funded study says broad storm patterns associated with precipitation have occurred more rarely in the region over a recent 35-year span.

The weather patterns that typically bring moisture to the Southwest are becoming more rare, an indication that the region is sliding into the drier climate state predicted by global models, according to a new study.

A normal year in the Southwest is now drier than it once was, said Andreas Prein, a researcher at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, who led the study. If you have a drought nowadays, it will be more severe because our base state is drier.

Just think of California drought, the type of hot, snowless, severe drought that we expect more of in the future, Gregg Garfin, a lead author of the Southwest portion of the National Climate Assessment and assistant professor of climate, natural resources, and policy at the University of Arizona, stated earlier.

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

In the new study, published in the journal Geophysical Research Letters, a publication of the American Geophysical Union, researchers grapple with the cause of current drying in the Southwest to better understand how it might be connected to a warming climate.

For the study, the researchers 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.

They identified a dozen patterns that are usual for the weather activity in the contiguous U.S., then looked to see whether those 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, Prein said. Because only a few weather patterns bring precipitation to the Southwest, those changes have a dramatic impact.

The Southwest is especially vulnerable to any additional drying. The region, already the most arid in the country, is home to a quickly growing population that is putting tremendous stress on its limited water resources.

Prolonged drought has many adverse effects, so understanding regional precipitation trends is vital for the well-being of society, says Anjuli Bamzai, program director in the National Science Foundation (NSF) Division of Atmospheric and Geospace Sciences, which funded the research.

Understanding how changing weather pattern frequencies may impact total precipitation across the U.S. is particularly relevant to water resource managers as they contend with issues such as droughts and floods, and plan future infrastructure to store and disperse water, said NCAR scientist Mari Tye, a co-author of the study.

To examine this potential connection further, they are studying climate model data for evidence of similar changes in future weather pattern frequencies.

Southwest is getting drier