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May 26, 2022, 10:55 a.m. EDT

Grim drought outlook for Western U.S. in 2022 offers warnings for the future as climate change brings a hotter, thirstier atmosphere

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By Imtiaz Rangwala

Much of the western U.S. has been in the grip of an  unrelenting drought  since early 2020. The dryness has coincided with record-breaking  wildfires , intense and long-lasting  heat waveslow stream flows  and  dwindling water supplies in reservoirs  that millions of people across the region rely on.

Heading into summer, the  outlook  is pretty grim. The National Weather Service’s  latest seasonal outlook , issued May 19, described drought persisting across most of the West and parts of the Great Plains.

One driver of the Western drought has been  persistent La Niña conditions  in the tropical Pacific since the  summer of 2020 . During La Niña, cooler tropical Pacific waters help nudge the jet stream northward. That tends to bring  fewer storms to the southern tier of the U.S.  and produce pronounced drought impacts in the Southwest.

The  other  and perhaps more important part of the story is the  hotter and thirstier atmosphere, caused by a rapidly warming climate .

As a  climate scientist , I’ve watched how climate change is making drought conditions increasingly worse—particularly in the western and central U.S. The last two years have been more than 2 degrees Fahrenheit (1.1 Celsius) warmer than normal in these regions. Large swaths of the Southwest have been even hotter, with temperatures more than 3 F (1.7 C) higher. 

Studies suggest the Southwest’s ongoing 20-year drought  is the most severe in at least 1,200 years, based on how dry the soils are.

A hotter atmosphere sucks more moisture from the soil

A thristier atmosphere tends to extract more water out of the land. It exacerbates  evaporative stress  on the land, particularly when a region is experiencing below-normal precipitation. High evaporative stress can rapidly deplete soil moisture and lead to hotter temperatures, as the  evaporative cooling effect  is diminished. All this creates hydroclimatic stress for plants, causing restricted growth, drying and even death.

As a consequence of a warming climate, the U.S. Southwest has seen an 8% increase in this evaporative demand since the 1980s. This trend is generally  happening across other parts of the country .

The  thirstier atmosphere  is turning what would otherwise be near-normal or moderately dry conditions into droughts that are more severe or extreme. As the climate heats up further, the increasing atmospheric thirst will continue to intensify drought stress, with consequences for water availability, long-lasting and intense heat stress, and large-scale ecosystem transformation.

Climate models project ominous prospects of  a more arid climate and more severe droughts  in the Southwest and southern Great Plains in the coming decades.

In addition to direct impacts of increasing temperatures on future droughts, these regions are also expected to see  fewer storms  and  more days without precipitation . Climate models consistently project a  poleward shift in the midlatitude storm tracks  during this century as the planet heats up, which is expected to result in fewer storms in the southern tier of the country.

Expect flash droughts even in wetter areas

The changing nature of droughts is a concern  even in parts of the U.S. that are expected to have a net increase  in annual precipitation during the 21st century. In a hotter future, because of the high evaporative demand on the land, prolonged periods with weeks to months of below normal precipitation in these areas can lead to significant drought, even if the overall trend is for more precipitation.

Large parts of the northern Plains, for example, have seen precipitation  increase by 10% or more  in the last three decades. However, the region is not immune to severe drought conditions in a hotter climate.

At the tail end of what was the  wettest decade  on record in the region, the northern Plains experienced  an intense flash drought in the summer of 2017  that resulted in agricultural losses in excess of $2.6 billion and  wildfires  across millions of acres.  Record evaporative demand  contributed to the severity of the flash drought, in addition to a severe short-term precipitation deficit.

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