The worst-case scenario in Prescott’s weather future: average temperatures more than 10 degrees warmer than present with precipitation levels that would be unlikely able to keep up from year to year, according to an area climatologist.
Dr. Michael Crimmins, climate science extension specialist and associate professor at the University of Arizona, discussed climate models and the state’s shifting weather during the Citizens Water Advocacy Group meeting on Saturday, Feb. 9.
Crimmins’ talk, titled “Drought in Arizona: Observations, Impact, Projections,” discussed the unique aspects of Arizona’s hydroclimate that control precipitation variability in the long and short terms.
On average, shifts in temperatures will shift water balance, he said. Though it is tough to look at the component of temperature driving where the water balance is in a given year, over the decades it can be said that the water balance should have shifted in response to warmer temperatures, Crimmins said.
“As it gets warmer, it needs to rain more here to not have the water balance shift,” he said.
Climate models project similar if not higher variability and higher uncertainty for the area in the future and lead to the worst-case scenario, Crimmins said. Warmer temperatures by the end of the century with not much change to the annual average precipitation would lead to shifts in the water balance, Crimmins said. In some years, precipitation could keep up, but on average, over time it probably couldn’t, he said.
“You get a wet year from the beginning of the year to the end of the year and it was cool, you will see some … positive change in water, but then what’s the next year going to look like?” he said. “You can erase that pretty quickly.”
Crimmins said the hydroclimate of Arizona is made up of a variety of parts. Those parts include topoclimate, climate related to topography; seasonality with the idea of monsoons vs. winter storms, something other parts of the country don’t have, and the El Niño-Southern Oscillation, which drives changes in the winter jet stream based on its seesawing between El Niño and La Niña years, Crimmins said.
“It can lead us into a wet winter or into a very dry winter,” he said. “Last winter was a La Niña … last winter was a very, very dry winter.”
Another part is climate change and background subtle changes primarily in temperature, Crimmins said. Right now, creeping warming temperatures are driving subtle shifts in the background water balance, but in the long term it could cause some shifts and changes such as El Niño becoming stronger, he said.
He also explained how increasing temperatures relate to drought conditions and explored various climate model projections and what they mean in terms of changes in temperatures and precipitation patterns.
When it comes to using weather timescales as to what can happen in Arizona, the time from October 2017 until recently is actually a good case study, Crimmins said.
The beginning to October 2017 came off of a pretty good summer before moving into a record warm and record dry October, November and December, he said. Through May 31, 2018, it rained 16 days for a total of 2 1/3 inches with most of it being in May, Crimmins said.
“It was the driest October through May on record from 1962 to 2018 and the third warmest,” he said. “If it stood out as unusual to you, you weren’t making it up.”
Then, the 2018 monsoon season hit and provided strong, frequent monsoon activity through August with 12.2 inches, making it the ninth wettest and seventh warmest on record, Crimmins said. It was then mixed from the beginning of October through January, he said. October saw tropical storms, November and most of December was dry until the holidays when a “normalish” Arizona winter came in with cold and wet storms with snow levels through the early part of January, Crimmins said.