Weather and climate in the Southwest: Part Two
This is Part Two of a two-part discussion with Arizona’s top weather climatologists about the long (and continuing) drought in the Southwest, the reasons behind the abundant moisture during the 2016-2017 winter and expectations for the future (cross your fingers!).
In today’s feature we talk with Mark O’Malley, forecaster and Climate Science Program manager for the National Weather Service.
Published on March 8, Part One featured an interview with Arizona State Climatologist Nancy Selover. Dr. Selover is the Julie Ann Wrigley Global Institute of Sustainability Research Professor at Arizona State University’s School of Geographical Sciences and Urban Planning in the College of Liberal Arts & Sciences.
Selover and O’Malley are the co-chairs of the State Drought Monitoring Technical Committee, which is responsible for gathering and analyzing data regarding Arizona drought, climate and weather.
The information they provide is used by the Governor’s Interagency Coordination Group, which makes an annual recommendation to the Arizona Governor about whether the state’s long-running state of drought should be extended. Or… not. Arizona Department of Water Resources Director Tom Buschatzke co-chairs the ICG.
Climate science – a field of study that has evolved rapidly in this century – examines a phenomenon like “drought” from an increasing number of factors.
For one thing, it makes the recommendation to the governor on whether to continue the drought declaration more precise.
Drought impacts can range from a lack of soil moisture, affecting range land and farming, to water levels in the state’s reservoirs. And all of the factors that climatologists weigh when deciding whether drought exists can vary widely in time and scale. But all the drought factors taken together make it more difficult to establish with certainty when a drought may begin or end.
“I think it’s generally accepted that Arizona is in a standing, long-term drought since 1999,” said Mark O’Malley of the National Weather Service.
“But clearly there are years and parts of years in the past 17 years where drought has been less expansive and less intense. There really is no good way to say drought in Arizona started on ‘x’ day in 1999.”
Like State Climatologist Nancy Selover – O’Malley’s co-chair on the State Drought Monitoring Technical Committee – O’Malley sees the effects of the very wet 2016-2017 winter as a real positive for most of Arizona. But the slowly improving drought conditions locally are impacted by the summer monsoons, too, he notes.
“We have experienced three to four excellent summer monsoon seasons where thunderstorms and rainfall across the state have been quite good, but we've also had five consecutive winters with below average snow in the mountains,” said O’Malley. And it is that snowpack in the mountains that is important for the state’s water supply.
“This winter has been good -- especially around the Flagstaff area -- but doesn't totally compensate for the five previous dry winters.”
In terms of moisture, “good” in Arizona consistently is less good than on the California coast, where unprecedented winter moisture largely has ended that state’s drought. There are a number of reasons for that phenomenon, says O’Malley. Some are atmospheric. Some are geographic.
For one, he notes, central and northern California are at higher latitudes than Arizona, and so more commonly fall under the jet stream – which also explains why even during the sodden 2016-2017 winter, Los Angeles and San Diego are getting less moisture than, say, Sacramento.
Then there is the effect of those mountains separating the coastal cities from Phoenix, which, among other things, tends to wring out moisture from those Pacific storms as they sweep inland.
“Moisture from the Pacific streams unencumbered into the coastal cities with lift provided by air flowing over the mountains providing even more rain and snow,” said O’Malley.
“As the air flows over the mountains into far southeastern California and Arizona, it sinks. And you generally need air rising to produce precipitation.”
Often, he notes, there is “nothing left over for Arizona” in those storms. “This is why the deserts from Yuma through Death Valley, Calif., are the driest places in the United States.”
With California reservoirs literally overflowing and with Los Angeles Mayor Eric Garcetti calling for a state of emergency as a result of the melting snowpack in the eastern Sierra Nevada, California is confident – for now, at least – that it is nearly free of drought.
What about Arizona?
“By both objective measures and impacts, drought in Arizona is certainly better -- which is to say, we have less drought -- than last year at this time, and substantially better than two to three years ago,” said O’Malley.
“I wouldn't go as far as using the term ‘waning’ -- that word infers a resolution or termination in the immediate future.”
It doesn’t take much for an arid state to slip back into serious, widespread drought conditions.
“Bottom line, because of our location, growing population, and demand for water, Arizona will always be susceptible to drought.”