Climate change adds new variables to forecasting the monsoon

2022-06-15 14:34:37 By : Mr. Kit Wong

The monsoon season starts officially across the Southwest on Wednesday. But even as it unfolds, what that will mean for Arizona this year is still pretty much anyone's guess.

What's known as the North American monsoon typically begins in early June in central and southern Mexico. It forms when summer heat results in a build up of atmospheric pressure that forces a shift in the predominant winds, from westerly (blowing from the west) to southerly (blowing from the south). These winds push air holding evaporated moisture from the Pacific Ocean and the Gulf of California over northern Mexico, New Mexico and Arizona, where it falls as rain, often in dramatic thunderstorms.

The monsoon rain that falls in Arizona during the season through September makes up around half of the state's annual precipitation. It's an essential source of moisture for wildlife, plants, agriculture and the reservoirs that supply drinking water the rest of the year.

But the blessing is mixed. Heavy monsoon rains flood neighborhoods and roads, which become hazardous, even deadly to cross. They cause power outages and property damage. And they create pools of standing water where mosquitos breed and spread disease.

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The Phoenix office of the National Weather Service estimates that there are half a million lightning strikes that ignite more than 2,000 wildfires in Arizona each season. Monsoon storms also bring a variety of other bizarre and often amusingly named weather threats, including haboobs, downbursts, gustnadoes, earth fissures and landslides.

For all of these reasons, Gov. Doug Ducey has declared June 13-19 Monsoon Awareness Week. And the Arizona Emergency Information Network, the National Weather Service and other agencies have assembled information on how to stay safe while weathering all of the upcoming season's various moods.

What's not included in these presentations is much guidance on what kind of monsoon temperament to expect.

Earlier this year, predictions were for the 2022 monsoon to be wetter than normal, following an especially dry monsoon in 2020 and an exceptionally wet season in 2021.

But as the season opens, a video produced by the National Weather Service explains that "the Climate Prediction Center precipitation outlook for this monsoon favors equal chances for near, below or above-normal rainfall across Arizona." To be specific, the center estimates a 35% chance that southern Arizona will see above-average precipitation during the 2022 monsoon, a 33% chance it will be normal and a 32% chance it will be below normal. The odds for northern Arizona are split 33%, 34% and 33%.

That's not exactly helpful. So why is it so hard to predict what the monsoon has in store for Arizona?

Gaps in meteorologists' understanding of monsoon systems is not for lack of skill or effort. A legion of climate and atmospheric scientists have studied drivers of monsoonal patterns, anticipating the importance of these forecasts for water planning in the drought-stricken Southwest where Colorado River allocations are already hotly contested.

They've assembled research teams, datasets and statistical models that require the latest in computational power, and then published studies that, with a lot of technical terminology, generally conclude that no one can say with much detail or certainty what's going to happen with the North American monsoon under a warming climate.

What one paper published in 2019 in the journal Monsoons and Climate did suggest, after compiling results from recent studies, is that future monsoons may consist of sparser, more sporadic and stronger storms over Arizona. The same amount or slightly less rain falling on fewer occasions will result in more flood damage and less absorption into the soil. Thunderstorms may also be more likely to occur in Arizona's mountains, causing the wetter parts of the state to get wetter while the desert gets drier.

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As for this year, it's still hard to be sure.

"It is very difficult to predict the monsoon season," said William Boos, an atmospheric scientist and associate professor of Earth and Planetary Science at the University of California, Berkeley, who has co-authored papers about monsoon forecasting. 

"Seasonal prediction of climate is actually something that is still in its infancy. So, I think that if there is a prediction for a wetter than normal 2022, I would view that as a prediction that is not going to be very confident."

This lack of self confidence in their own monsoon predictions is not an indication that scientists aren't sure if they know what they're doing. Rather, it's a reflection of how complicated our atmosphere is and how impossible it is for anyone, regardless of training, teamwork or computing power, to see into the future.

“There’s kind of two different topics here," said Paul Iñiguez, a meteorologist and the science operations officer at the Phoenix NWS office. "You’re talking about projections of monsoons and how they fit into a warming climate several decades down the road. And then you’re also talking about predicting what’s going to happen with this year’s monsoon. And that’s a totally different process."

His office mostly focuses on weather forecasts in the more immediate future, Iñiguez said, usually for the next seven days. At that point, you're more zoomed-in on the problem and you have more information about what the conditions already are and what they have been recently that can guide conclusions about what might happen next.

Weather forecasts for the next week may be more likely to be accurate than climate projections for the next decade. Or they might not be. It depends on how specific the forecaster is trying to be.

Iñiguez likens weather to the mood you're in on any given day, whereas climate is more like your personality, those underlying behavioral tendencies that play out over longer periods of time. Exactly where the distinction is between what constitutes a weather forecast and when it crosses over into a climate projection is a matter of internal debate within the scientific community.

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What is certain is that, as soon as you try to zoom in on atmospheric phenomena, by trying to look closer at a specific time or place or pattern, the image gets grainy.

"A monsoon is a pretty grand-scale pattern of winds and atmospheric circulation that draws in water vapor from ocean regions and deposits it in the form of rainfall on different continents," said Boos. "So it's actually a lot easier, it's a better formulated problem, to simulate and then project future variations in than it is to be confident about some individual cloud or thunderstorm."

Leila Carvalho is a professor and climate scientist at the University of California, Santa Barbara, who also tries to peak into the monsoon future and was a co-author of the 2019 paper in Monsoons and Climate. She further underscored the distinction between weather predictions and climate projections, and said it all matters for our ability to plan for what's ahead.

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“A projection is usually something we expect to see over time, a trend. But from year to year, this will be a little different because there are other phenomenon occurring that will be part of the natural variability, so you’ll see a trend but also a lot of fluctuation," Carvalho said.

"Our brains are not organized to process things too far ahead. But that’s the distinction that people need to understand. If you are a decision-maker, if you are a politician planning for Arizona’s future, you have to look at both."

Psychologists agree that holding two opposing thoughts in your head at the same time is a difficult but important skill.

“People think that 'Oh, because it rained yesterday or it was cold, there’s no climate change and warming doesn’t exist,'" said Carvalho. "That’s the confusion that happens, because we humans perceive things with our instincts and our instincts are short term. But we have to start training our brains to think about the future and the present at the same time."

Data can help. In Arizona, conditions in recent decades have trended warmer and drier. Scientists know this to be largely due to the increase in atmospheric concentration of greenhouse gases, mostly a result of burning fossil fuels, that hold more heat in the air and result in increased evaporation and drier soils.

As calculated by the policy-neutral nonprofit Climate Central, the average local summer temperature in Phoenix has has increased by 3.6 degrees Fahrenheit (2 degrees Celsius) over the past 50 years. There are nine more days per year when local highs exceed 110 degrees. The average summer overnight low has gone up 5.5 degrees.

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Some of this is due to the urban heat island, where the concrete and asphalt of rapid development retain more heat than natural surfaces. But scientists understand about half of the observed warming to be due to the effects of climate change. 

A warmer climate means more energy in the atmosphere and more extreme, chaotic weather events. With the past nine years among the Earth's top 10 hottest on record, according to the National Oceanic and Atmospheric Administration, natural disasters like massive wildfires, flooding, hurricanes and ice storms have become regular events.

"We have now a climate on steroids," said Carvalho. "If you have a player in baseball or basketball and they start taking steroids, the game is the same, the rules will not change, but that player, because he took the steroids, will jump higher and run faster."

"What causes rainfall doesn’t change. We know the rules of the game. The problem is, we start giving steroids to the players and then, when it’s their time to play, they do a lot more than they would normally. That’s how the game is changing."

Boos sees it in Kentucky Derby terms. As a society, scientific models can help us place bets on the most likely winner out of a fixed set of monsoon scenarios and plan for that end result. But we should be aware that there are other options at play and prepare for different outcomes. We can't afford to put all our resources into one best-case scenario, especially with climate change working against us.

"If I go to a horse race, certain horses may be more likely than others to win, right? If you want a good monsoon climate — adequate rainfall, not drought — that's the probability of a certain horse winning," Boos said.

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"As the climate gets warmer, it's going to become less and less likely that your favorite horse is going to win. Even though we don't know what's going to happen with the rain, we do know that we're evaporating more water. That's like (how) you maybe don't know what's going to happen with the jockey, but you know that a horse's health is declining. So, how are you going to change your bets?"

That's why Carvalho says it's time for the Southwest to prepare not only for this season starting on Wednesday, but for the effects future monsoons will have on society.

Major concerns will be water availability, wildfires and agriculture, she says, especially in Indigenous communities that don’t have as many ways to change or cope. Home insurance against natural disasters is also a growing challenge that will likely hit hard in Arizona.

"In recent years, we have had floods and hurricanes and wildfires displacing people," Carvalho said. "The number of homeless people has grown exponentially. Where are they going? They don’t go to places like Minnesota or Chicago or North Dakota because they can’t survive. They are coming to the West Coast and to the Southwest."

The horse to bet on, in this case, is working together to slow the climate crisis, experts say. Guidelines laid out by recent reports from the Intergovernmental Panel on Climate Change outline how.

“We need to deal with the energy crisis and the water crisis and figure out how we are going to deal with those things for the people living on this planet," she said. "This is a problem for everybody, every color, red or blue or green."

As the monsoon kicks off in Arizona, the lesson climate experts have gleaned from data and statistical models is that the world is complicated. Weather is complicated. Climate is complicated. Answers aren't always simple. But, much like psychologists suggest, the solution may lie in learning to "live in the messy gray."

Joan Meiners is the climate news and storytelling reporter at The Arizona Republic and azcentral. Before becoming a journalist, she completed a doctorate in ecology. Follow Joan on Twitter at @beecycles or email her at