The Arizona Republic

The effect of warming: One study suggests higher temperatur­es could lead to heavier monsoon rains in Arizona.

- LILY ALTAVENA

Arizona could experience heavier monsoon rains in the coming decades, according to the author of a new study examining rainfall changes around the world.

The study, published in the journal Science Advances, does not detail specific rainfall changes in Arizona.

But Aaron Putnam, its lead author and a geologist at the Climate Change Institute at the University of Maine, speculates that while there could be an “invigorati­on of the North American monsoon,” a warmer planet might also lead to a drop in precipitat­ion during the wintertime, potentiall­y reducing the snowfall that helps replenish water-storage reservoirs.

“The input of CO2 in the atmosphere is a bit of a sledgehamm­er on to the system,” he said. “It might respond in nonlinear, more unpredicta­ble ways.”

A heavier monsoon in the summer might be “flashy,” Putnam said, but less precipitat­ion in the winter would diminish water levels in aquifers and reservoirs critical to the state’s water supply.

Monsoon rains typically fall fast, while melting snow offers “a more sustained flow.”

The National Weather Service marks the start of the monsoon season today, though summer storms typically don’t begin to develop until late June or early July.

Putnam and his colleagues used geological archives to determine how precipitat­ion patterns will change with a warmer climate. From their research, they concluded that “wet areas will get wetter and dry regions will become drier.”

“The geologic record is trying to tell us something about how the system behaves,” he said.

In the study, the researcher­s also note that moisture will be directed north, away from the Sierra Nevada and the Great Basin, which spans much of the Intermount­ain West.

Last year’s monsoon yielded 2.49 inches of rain in Phoenix, but more critical to long-term water supplies is the snow that accumulate­s during the winter months and produces runoff for reservoirs come spring. The National Weather Service has recorded 96.7 inches of snowfall in Flagstaff since July of last year. Normal snowfall is 101.8 inches. The year before, snowfall was 78.3 inches.

Putnam thinks the state’s main challenge will be managing water as its accessibil­ity shifts.

“It’s really trying to come to grips with how water availabili­ty changes,” he said.

Environmen­tal coverage on azcentral.com and in The Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmen­tal reporting team at OurGrandAZ on Facebook, Twitter and Instagram.

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