Monsoon is set to unleash flooding rains in drought-stricken Arizona

By Judson Jones and Hannah Gard, CNN

The punishing heat wave continues in much of the West. However, for some in places in the Southwest including Arizona, the long-awaited monsoon will bring milder temperatures and rainfall.

It may just arrive a little bit too fast, raising flash flooding concerns in the area.

“Afternoon and evening showers and storms are expected to be in place across the Four Corners region, and especially southern Arizona and New Mexico, as the southwest monsoon kicks into high gear,” the Weather Prediction Center said Tuesday morning.

Rainfall amounts of anywhere from a half inch to 1 inch are possible, said the National Weather Service in Phoenix. Upper-end amounts of 2 to 4 inches aren’t out of the question.

“Given relatively weak steering flow aloft, many of these storms will likely be slow moving and result in flash flooding for canyons, across burn scars, and other vulnerable areas,” the prediction center said.

This has prompted the weather service to issue flash flood watches Tuesday afternoon through Wednesday morning for portions of Arizona, including the Phoenix metro area.

Flash flooding is very typical during these monsoon thunderstorms, especially in localized urban and rural areas.
“This year, however, we have a very real concern that is different from past years,” Marvin Percha, meteorologist at the National Weather Service in Phoenix, told CNN. “Due to all the fires that have caused burn scars and a loss of vegetation, we have a chance for even greater runoff and even more intense localized flash flooding.”

“Wildland fires remove vegetation and harden the soil, preventing water from infiltrating the ground. Heavy rain over burn scars can lead to flash floods and debris flows,” acting Arizona state climatologist Erinanne Saffell told CNN weather.

That is an immediate concern. The larger concern is the drought situation. Many see the monsoon rains as a reprieve and maybe an end to the drought. But the reality is that Arizona is in a 26-year-old drought.

It will take more than a rain shower to ease drought

Rainfall in any form will provide some drought relief, according to the United States Geological Survey.

“Summer rain can bring small improvements to drought by helping recharge soil moisture and assist forests and pasturelands,” Saffell said.

Summer precipitation can help temporarily alleviate some of those soil and vegetation impacts — like when a person takes medicine for a cold.

“A single dose of medicine can alleviate symptoms of illness, but it usually takes a sustained program of medication to cure an illness,” the USGS writes. “Likewise, a single rainstorm will not break the drought, but it may provide temporary relief.”

In Arizona, the are two rainy seasons — winter and summer.

“Winter precipitation better helps to diminish drought by recharging reservoirs and aquifers, which are the main water supplies in Arizona,” said Saffell.

“Even a good monsoon will not alleviate much the large shortfalls in reservoir storage here in the Colorado River Basin, as stream flow is mostly dependent on winter snow pack in the upper portion of the basin,” Christopher Castro, professor of Hydrology and Atmospheric Sciences at the University of Arizona previously told CNN.

“Drought is a long-term situation, and it usually takes several wetter years to emerge from drought,” Saffell said.
The good news?

“Monsoon rains help to reduce fire season and green up vegetation to help in fire reduction,” Percha said.

So, there is hope, but it will take a lot more medicine to get well from this drought.

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CNN meteorologist Robert Shackelford contributed to this report