Wet May sets rainfall record, helps irrigation



Little Cottonwood Creek at Wheeler Farm.

After a dry and mild winter, May in Utah was wetter than usual.

“We had a series of upper-level troughs move through the area, and that in itself was the driving force with all the rain we got,” said Brian McInerney, a National Weather Service hydrologist. “The high pressure was dogging us—typically in the spring that goes away. It went away and that opened the door for upper-level troughs to move in that were moisture laden. We had a lot of rain through that entire month, maybe 300% to 400% of normal.”

In Salt Lake City, those rains set a new record. “We had 18 days of measurable rainfall at the airport. That was a record,” said McInerney. “We broke records on the wet side in May; we were breaking heat and dry records in the wintertime. From one extreme to the other.”

MayPrecipAccording to the National Weather Service, the airport received a total of 4.19 inches in May, or 215% of the normal 1.95 inches.

While welcome, the rain does not significantly improve the long-term water outlook through the summer, but it does help in the short term.

“Typically, when you get a cool, wet spring, it enhances the spring runoff and makes it more efficient,” McInerney explained. “But we didn’t really have any runoff to speak of. We were missing the main part: the actual snow accumulation season. … In our area [the rain] improved the volume forecasts by 5% to 7% that we expect as a result of the rains in May. It really wasn’t a big jump. … The actual volume of water coming out of the mountains is still going to be pretty sparse. But where it did help as the fact that people stopped using their sprinklers during May. … It helped in the form of people not using stored water.”

Although the rain may not make much difference for the long-term supply, it makes a big difference for certain water users.

“It does for us,” said Mike Tea, water master with Richards Irrigation Company, which provides secondary water to parts of Sandy and Cottonwood Heights. “We don’t get our water out of storage, we get it out of streamflow.”

“[The rain] has kept Little Cottonwood Creek flowing just real even. It keeps that streamflow up high enough to where it really benefits us. It does us a lot of good,” Tea said. “I find that with rain like that, we get three or four days of good water. … There’s enough [runoff] into our stream to keep it going.”


Robert B. Sowby

Robert B. Sowby is a water resources engineer at Hansen, Allen & Luce. A graduate of BYU, MIT, and the U, he has contributed to over 100 civil, water, and environmental projects throughout North America.

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