The torrent of rain that turned a Grand Canyon creek into a raging river in less than an hour on Saturday was fueled in part by moisture that had been transported from as far away as the Pacific Ocean.
It arrived over Arizona as part of the annual monsoon season, which often leads to heavy rain in the Grand Canyon and across the West each summer. During the season, the region’s prevailing winds shift from the west to the south, bringing moisture to desert areas of the southwest that are more typically very dry. Its effects are usually strongest in Arizona and New Mexico, but the moisture can spread as far north as Colorado and Northern California.
At least two people died on Saturday as the surge of water swept through Bright Angel Canyon, where a cluster of historic stone cabins known as Phantom Ranch sits along a creek that quickly swelled.
“The rain just happened to fall over the wrong place,” said Justin Johndrow, a meteorologist with the National Weather Service office in Flagstaff, Ariz. “It happened to fall over a very sensitive area.”
On Saturday, heavy and fast-moving thunderstorms passed over Bright Angel Canyon and dumped just over an inch of rain in 30 minutes, from about 2:30 p.m. to 3 p.m.
The actual amount of rain was not high, meteorologists said, but it came down at an unusually fast rate. It landed in sheets over a rocky, impermeable landscape and gained speed as it moved 5,500 feet from the top of the canyon to the bottom.
“The water accelerated a lot faster than it would on a flatter surface,” Mr. Johndrow said.
The rush of water tore apart footbridges spanning the creek and wiped out trails.
The flooding occurred as the El Niño weather pattern is strengthening, and officials have warned that the phenomenon could help lead to more extreme weather in the coming months, particularly in winter when its affects are typically strongest.
But experts said it would be tricky to directly connect the very localized storms that occurred on Saturday to the large-scale pattern that affects weather patterns around the world.
While El Niño affects where moisture collects in the atmosphere, “‘fingerprinting’ any direct influence of a rapidly developing El Niño on that weather event is far from trivial,” said Kim Wood, an associate professor in the department of hydrology and atmospheric sciences at the University of Arizona.
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