The flooding, driven in part by an El Niño pattern, sent torrents of water through normally dry creeks, forced hundreds of evacuations, and cut off access to some communities. But much of that water is now flowing into depleted lakes and underground water stores, according to climate scientist Martin Hoerling of the University of Colorado, Boulder.

“That’s somewhat of an unexpected boost from Mother Nature,” Hoerling said.

Lake Powell, the nation’s second-largest reservoir, has risen more than 20 feet from its mid-September low — a gain that dwarfs what it received from this year’s snowmelt, Hoerling said. The lake, which straddles the Arizona-Utah border, could ultimately see a total increase of over 1.2 million acre-feet, enough water to support roughly 4 million average families for a year.

Still, Lake Powell remains just over a quarter full, and 15 of its 17 boat launches were unusable as of Friday. Last winter’s lackluster snowfall provided little recharge when it melted in spring and summer, leaving reservoirs at record lows.

Local water supplies have also benefited. In Pagosa Springs, Colorado, storms dumped about 7 inches of rain in October, prompting the town to lift water restrictions that had affected more than 10,000 residents. Restaurants had been asked to serve water only on request.

“While the storm was destructive, I think there is a silver lining,” said town manager David Harris. “You’re getting a good start to the winter snowpack in the higher elevations.”

In northern Arizona, Upper Lake Mary — which supplies Flagstaff with up to 40% of its water — has received more than 3 billion gallons since early October. Flagstaff water production manager Brian Huntzinger said last weekend’s storms delivered the equivalent of more than two years of water into the town’s surface supply, providing a buffer for a system that relies heavily on groundwater.

“It’s just a great, great thing to see,” Huntzinger said. “We might be overflowing at this rate before we see any snow fly.”

In central Arizona, floodwaters that trapped people in their homes gushed into streams feeding the Verde River, prompting water officials to release water from two nearly full dams into the river’s normally dry stretch in metro Phoenix, said Bo Svoma, principal meteorologist at the Salt River Project.

Despite the deluge, the region remains in drought, and federal water managers are unlikely to alter Colorado River releases until snowpack peaks next spring, typically around April, according to Jack Schmidt, a professor at Utah State University who studies the river.

Reclamation spokesperson Mary Carlson acknowledged improved conditions but said “considerable uncertainty remains.”

Under a federal plan for the river’s Lower Basin, California, Nevada and Arizona will collectively cut water use by 1.25 million acre-feet annually over the next two years — enough to fill more than 600,000 Olympic-sized swimming pools — with deeper cuts possible if conditions worsen. Nevada and Arizona are challenging the plan in court.

Some Arizona cities have agreed to fund preliminary work on expanding an existing dam on the Verde River to capture storm runoff, Svoma said.

“We need to figure out how to be resilient in a drier future. And we’re not quite there yet,” Hoerling said.