El Niño floods recharge Southwest reservoirs from record lows

Lake Powell has risen more than 20 feet since mid-September

Lake Powell, the second-largest reservoir in the U.S., rose more than 20 feet (6.1 meters) from its mid-September low — a gain that dwarfed this year’s snowmelt, climate scientist and hydrologist Martin Hoerling said. Still, the lake remained just over a quarter full, and 15 of its 17 boat launches remained unusable as of Friday. Hoerling estimated that floodwaters and additional rain could raise the lake along the Arizona-Utah border further, for a total gain of more than 1.2 million acre-feet — enough to support around 4 million average families for a year.

Storms in late October and early November sent torrents of water through normally small or dry creeks that overflowed their banks and flooded local communities across the Southwest. Hundreds of people were told to evacuate, and the flooding cut off access to some areas. Martin Hoerling, a climate scientist and hydrologist at the University of Colorado, Boulder, said most of that water will end up feeding depleted lakes and underground aquifers. “That’s somewhat of an unexpected boost from Mother Nature,” Hoerling said.

The rise followed a year in which lackluster winter snowfall did little to recharge water bodies when it melted in the spring and summer, the period when reservoirs typically get their biggest bump of the year. Then came El Niño, which has intensified heavy rain and floods. Experts said El Niño’s impacts will last several more months, potentially further boosting water supplies across the West, where water is primarily stored in lakes, aquifers and snowpack.

Rain has brought temporary relief to regional and local water supplies. Cities in the region reported some of their wettest weather in decades.

Before storms began dumping about 7 inches (17.78 centimeters) of rain around Pagosa Springs, Colorado, in October, more than 10,000 people in the town and surrounding communities were under water restrictions. Restaurants were encouraged to serve water only on request, town manager David Harris said. Those restrictions have now been lifted.

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

Upper Lake Mary, which captures spring snowmelt in Northern Arizona and supplies Flagstaff, Arizona, with up to 40% of its water, received more than 3 billion gallons of water since early October, said Flagstaff water production manager Brian Huntzinger. Storms last weekend dumped the equivalent of more than two years of water into the town’s surface water supply and provided a buffer for an operation that depends heavily on underground aquifers, Huntzinger said.

“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, heavy floodwaters that trapped people in their homes gushed into streams that feed the Verde River. That prompted water officials to release water from two nearly full dams into the Verde’s normally dry stretch in metro Phoenix, said Bo Svoma, the principal meteorologist at the Salt River Project, which manages reservoirs on the Salt and Verde rivers.

The region remains in drought despite the intense rains, and wet weather is unlikely to change decisions on the Colorado River. Allocation decisions have already been made for the basin. Jack Schmidt, a Utah State University professor who studies the Colorado River, said the U.S. Bureau of Reclamation, which manages reservoirs in the West, is unlikely to change its water releases from Lake Powell or other areas until it knows when snowpack has peaked, typically around April.

Under the federal plan for managing the Colorado River’s Lower Basin, California, Nevada and Arizona will collectively reduce water use by 1.25 million acre-feet (about 1.54 billion cubic meters) annually in the next two years. That is enough to fill more than 600,000 Olympic-sized swimming pools, with the possibility of larger cuts depending on conditions. Nevada and Arizona are challenging the plan in court.

Some Arizona cities have agreed to fund preliminary work aimed at reducing reliance on the Colorado River by expanding an existing dam on the Verde River to capture runoff from storms, Svoma said. Bureau of Reclamation spokesperson Mary Carlson acknowledged that conditions had improved but said, “considerable uncertainty remains.” Hoerling said, “We need to figure out how to be resilient in a drier future. And we’re not quite there yet.”