Here are the impacts of extreme heat and record high temperatures across the US West

Californians brace for rolling blackouts

Residents of the Golden State have been told to prepare for the possibility of power outages as record demand threatens to outstrip the power supply while heat records are broken across the state.

Forecasted demand “is at all-time record levels and the potential for rotating outages has increased significantly,” said Elliot Mainzer of the California Independent Systems Operator.

The state saw record temperatures Monday, including in Sacramento, which hit 114 degrees Fahrenheit, making it the city’s hottest September day on record. San Francisco International Airport hit 97 degrees, a daily record, and that city remains under a heat advisory Tuesday.

Further south, Death Valley could hit 125 degrees Tuesday, which would tie its hottest September temperature on record. (Despite an unofficial reading of an even higher temperature, Death Valley on Friday officially only reached 124 degrees. And its September record is still short of Earth’s all-time record for the month: 126 degrees, set in 1950 in Mecca, California.)

If rotating outages occur this week in California, they would likely last at least 40 minutes each before power is restored for the first set of impacted customers and goes out for the next group. Utilities would try to keep outages as short as possible, Mainzer assured customers, but operators anticipate power supply deficits between 400 and 3,400 megawatts between 5 p.m. and 9 p.m. Tuesday.

Fish died in a Utah reservoir

And California’s regional neighbors are toying with record high temperatures, too. Billings, Montana, also hit 100 degrees on Monday, the first time the city has hit 100 degrees twice in the same September.

In fact, temperatures have been so high in Utah this summer that wildlife biologists have attributed the heat and low water levels to the deaths of fish late last month: Roughly 80 kokanee salmon were confirmed dead on August 26 at Lost Creek Reservoir, about 70 miles northeast of Salt Lake City, according to Faith Jolley, a spokesperson for the Utah Division of Wildlife Resources, though she noted that was “quite a small amount of the total fish there.”

Still, with “the recent heat wave and record number of hot days this summer and lower water levels, water temperatures at Lost Creek are just starting to reach the thermal maximum for what kokanee can tolerate,” Jolley said in an email.

Water levels in lakes and reservoirs fall during a drought, she explained, and at a lower water level, those bodies of water heat more quickly. That’s bad for fish, Jolley said, because warm water holds less oxygen than cooler water. Together, the high temperatures and lack of oxygen can result in poor fish growth, disease and even death.

Wildfires kill 4 in California

Fire officials have yet to identify those who died in the fire or the circumstances in which they perished.

Prolonged drought has left behind a “huge amount of dead fuel,” Cal Fire Battalion Chief Jon Heggie told CNN Sunday, calling the conditions “extremely dangerous.”

“All these fires now have receptive fuel beds to burn,” he said. “Now, when anything gets started, it has that potential for exponential growth in a short period of time just because everything is so tinder dry.”

Arizona hiker dies, five others injured

Tragically, one of the hikers, a man in his 20s, was pronounced dead after being taken to a hospital, a spokesperson for the Maricopa County Sheriff’s Office said. Five others were treated at the Spur Cross Trailhead.