Wildfire threatens San Francisco water supply

A wildfire raging on the edge of the Yosemite National Park threatened both one of America’s premier sites of natural beauty and a reservoir that supplies San Francisco.

The massive blaze, which began 10 days ago, has grown to become the 13th largest in California’s recorded history.

A map posted on InciWeb, an inter-agency fire tracking website, showed the inferno nearing the Hetch Hetchy Reservoir, the main source of fresh water for 2.6m people living in the San Francisco Bay Area, some 320km to the west. Local news media reported flames from the Rim Fire were a mere 8km from the reservoir.

The blaze has scorched 149,780 acres (60,614 hectares) and is just 15% contained, said Cal Fire, the California Department of Forestry and Fire Protection.

Several evacuation orders and advisories are in effect, it said, adding that 4,500 homes remain threatened and thatwindy conditions could complicate efforts to contain the blaze.

Tyrone Jue with the San Francisco Public Utilities Commission told the San Francisco Chronicle that there have been no interruptions in the water supply, and that there has been no change in the quality of drinking water.

The utility said it also had large reserves of water stored locally, which it will make available if the fire interrupts delivery.

However, the city also relies on hydroelectric power from the same region: two of its three power plants were shut down when the fire swept through, Jue told the Chronicle.

The city kept the power flowing by relying on agreements with other utility companies and buying supplemental power.

More than 2,800 firefighters, supported by helicopters and air tankers, are struggling to contain the blaze, which started on Aug 17 from still unknown causes.

Extremely dry conditions due to a prolonged drought, coupled with inaccessible terrain in the affected area, have exacerbated the severity of the incident.

According to satellite photos, giant columns of white smoke were drifting north into the neighbouring state of Nevada.

The Rim Fire “is expected to continue to exhibit very large fire growth due to extremely dry fuels and inaccessible terrain,” Inciweb said.

The fire edged closer to San Francisco’s giant sequoia trees that are among the largest and oldest living things on earth. They can resist fire but were being sprinkled for protection.