Battle to protect sequoias

Fire crews are clearing brush and setting sprinklers to protect two groves of giant sequoias in Yosemite National Park from the Rim fire. Photo / AP

Yosemite staff taking precautions for iconic trees as bushfire rages on park's edge.

A huge bushfire raging on the western boundary of Yosemite National Park has led California's Governor, Jerry Brown, to declare a state of emergency 240km away in San Francisco. Officials fear the blaze could threaten the city's water and power supply.

The week-long blaze on the slopes of the western Sierra Nevada mountains is burning across 523 sq km, threatens 5000 homes and could push deeper into Yosemite - one of the country's most treasured national parks. The so-called Rim fire is one of 50 big blazes currently affecting the western states.It has destroyed four homes and 12 outbuildings and was only 7 per cent contained.

Fire crews are clearing brush and setting sprinklers to protect two groves of giant sequoias. The iconic trees can resist fire, but dry conditions and heavy brush are forcing park officials to take extra precautions in the Tuolumne and Merced groves. About three dozen of the giant trees are affected.

With more than 2600 firefighters struggling to contain the blaze, Brown said the fire had caused damage to electrical infrastructure serving San Francisco's 2.6 million residents. The city receives 85 per cent of its water from the Yosemite area. The blaze is less than 6.5km from the main reservoir, and two of the three hydroelectric power stations in the vicinity have been forced to shut down. The city has so far been able to buy power, but further disruptions or damage could have an effect.

Across the western states, the unusually early and intense fire season has prompted fire and land management agencies to open talks with Pentagon commanders and Canadian officials about bringing in reinforcements. The US forest service reports that more than 31,900 fires have hit 1.2 million hectares this year. Last week, the service said it had spent nearly US$1 billion this year with only US$50 million remaining to control at least 40 fires.

Some experts say a decade-long drought in the western states, along with increased human settlement and activity in fire-prone regions, is behind the increasing severity and frequency of bushfires during the summer season. Almost 87 per cent of the western US is in a drought. Nevada is removing wild horses and stocks of cattle from federal lands, Wyoming is seeding clouds as part of a long-term "weather modification programme". Officials in Colorado say the state's south-eastern plains are experiencing dust-bowl conditions. All of New Mexico is officially in a drought, with ecologists warning of a permanent shift toward a desert ecology. The once-mighty Rio Grande is so dry it is being referred to as the "Rio Sand".

- Observer