In order for the spread of the 117,000-acre Caldor Fire to stop or to be suppressed by firefighters, something will have to change — either the weather or the fuel.
If the relative humidity stayed above 40 percent and the wind speed was less than five mph, it might lose enough intensity to allow firefighters on the ground and in the air to take direct action on the flanks. But there is no sign of that happening this week.
To see all articles on Wildfire Today about the Caldor Fire, including the most recent, click HERE.
Let’s look at the fuel, which is the primary driver of this fire.
From the Incident Management Team:.
There is a heavy dead and down component with drought-stressed fuels. Live fuels are cured to levels normally seen in late September, and fuels are extremely receptive to spotting. Fuel moistures are historically low. Northern California remains under a Fuels and Fire Behavior Advisory. ERC’s are above the 97th percentile. 100 hr and 1000hr fuels are below [3 percent fuel moisture].
The predominant direction of spread has been to the northeast or east-northeast. If it continues in that direction for the next 10 miles it will not encounter the footprints of any fires that have burned in the last 21 years large enough to have a significant effect on the spread. Just beyond that distance on the north side of Highway 50 is the 2007 Angora Fire southwest of South Lake Tahoe.
North of Highway 50 four miles northeast of the location of the fire Monday night there is a large rocky area several miles across with sparse fuel. It is north of Twin Bridges and west of Fallen Leaf and could slow the fire in that location, but there’s no guarantee that it can’t find a way to burn around, through, or over it. Spot fires have been igniting a mile out in front; one was 1.8 miles.
Another fuel-related factor to consider is the fuel treatments that have been accomplished over the years, shown in green on the map above. The Caldor Fire has already burned across dozens, and it will be interesting to find out if they had the intended effect. There has been a great deal of fuels work in the South Lake Tahoe area.
A reduction in the volume of vegetation resulting from a fuels project in most cases is not expected to stop a high-intensity wildland fire. At best in those areas the fire may spread more slowly and perhaps throw out fewer burning embers.
But by far the best protection for structures is make them as fire resistant as possible, including the envelope of the structure itself — the roof, vents, siding, doors, windows, foundation, fences, eaves, and decks. A FEMA publication (13 MB) has excellent detailed recommendations. And in the Home Ignition Zone the NFPA and FireWise programs recommend reducing flammable material within 100 feet of structures and spacing the crowns of trees at least 18 feet apart that are within 30 feet of the home, 12 feet apart at 30 to 60 feet, and 6 feet apart at 60 to 100 feet. Another house that is 15 to 50 feet away is also fuel, and if it ignites will be a serious threat.
The LA Times (subscription) published an excellent article August 21 about rethinking forest management — the effects of logging and prescribed fire, and learning to live with fire.