SOUTH LAKE TAHOE, Calif. — The Caldor Fire burned hottest in decimated communities, and the landscape has dramatically changed on the main highway leading to South Lake Tahoe.
Blackened earth, scorched trees and burned homes are prominent alongside Highway 50, from Echo Summit to Kyburz.
The U.S. Forest Service Burned Area Emergency Response Team recently completed data gathering and analysis of the Caldor Fire-burned area to produce a soil burn severity map of the 219,578-acre, 76% contained blaze.
The map and data display soil burn severity categories: unburned/very low, low, moderate, and high. Approximately half of the acreage of the fire (47%) is either unburned/very low or low, while 40% sustained moderate and about 13% high.
While the fire didn’t burn the hottest on Echo Summit, according to the map, many of the cabins overlooking the basin are no longer there. The fire reduced them to rubble.
Many work crews had chainsaws fired up in the forest beside Highway 50 on Tuesday. The highway was fully reopened at 8 a.m. that day for the first time since Aug. 20, and vehicles shortly afterward started streaming into the basin.
SOIL BURN SEVERITY
The severity map shows the fire burning hottest in the decimated Grizzly Flats community, where hundreds of homes were lost; and along Highway 50, where houses were destroyed on both sides of the highway in Phillips near Sierra-at-Tahoe.
Burned Area Emergency Response Teams are multi-disciplinary teams sent to federal lands following significant wildfires to characterize a fire’s effects to watersheds, identify imminent post-fire threats to human life and safety, property, infrastructure, and critical natural and cultural resources. The team assesses the effects to soils, not vegetation. Soil burn severity characterizes the effects at the soil surface and below ground, whereas vegetation effects are determined based on mortality and vegetation canopy changes.
Once the assessment is done, the team develops emergency treatment recommendations to mitigate identified risks. Teams then implement recommended treatments and action stabilization measures.
These teams begin their assessment immediately after the fire threat passes. They focus on the direct damage caused by the fire, rather than from fire suppression activities. Post-fire conditions such as loss of vegetation and the changes in the soils will increase the likelihood of floods and may cause potential debris and sediment flow impacts.
For complex fires such as the Caldor Fire, assessments are done as an interagency effort that includes a California State Watershed Emergency Response Team. The Cal Fire WERT team is evaluating burned private and state lands from the fire. Both teams share information as they complete their evaluations, analysis and subsequent reports.
Changes in factors like soil cover and biological changes determine the level of soil burn severity. Changes in water repellency is a much-discussed fire effect. Fire can increase the severity and the thickness of the water-repellent soil, which has significant effects on post-fire water runoff.
Low soil burn severity indicates there was only partial consumption of fine fuels while litter coverage remains relatively intact on the soil surface. Burning time at the soil surface was short, leaving root systems and root structure undamaged. Vegetative recovery time in the low category will vary based on ecological community, but is expected to recover in the short term.
Moderate soil burn severity indicates nearly all soil cover of vegetative litter and fine fuels was consumed or converted to ash. Because soil cover is significantly reduced, accelerated water runoff is expected. Charring of the mineral soil occurs in moderate soil burn severity as well as shallow root burning. The extent of the burning of the leaves and needles on the trees can be unpredictable and can range from high to relatively low mortality.
High soil burn severity is the result of higher intensity fire behavior or longer burning time at the soil surface. As a result of the high heat, nearly all the soil cover of vegetative litter and fuels has been consumed, leaving bare soil prone to the impacts of precipitation and resulting water runoff.
“Everyone near and downstream from the burned areas should remain alert and stay updated on weather conditions that may result in heavy rains over the burn scars,” a press release states. “Flash flooding may occur quickly during heavy rain events, be prepared to take action.”
For weather and emergency notifications, visit the National Weather Service website at www.weather.gov/sto.
Bill Rozak is the editor of the Tahoe Daily Tribune, a sister publication of The Union