TECHNICAL BACKGROUND REPORT to the 2003 SAFETY ELEMENT CITY of GLENDALE, CALIFORNIA CHAPTER 4: FIRE HAZARDS 4.1 Wildland Fires Due to its weather, topography and native vegetation, the entire southern California area is at risk from wildland fires. The extended droughts characteristic of California’s Mediterranean climate result in large areas of dry vegetation that provide fuel for wildland fires. Furthermore, the native vegetation typically has a high oil content that makes it highly flammable. The area is also intermittently impacted by Santa Ana (or Santana) winds, the hot, dry winds that blow across southern California in the spring and late fall. These winds often fan and help spread fires in the region. Combine these conditions with the fact that more people than ever are living and playing in wildland areas, and the potential for major wildland fires to occur increases even further. In fact, the wildfire risk in the United States has increased in the last few decades with the increasing encroachment of residences and other structures into the wildland environment and the enduring drought conditions that have affected some regions. Between 1990 and 1999 inclusive, there were on average 106,347 wildfires annually in the United States, for a combined average annual burn of nearly 3.65 million acres of brush (htpp://nifc.gov/fireinfo/1999/highlites.html). These fires are for the most part caused by people: between 1988 and 1997, human-induced fires burned nearly eight times more acreage than fires caused by lightning. A wildfire that consumes hundreds to thousands of acres of vegetated property can overwhelm local emergency response resources. Under the right wind conditions, multiple ignitions can develop as a result of the wind transport of burning cinders (called brands) over distances of a mile or more. Wildfires in those areas where the wildland approaches or interfaces with the urban environment (referred to as the urban-wildland interface or UWI) can be particularly dangerous and complex, posing a severe threat to public and firefighter safety, and causing devastating losses of life and property. This is because when a wildland fire encroaches onto the built environment, ignited structures can then sustain and transmit the fire from one building to the next. This is what happened at three of the most devastating fires in California: the Oakland Hills/Berkeley Tunnel fire of October 1991, the Laguna fire of 1970 in northern San Diego County, and the Laguna Beach fire of 1993. In the Oakland Hills fire, 25 lives were lost, and 2,900 structures were damaged for a total of $1.7 billion in insured losses. The September 1970 fire, which started as a result of downed power lines, burned 175,425 acres, destroyed 382 structures and killed 5 people. The Laguna Beach fire of 1993 burned 14,437 acres and destroyed 441 homes, but thankfully no lives were lost. It is clear that continuous planning, preparedness, and education are required to reduce the fire hazard potential, and to limit the destruction caused by wildfires. Fires usually last only a few hours or days, but their effects can last much longer, especially in the case of intense fires that develop in areas where large amounts of dry, combustible vegetation have been allowed to accumulate. If wildland fires are followed by a period of intense rainfall, debris flows off the recently burned hillsides can develop. Flood control facilities may be severely taxed by the increased flow from the denuded hillsides and the resulting debris that washes down. If the flood control structures are overwhelmed, widespread damage can ensue in areas down gradient from these failed structures. This happened in several communities in and near the base of the San Gabriel Mountains during the winters of 1934, 1969, 1978, and 1980, with areas below burned watersheds receiving the bulk of the damage. In November 1933, there was a large fire in the Montrose-La Crescenta area that burned more than 5,000 acres. Then, on January 1, 1934, the recently burned watershed experienced an exceptionally intense rainstorm. Debris-laden flows that overtopped canyons impacted the La Crescenta and Glendale areas. Streets were clogged with debris, several bridges were washed out, and several people died (see Chapters 2 and 3). Earth Consultants International Fire Hazards Page 4-1 TECHNICAL BACKGROUND REPORT to the 2003 SAFETY ELEMENT CITY of GLENDALE, CALIFORNIA However, this does not need to happen if remedial measures following a wildfire are taken in anticipation of the next winter. Studies (Cannon, 2001) suggest that in addition to rainfall and slope steepness, other factors that contribute to the formation of post-fire debris flows include the underlying rock type, the shape of the drainage basin, and the presence or absence of water-repellant soils (during a fire, the organic material in the soil may be burned away or decompose into water-repellent substances that prevents water from percolating into the soil.) Other effects of wildfires are economical and social. Homeowners who lose their house to a wildfire may not be able to recover financially and emotionally for years to come. Recreational areas that have been affected may be forced to close or operate at a reduced scale. In addition, the buildings that are destroyed by fire are usually eligible for re-assessment, which reduces income to local governments from property taxes. The impact of wildland fire on plant communities is generally beneficial, although it often takes time for plant communities to re-establish themselves. If a grassland area has been burned, it will re-sprout the following spring. A chaparral community, however, takes three to five years to recover. Oak woodland, which has had most of the seedlings and saplings destroyed by fire, will require at least five to ten years for a new crop to start. Regardless of the comments above, we should not forget that wildland fire is a natural process. In the past, the presumption has been that all wildfire is bad, and that it should therefore be extinguished promptly. This has caused fire-dependent plant communities to grow more densely, which ultimately weakens the plants in their struggle for living space and increases their destruction by pests and disease. Dead and dying plants add fuel for fire. In addition, the absence of fire has altered or disrupted the cycle of natural plant succession and wildlife habitat in many areas (http://www.nps.gov/gosp/resource/fire_nps.htm). Consequently, land management agencies are now committed to finding ways, such as prescribed burning, to reintroduce fire into natural ecosystems. Future efforts to reduce this hazard need to consider ways of managing wildland fire to benefit the natural environment, while reducing the potential for structural fires in the built environment. Policies developed to manage the fire hazard will be successful if a balance between both goals is obtained. 4.1.1 Wildland Fire Susceptibility Mapping Wildfires have been part of the natural ecosystem in the rolling hillsides and mountains of southern California for thousands of years. Some of the plants native to this area actually require periodic burning to germinate and recycle nutrients that enrich the soils. Researchers have also determined that Native Americans in California used fire to reduce fuel load and improve their ability to hunt and forage. It is thought that as much as 12 percent of the State was burned every year by the various tribes (Coleman, 1994). In the early 20th Century, as development started to encroach onto the foothills, wildfires came to be unacceptable as they posed a hazard with the potential loss of property and even life. As a result, in the early 1920s, the fire service began to prevent wildfires from occurring. Unfortunately, over time, this led to an increase in fuel loads. Wildfires that impact areas with fuel buildup are more intense and significantly more damaging to the ecosystem than periodic, low-intensity fires. The fire hazard of an area is typically based on the combined input of several parameters. Some of these conditions include: • fuel loading (that is, type of vegetation, its density, and moisture content), • topography (slope), Earth Consultants International Fire Hazards Page 4-2 TECHNICAL BACKGROUND REPORT to the 2003 SAFETY ELEMENT CITY of GLENDALE, CALIFORNIA • weather, • dwelling density and accessibility, • building construction (with emphasis on combustible roof coverings), • wildfire history, and • whether or not there are local mitigation measures in place that help reduce the zone’s fire rating (such as an extensive network of fire hydrants, fire-rated construction materials, fuel modification zones, fire sprinklers in structures, etc.). Since the early 1970s, several fire hazard assessment systems have been developed for the purpose of quantifying the severity of the hazard in a given area. Those that have been developed in California are described further below. Early systems characterized the fire hazard of an area based on a weighted factor that typically considered fuel, weather and topography. More recent systems rely on the use of Geographic Information System (GIS) technology to integrate the factors listed above to map the hazards, and to predict fire behavior and the impact on watersheds. HUD Study System: In April 1973, the California Department of Forestry and Fire Prevention (CDF) published a study funded by the Department of Housing and Urban Development (HUD) under an agreement with the Governor’s Office of Planning and Research (Helm et al., 1973). As is often the case, the study was conducted in response to a disaster: during September and October 1970, 773 wildfires burned more than 580,000 acres of California land. The HUD mapping process relied on information obtained from US Geological Survey (USGS) 15- and 7.5-minute quadrangle maps on fuel loading (vegetation type and density) and slope, and combined it with fire weather information to determine the Fire Hazard Severity of an area.