HAZARD IDENTIFICATION

Transcription

1 6.5.8 Wildfire Hazard Identification Description of the Wildfire Hazard A wildfire is any fire occurring in a wildland area (i.e., grassland, forest, brush land) except for fire under prescription. 1 Wildfires are part of the natural management of the Earth s ecosystems, but may also be caused by natural or human factors. Over 80% of forest fires are started by negligent human behavior such as smoking in wooded areas or improperly extinguishing campfires. The second most common cause for wildfire is lightning. There are three classes of wildland fires: surface fire, ground fire, and crown fire. A surface fire is the most common of these three classes and burns along the floor of a forest, moving slowly and killing or damaging trees. A ground fire (muck fire) is usually started by lightning or human carelessness and burns on or below the forest floor. Crown fires spread rapidly by wind and move quickly by jumping along the tops of trees. Wildland fires are usually signaled by dense smoke that fills the area for miles around. State and local governments can impose fire safety regulations on home sites and developments to help curb wildfire. Land treatment measures such as fire access roads, water storage, helipads, safety zones, buffers, firebreaks, fuel breaks, and fuel management can be designed as part of an overall fire defense system to aid in fire control. Fuel management, prescribed burning, and cooperative land management planning can also be encouraged to reduce fire hazards. Severity of the Wildfire Hazard According to the National Fire Plan (2000), the wildland fire risk is considered the most significant fire service problem of the Century. Fire Danger is a description of the combination of both constant and variable factors that affect the initiation, spread, and difficulty to control a wildfire on an area. Since 1974, the National Park Service has used five Adjective Fire Danger ratings to describe danger levels in public information releases and fire prevention signing. Table describes these ratings. 1 Prescription burning, or controlled burn, undertaken by land management agencies is the process of igniting fires under selected conditions, in accordance with strict parameters. A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 139

2 Table Fire Danger Rating System Rating Class 1: Low Danger (L) Color Code: Green CLASS 2: Moderate Danger (M) Color Code: Blue Class 3: High Danger (H) Color Code: Yellow Class 4: Very High Danger (VH) Color Code: Orange Class 5: Extreme (E) Color Code: Red Source: National Park Service Basic Description Fires not easily started Fires start easily and spread at a moderate rate Fires start easily and spread at a rapid rate Fires start very easily and spread at a very fast rate Fire situation is explosive and can result in extensive property damage Detailed Description Fuels do not ignite readily from small firebrands. Fires in open or cured grassland may burn freely a few hours after rain, but wood fires spread slowly by creeping or smoldering and burn in irregular fingers. There is little danger of spotting. Fires can start from most accidental causes. Fires in open cured grassland will burn briskly and spread rapidly on windy days. Woods fires spread slowly to moderately fast. The average fire is of moderate intensity, although heavy concentrations of fuel especially draped fuel may burn hot. Shortdistance spotting may occur, but is not persistent. Fires are not likely to become serious and control is relatively easy. All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and shortdistance spotting is common. High intensity burning may develop on slopes or in concentrations of fine fuel. Fires may become serious and their control difficult, unless they are hit hard and fast while small. Fires start easily from all causes and immediately after ignition, spread rapidly and increase quickly in intensity. Spot fires are a constant danger. Fires burning in light fuels may quickly develop highintensity characteristics such as long-distance spotting and fire whirlwinds, when they burn into heavier fuels. Direct attack at the head of such fires is rarely possible after they have been burning more than a few minutes. Fires under extreme conditions start quickly, spread furiously and burn intensely. All fires are potentially serious. Development into high-intensity burning will usually be faster and occur from smaller fires than in the Very High Danger class (4). Direct attack is rarely possible and may be dangerous, except immediately after ignition. Fires that develop headway in heavy slash or in conifer stands may be unmanageable while the extreme burning condition lasts. Under these conditions, the only effective and safe control action is on the flanks, until the weather changes or the fuel supply lessens. While the planning area could experience the entire range of the hazard, the most common experience expected by the participants would be described as Green (Low Danger) or Blue (Moderate Danger) on the scale above. A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 140

3 Impact to People and Property from the Wildfire Hazard Many individual homes and cabins, subdivisions, resorts, recreational areas, organizational camps, businesses, and industries are located within high fire hazard areas. The increasing demand for outdoor recreation places more people in wildlands during holidays, weekends, and vacation periods. Unfortunately, wildland residents and visitors are rarely educated or prepared for the inferno that can sweep through the brush and timber and destroy property in minutes. Occurrences of the Wildfire Hazard All participants reported experiencing the wildfire hazard. The incidents of wildfire that were reported were described as grass fires ; no participants reported keeping specific records of the incidents, outside of what the fire department or Texas Forest Service would normally maintain for fire incidents. All participants indicated that they felt that it was only a matter of time before a wildfire negatively impacted either people or property. In April 2010, the USDA issued a Disaster Declaration for Drought, Above Normal Temperatures, and Associated Wildfires. This declaration included Atascosa, Frio and Gillespie counties. In January 2006, FEMA issued DR-1624 for Extreme Wildfire Threat. This declaration covered all counties in the state of Texas, including all counties in the planning area. Probability of Future Occurrences of the Wildfire Hazard Fire probability depends on local weather conditions, outdoor activities such as camping, debris burning, and construction, and the degree of public cooperation with fire prevention measures. Drought conditions and other natural disasters (tornadoes, hurricanes, etc.) increase the probability of wildfires by producing fuel in both urban and rural settings. Forest damage from hurricanes and tornadoes may block interior access roads and fire breaks, pull down overhead power lines, or damage pavement and underground utilities. Based on the frequent history of wildfires, the probability of a future occurrence of the wildfire hazard is high. Location and Extent of the Wildfire Hazard The following pages contain two different maps for each participating county (where data exists). The first is the location of reported wildland fires, occurring between (the years of the best available data). The second map illustrates the Wildland Urban Interface (WUI). A WUI refers to the zone of transition between unoccupied land and human development. Communities that are within 0.5 miles of the zone may also be included. These lands and communities adjacent to and surrounded by wildlands are at risk of wildfires. Parameters for the WUI are provided by the Forest and Wildlife Ecology Department, at the University of Wisconsin Madison. For these maps, the following definitions apply: A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 141

4 Low Density Interface: Areas with housing density >= housing units / km² and < housing units / km²; and vegetation <= 50%, within 2.414km of an area with >= 75% vegetation. Medium Density Interface: Areas with housing density >= housing units / km² and < housing units / km²; and vegetation <= 50%, within 2.414km of an area with >= 75% vegetation. High Density Interface: Areas with housing density >= housing units / km²; and vegetation <= 50%, within 2.414km of an area with >= 75% vegetation. Low Density Intermix: Areas with housing density >= and < ; and vegetation > 50%. Medium Density Intermix: Areas with housing density >= and < ; and vegetation > 50%. High Density Intermix: Areas with housing density >= ; and vegetation > 50%. Note that no WUI data was available for Wilson County. A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 142

5 Map Wildland Fire Ignition Locations Atascosa County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 143

6 Map Wildland-Urban Interface Atascosa County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 144

7 Map Wildland Fire Ignition Locations Bandera County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 145

8 Map Wildland-Urban Interface Bandera County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 146

9 Map Wildland Fire Ignition Locations Bexar County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 147

10 Map Wildland-Urban Interface Bexar County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 148

11 Map Wildland Fire Ignition Locations Comal County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 149

12 Map Wildland-Urban Interface Comal County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 150

13 Map Wildland Fire Ignition Locations Frio County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 151

14 Map Wildland-Urban Interface Frio County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 152

15 Map Wildland Fire Ignition Locations Gillespie County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 153

16 Map Wildland-Urban Interface Gillespie County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 154

17 Map Wildland Fire Ignition Locations Guadalupe County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 155

18 Map Wildland-Urban Interface Guadalupe County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 156

19 Map Wildland Fire Ignition Locations Karnes County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 157

20 Map Wildland-Urban Interface Karnes County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 158

21 Map Wildland Fire Ignition Locations Kerr County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 159

22 Map Wildland-Urban Interface Kerr County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 160

23 Map Wildland Fire Ignition Locations Medina County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 161

24 Map Wildland-Urban Interface Medina County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 162

25 Map Wildland Fire Ignition Locations Wilson County A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 163

26 Risk Assessment This subsection of the Plan Updates provides estimates of future wildfire losses, i.e. risk. Each of the loss calculations is based on best available data, but they must be considered estimates because highly detailed engineering was not performed as part of this planning process. Methodology and Limitations After discussion and review of the best available data regarding this hazard, and in consideration of the potential impacts of this hazard to the planning area, the EMC determined that the risk assessment should include both qualitative and quantitative analyses, to the extent possible. Qualitative Each participating jurisdiction was asked to provide a qualitative risk assessment ranking regarding the wildfire hazard. (For definitions of these rankings, please see Table 6.4-1, earlier in this section.) The results of this assessment are presented in the table below Qualitative Risk Assessment Results Wildfire Jurisdictions Ranking Hazard as Low Jurisdictions Ranking Hazard as Moderate Jurisdictions Ranking Hazard as High City of Alamo Heights City of Balcones Heights City of Kirby City of Live Oak City of Terrell Hills City of Windcrest City of Fredericksburg Karnes County City of Kenedy Wilson County City of La Vernia City of Stockdale San Antonio River Authority City of Converse City of San Antonio City of Selma City of St. Hedwig City of Universal City Frio County City of Dilley City of Pearsall Gillespie County Kerr County City of Kerrville Medina County City of Castroville City of Devine City of Hondo City of Natalia Atascosa County City of Charlotte City of Christine City of Jourdanton City of Lytle City of Pleasanton City of Poteet Bandera County City of Bandera Bexar County City of Helotes City of Leon Valley City of Somerset Comal County City of Garden Ridge City of Bulverde City of New Braunfels Guadalupe County City of New Berlin City of Schertz City of Seguin City of Karnes City of Runge City of Falls City City of Ingram A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 164

27 Quantitative Each participating jurisdiction provided information regarding the location and type of critical facilities within their planning area. These facilities were mapped in relation to the High Density Intermix Area. Given the lack of building specific data (only location and use type were available at this time), this analysis assumes that all facilities and mobile homes located within the High Density Intermix are potentially at risk from wildfire. Table lists the facilities at risk by jurisdiction Quantitative Risk Assessment Results Wildfire Jurisdiction Atascosa Bandera Bexar Comal Guadalupe Facilities within High Density Intermix 3 Mobile Homes 3 Mobile Homes 1 Fire Department 16 Mobile Homes 3 Nursing Homes 1 Hospital 2 Schools 22 Mobile Homes 16 Mobile Homes 1 - School Data to collect in order to improve this methodology prior to the Plan Update includes: Data regarding building construction (materials, protection systems, etc.) Data regarding surrounding vegetation Risk Assessment Conclusions Very few critical facilities fall into the High Density Intermix area. However, there are several mobile homes which are located within that area. Jurisdictions should consider working with the inhabitant to insure that they are prepared in the event of a wildfire and have taken steps to protect their property. A S A F E, S E C U R E, A N D S U S T A I N A B L E F U T U R E SECTION 6: PAGE 165