Background

In late October 2003, wildfires burned approximately 700,000 acres in Southern California. The effects of wildfires on vegetation and soils can cause substantial increases in runoff, significantly increasing the flood hazards in fire-affected watersheds until the burned areas recover, which can often take several years. To assist local, regional and federal agencies in accounting for the increased flood hazards during their recovery and mitigation efforts, FEMA Region IX, in cooperation with the California Office of Emergency Services, has initiated an effort to analyze the post-fire flood hazards for streams in the five counties affected by the fires: San Diego, San Bernardino, Riverside, Los Angeles, and Ventura. The maps resulting from this analysis show the increased flood hazard areas created by the wildfire damage. These maps are intended to assist homeowners, and local, state, and federal agencies in recognizing and dealing with this substantially increased flood risk.

Post-Fire Advisory Flood Hazard Maps

Maps presenting the results of these analyses and related information can be downloaded from this website. These maps show approximate pre-burn and post-burn flood hazard areas for the base flood (the flood that has a 1-percent chance of occurring in a given year). These maps are intended to provide a general understanding of approximate flood risk areas and to identify areas where the flood risk has increased significantly as a result of the fires. The maps do not replace detailed engineering analyses. Additionally, they do not replace the currently effective Flood Insurance Rate Maps for the affected communities, which continue to be the officially adopted maps for insurance purposes. For insurance rating, please refer to the currently effective Flood Insurance Rate Map (FIRM), available from your local government or the FEMA Map Service Center (1-800-358-9616 / http://store.msc.fema.gov).

Study Methods and Data Sources

In order to create and provide these maps in the quickest timeframe possible, FEMA relied on readily available data and approximate analysis methods. Where available, the pre-burn flood hazard areas shown on the maps are based upon flood data generated from FEMA's Flood Insurance Rate Maps. For post-burn conditions and for areas not previously studied under the NFIP, approximate study methods were used. Field reconnaissance was performed to collect general information about structures (e.g., bridges, culverts, etc.); however, detailed survey information of these structures was not collected. Peak discharges were calculated using the U.S. Geological Survey (USGS) regional regression equations, adjusted for post-fire hydrologic conditions (Download table of estimated peak post-fire discharges - 942KB Adobe® PDF file - Download the free Reader). Approximate floodplain elevations were calculated using the HEC-RAS model, developed by the U.S. Army Corps of Engineers. The floodplains were mapped on topographic information obtained from the USGS. For additional information regarding study methods, see the document titled "The Hydrologic and Hydraulic Methodology Used to Estimate Post-Burn Floodplain Hazards" (164KB Adobe® PDF file - Download the free Reader).

Flood Insurance Availability

All of the communities in the areas affected by the wildfires participate in the National Flood Insurance Program (NFIP); therefore, flood insurance can be purchased for any building in these communities no matter what flood zone the building is located in. Flood insurance can also be purchased for building contents. The cost of flood insurance will be based on the "pre-burn" flood zone designations that appear on the current Flood Insurance Rate Maps for these communities. The cost of flood insurance will not be changed in these areas because of the short-term increase (3-5 years) in the flood hazards that are shown on these maps as a result of the wildfires. For questions regarding the purchase of flood insurance, please contact your insurance agent or the NFIP at 1-800-427-4661.