A TALE OF TWO ARIZONA FIRES: A CASE STUDY OF THE MUSEUM AND TELEGRAPH FIRES EMERGENCY FLOOD RISK ANALYSES, AND SUBSEQUENT MONSOONAL FLOODING

In July 2021, two AZ communities experienced post-fire flooding: for one, it was the first significant rain since the fire 2 years ago, and for the other, the fire was still burning.

In July 2019, the Museum Fire burned ~2,000 ac. directly north of Flagstaff, AZ. Coconino County, the City of Flagstaff, JE Fuller, Inc., and others worked in coordination to rapidly assess potential flood risks and implement a flood warning system. The day the fire ignited, we began modeling post-fire flood scenarios using 2-dimensional flood modeling software and a design storm based on previous post-fire flooding in the area. We produced a series of flood risk maps, starting with a worst-case scenario of all moderate-high soil burn severity (SBS), and updated the model and maps as the fire grew and mapped SBS data became available. Over 400 structures were identified as needing flood protection and barriers were installed. Then, the community waited through the two driest monsoons on record. Many residents were frustrated, believing that floods would not happen, and some chose to remove barriers. Two years later, in July 2021, the burn area received three rainfall events, resulting in major flooding and damages in unprotected areas. The flood risk maps matched the actual flood extents well and was an effective tool to help the community prepare for flooding.

In June 2021, the Telegraph Fire burned ~180,000 ac. south of Globe, AZ. The fire burnt through the Pinal Mountains, impacting large watersheds that drain directly into the cities of Globe and Miami. We began the same flood risk assessment procedures within days of the fire ignition and provided local agencies with preliminary flood risk maps. Community outreach was conducted to inform residents of the risks and the existing flood warning system was expanded. On July 3, the day of fire containment, the burn scar experienced its first rainfall, resulting in residential flooding. Several additional floods occurred in early July with damages to homes and infrastructure. Though there was not time to implement significant mitigation measures, the flood risk maps reflected the extent of flooding well, and provided valuable data for the community to prepare for floods. These two scenarios illustrate how emergency flood risk assessments can help communities prepare for post-fire flooding.