The BWARE Definition

There are many different types of natural hazards, from hurricanes to earthquakes. With regard to post-wildfire natural hazards though, we are generally talking about environmental phenomena that have the following criteria:

• are characterized by downslope mobilizations of water, rock, soil, and/or other debris – potentially transporting large volumes of these materials at high velocity

• occurs with little to no warning, most often during or immediately following a rainfall event

• have the potential to cause loss of life, significant property damage, social and economic disruption, and/or environmental degradation

This relatively broad definition captures a range of natural hazards with names you might recognize, like: landslides, debris flows, mudflows, rockfalls, and flash floods. While these types of hazards occur frequently across many regions of the world, to be considered a post-wildfire natural hazard, the events must also have two additional criteria:

• occurs within or immediately downstream of the footprint of a recent wildfire

• would not have been predicted to occur if not for the environmental effects of the fire

The video here is an example of a post-fire natural hazard that occurred in British Columbia, Canada in 2024. Though the foreground may look relatively unburned, the watershed upstream of this location was heavily impacted by a wildfire in the previous year. As a result of these effects, many post-fire natural hazards can be triggered without storms delivering high magnitudes of rainfall. In fact, because of post-fire monitoring conducted by the BWARE team, we know that this specific event occurred following a storm that lasted roughly 10 minutes while delivering less than 1 cm of total rainfall!

There are many approaches to classifying natural hazards.