Wildfire and Geomorphic Events

The rapid increase in the frequency and intensity of wildfire events across the world not only increasingly exposes communities to the risk of being directly harmed by the events of wildfire but also causes many communities to be living under the danger of the secondary hazards of wildfire, such as wildfire associated geomorphic events like landslides and debris flows (Franz, 2021).

In order for us to better manage the risk imposed by the secondary hazards of wildfire events, a better understanding of the relationship between wildfire and the geomorphic events associated therewith is necessary.

In this study, quantitative research was performed to analyze the relationship between the time elapsed since the most recent events of wildfire and the frequency of two types of geomorphic events (landslides, and debris flows). All the data and information utilized in the research are collected from the region of the Rocky and Omineca Mountains in the Canadian province of British Columbia

The process of data derivation could roughly be broken into two parts, the identification of post-wildfire geomorphic events and then used the identified post-wildfire geomorphic events to construct a post-wildfire geomorphic events inventory. 

After the post-wildfire geomorphic events inventory had been constructed, it was converted into a CSV file. In the CSV file, each entry represents one incident of wildfire. Within each entry, two columns of data, one being the year elapsed since the most recent event of wildfire (calculated by subtracting the year of the geomorphic event against the year of the wildfire), and another one being the number of geomorphic events that had happened within the boundary of that wildfire.

Once the construction of the CSV file was done, the data contained therein was used to conduct statistical analysis.

The result has three key findings. First, in general, the frequency of geomorphic events tends to increase drastically after an area has been impacted by an event of a wildfire, but the increased frequency of geomorphic events would gradually decrease as time progresses. Overall, there exists a statistically strong negative temporal correlation between the time elapsed since the most recent event of a wildfire and the frequency of post-wildfire geomorphic events. Second, despite the presence of a statistically strong negative correlation with the frequency of post-wildfire geomorphic events, the time elapsed since the most recent wildfire has very poor explanatory power for predicting the frequency of post-wildfire geomorphic events. Third, slope appears to be an important factor that is influential for the relationship between the frequency of geomorphic events and the time elapsed since the most recent event of a wildfire, as a statistically significant negative correlation between the two variables is only observed when the terrain is at least gently sloped.  

These three findings could be explained by wildfire's impacts on soil hydrophobicity. Immediately after the burning of wildfire, the frequency of wildfire tends to increase rapidly since the burning of wildfire could increase the hydrophobicity of soil and therefore makes the soil more prone to erosion and more suspectable to the happening of geomorphic events like landslides or debris flows (Parise & Cannon, 2011). After the wildfire, soil hydrophobicity would gradually return to the pre-burning state, as a result of that, the frequency of post-wildfire geomorphic events would gradually decrease (Parise & Cannon, 2011). Since the happening of geomorphic events is closely tied to soil erosion and in plain terrain where the effects of soil erosion are weaker than the effects of soil sedimentation regardless of soil hydrophobicity, the role of slope within the relationship between wildfire and the frequency of post-wildfire geomorphic events could also be explained (Parise & Cannon, 2011).