A LiDAR-based analysis of the effects of slope, vegetation density, and ground surface roughness on travel rates for wildland firefighter escape route mapping

Abstract

Escape routes are essential components of wildland firefighter safety, providing pre-defined pathways to a safety zone. Among the many factors that affect travel rates along an escape route, landscape conditions such as slope, low-lying vegetation density, and ground surface roughness are particularly influential, and can be measured using airborne light detection and ranging (LiDAR) data. In order to develop a robust, quantitative understanding of the effects of these landscape conditions on travel rates, we performed an experiment wherein study participants were timed while walking along a series of transects within a study area dominated by grasses, sagebrush and juniper. We compared resultant travel rates to LiDAR-derived estimates of slope, vegetation density and ground surface roughness using linear mixed effects modelling to quantify the relationships between these landscape conditions and travel rates. The best-fit model revealed significant negative relationships between travel rates and each of the three landscape conditions, suggesting that, in order of decreasing magnitude, as density, slope and roughness increase, travel rates decrease. Model coefficients were used to map travel impedance within the study area using LiDAR data, which enabled mapping the most efficient routes from fire crew locations to safety zones and provided an estimate of travel time.

Scale-Optimized Surface Roughness for Topographic Analysis

“…For example, while micro-topographic roughness was found to dominate much of the study area, if the larger-scale surface complexity associated with landform features were of specific interest, it would be possible to remove the impacts of smaller-scale roughness by selecting a larger r L value. If, instead, an application warrants focusing on surface roughness at shorter scales (e.g., Campbell et al's [36] recent examination of the impact of roughness on human travel through forested terrain), then it would be appropriate to select a relatively low r U value. It should be possible to similarly apply this technique to study regional-scale roughness patterns at the continental scale using available global DEM products.…”

A review of US wildland firefighter entrapments: trends, important environmental factors and research needs

“…slope steepness .248) are particularly dangerous to firefighters (Sharples et al 2010;Lahaye et al 2018c; owing to the rapid increase in spread rate caused by enhanced convective and radiant heating to unburned fuels (Rothermel 1985;Gallacher et al 2018). Additionally, if firefighters are surprised by specific fire runs on steep slopes, the potential for successful escape is further hampered by slower travel rates (Baxter et al 2004;Campbell et al 2017Campbell et al , 2019 and the requirement for larger safety zones (Butler 2014a). These topographic factors lead to an increase in both the likelihood of an entrapment and the probability of a fatality during an entrapment (Viegas and Simeoni 2011; Page and Butler 2017, 2018).…”

Wildfire Response Performance Measurement: Current and Future Directions

“…The fourth recommendation is to focus more directly on responder safety and exposure. Whereas we began from the notion of quantifying effectiveness in order to reduce instances of ineffective resource use (and thereby reduce unnecessary exposure), KPIs could be explicitly designed around factors such as safety zones and egress routes [51][52][53]. As an example, in-depth post-fire analysis could evaluate the frequency with which safety zones were pre-identified and determined suitable per new standards.…”