Infrastructure Post-fire Debris Flow Vulnerability

Innovative methods to assess the vulnerability of transportation and power infrastructure to wildfires and post-fire debris flows

Scope

The fire and post-fire debris flow infrastructure vulnerability project is developed by ASU's Resilient Infrastructure Lab. The project is focused on developing innovative methods for assessing the vulnerability of roadways and power infrastructure to wildfires and post-fire debris flows. Case studies have focused on California and Arizona. The research has produced first-of-its-kind probabilistic assessments of roadway and power infrastructure fire and post-fire debris flow risk, considering the likelihood of fires and precipitation today and under climate change futures, and the characteristics of watersheds.

Camp Fire, 2018. Butte County, CA (Source: LANDSAT).

Model Inputs:

The 30-meter digital elevation model (DEM) provides the slope, ruggedness, and elevation range of topographical features. The DEM is also used to derive the stream networks and the watershed boundaries.
2 to 100 year Design storms.
Data on wildfire potential.
Soil data of clay content and liquid content to characterize ground properties.
Extreme precipitation and wildfire forecasts based on ensembles of Global Climate Models under climate change scenarios.
Subbasin watersheds .
Roadway networks and their betweenness centerality.

Characterizing the Vulnerability of Infrastructure

The vulnerability assessment uses datasets for current fire risk, downscaled climate change future risk, current and future precipitation patterns, infrastructure (roadways, transmission lines, and substations), geography, vegetation, and soil features. Analysis is performed on fine-scale watersheds. Current and future fire and precipitation risk are first compared. Next, the datasets are forced into an empirical post-fire debris hazard assessment model developed by USGS. The empirical model is used to estimate the debris-flow probability and volume for each watershed, including future climate uncertainty. Infrastructure asset importance (criticality) is characterized using network analysis betweenness-centrality measures. Vulnerability to fires and post-fire debris flows is then estimated as hazard risk and criticality. Results are validated against historical fire and post-fire debris events.

Current and Future Fire Risk Assessments

Existing fire risk data and climate change forecasts.

Geologic and Vegetative Conditions

Watershed geologic conditions include ruggedness, soil properties, slope, and vegetation.

Watershed Hydrologic Assessment

Hydrologic models are applied to estimate waterflow pathways and intensities.

Infrastructure Systems

Infrastructure layers focus on roadways, transmission lines, and substations.

Infrastructure Criticality

Measures of infrastructure asset importance are developed.

Infrastructure Vulnerability Assessment

Fire, precipitation, geologic, and vegetative conditions are used to produce hazard risk assessments and are joined with infrastructure layers including criticality measures.

Arizona Roadway Vulnerability

Probability of post-fire debris flows and flooding following a wildfire and 10 year - 10 minute percipitation event, in Arizona's 4FRI region.

Wildfires have grown in number, size and intensity in the American West and forecasts predict worsening trends. Evidence mounts that post-fire debris flows pose a major hazard to infrastructure, particularly roadways. Vulnerabilities of assets to post-fire flows requires consideration of geologic, vegetative, and hydrologic conditions. A model that considers environmental conditions, post-fire effects, and transportation asset use is developed, and applied to a fire prone region in Arizona. 17% of watersheds have a greater than 20% chance of post-fire debris movements and flooding under a minor precipitation event. Additionally, there is a greater than 50% probability of post-fire debris flows where recent fires have occurred, validating the underlying model. The model shows the vulnerability of infrastructure to environmental and technological variables, drawing attention to the need to manage the risk as a broader system.

Publication documenting our methods and results:
A Fraser, M Chester, and BS Underwood, Wildfire risk, post-fire debris flows, and transportation infrastructure vulnerability, 2022, Journal of Sustainable and Resilient Infrastructure, 7(3), pp. 188-200, doi: 10.1080/23789689.2020.1737785.

California Roadway Vulnerability

Post-wildfire debris flows represent a significant hazard for transportation infrastructure. The location and intensity of post-fire debris movements are difficult to predict, and threats can persist for several years until the watershed is restored to pre-fire conditions. This situation might worsen as climate change forecasts predict increasing numbers of wildfire burned areas and extreme precipitation intensity. New insights are needed to improve understanding of how roadways are vulnerable to post-fire flows and how to prioritize protective efforts. Using California as a case study, the vulnerability of transportation infrastructure to post-fire debris flow was assessed considering geologic conditions, vegetation conditions, precipitation, fire risk, and roadway importance under current and future climate scenarios. The results showed significant but uneven statewide increases in the number of vulnerable roadways from the present to future emission scenarios. Under current climate conditions, 0.97% of roadways are highly vulnerable. In the future, the ratio of vulnerable roadways is expected to increase 1.9-2.3 times in the Representative Concentration Pathways (RCP) 4.5 emission scenarios and 3.5-4.2 times in the RCP 8.5 emission scenarios. The threat of post-fire debris flow varies across the state, as precipitation changes are uneven. The vulnerability assessment is positioned to 1) identify, reinforce, and fortify highly vulnerable roadways, 2) prioritize watershed fire mitigation, and 3) guide future infrastructure site selection.

Publication documenting our methods and results:
R Li and M Chester, 2023, Vulnerability of California Roadways to Post-wildfire Debris-flows, Environmental Research Infrastructure and Sustainability, doi: 10.1088/2634-4505/acb3f5.

The results were initially developed in partnership and with support from the the UCLA Institute of Transportation Studies: Chester M and Li R, 2020, Vulnerability of California Roadways to Post-Wildfire Debris Flow, UCLA Institute of Transportation Studies, Report No. UC-ITS-2020-38, doi: 10.17610/T60W35.

California Power Vulnerability

Preliminary results (Feb. 2023): Vulnerability of power transmission and substation assets to fires and post-fire debris flows.

The State of California is experiencing serious challenges as fires cause catastrophic damage to infrastructures and communities. As the state invests in resilience efforts to protext power systems from fires and subsequent post-fire debris flows, it becomes critical to focus limited resources on the most vulnerable assets. In this project we assess the vulnerabity of power transmission lines and substations to wildfires and post-fire debris flows. We compare current fire and post-fire debris flow risk to several climate-impacted futures. In doing so we are able to see how vulnerability profiles of assets shift and where the state should prioritize resources for a changing future.