Infrastructure Post-fire Debris Flow Vulnerability

Innovative methods to assess the vulnerability of transportation and other infrastructure to post-wildfire debris flows

Scope

The post-fire debris flow infrastructure vulnerability project is developed by ASU's Resilient Infrastructure Lab in partnership with UCLA's Institute of Transportation Studies. The project has focused on developing innovative methods for assessing the vulnerability of roadways and other infrastructure to wildfires and post-fire debris flows. Case studies have focused on California and Arizona. The research has produced a first-of-its-kind probabilistic assessment of roadway infrastructure post-fire debris flow risk, considering not only the likelihood of additional fires, but also precipitation and the characteristics of watersheds that ultimately lead to debris flows that impact stormwater management systems. Efforts are underway to expand the work to other infrastructure including railways and power transmission.

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 downscaled climate change hazards, precipitation patterns, transportation infrastructure, geography, and soil features of the watershed. These datasets are forced into an empirical post-fire debris hazard assessment model developed by geologists. The empirical model is used to estimate the basin level debris-flow probability and volume. Combined with the transportation infrastructure spatial distribution and betweenness centrality characteristics, the results from post-fire debris hazard assessment are used to identify the vulnerability of roadways.

Current and Future Fire Risk Assessments

Existing fire risk data and climate change forecasts.

Geologic and Vegetative Conditions

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

Watershed Hydrologic Assessment

Watershed hydrologic models are applied to estimate waterflow pathways and intensities.

Infrastructure Analysis

Infrastructure layers focus roadways (arterials and highways) and their intersections with streamflows.

Infrastructure Use

Measures of traffic flow can be applied to assess criticality of roadway links.

Transportation Vulnerability Assessment

The joining of geologic, vegetative, fire, infrastructure topology, and infrastructure conditions produce the vulnerability assessment.

Arizona Research

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.

The Arizona research is published in the journal Sustainable and Resilient Infrastructure. See the Selected Documentation section below for direct access to the article.

California Research

The California research is developing with final results expected in summer 2020. We are comparing post-fire debris flow risk across the state today against future scenarios.

Preliminary results indicated that:

Under current climate situation, when increasing precipitation intensity, the number of assets with post-fire debris risk increased.
Under the RCP 4.5 climate change scenario, for the HadGEM climate model, more infrastructures would be exposed to post-fire debris risk compared to today.

Image shows preliminary results for the current situation, under a 10-year intensity precipitation event (darker blue implies greater risk of post-fire debris flow).