An official website of the United States government
This data release contains two debris-flow inventories summarizing observations from burned and unburned areas in the western Cascade Range of Oregon (OR). The burned inventory focuses on debris flows that occurred during the first two years after the 2020 Archie Creek, Holiday Farm, Beachie Creek/Lionshead, and Riverside fires (OR_field_observations.csv). The unburned inventory (1995-2022) focuses on debris flows in the same areas (excluding the Riverside Fire). The inventories are derived from field observations (OR_field_observations.csv) and aerial imagery (OR_imagery_observations.csv). They include mapped debris-flow initiation locations, descriptions of the inferred initiation process, other notable site characteristics, and rainfall data. Locations of debris flows observed after wildfires are also linked to USGS postfire debris-flow hazard assessments (USGS, 2022; Staley and others, 2017; Thomas and others 2023). Rainfall characteristics for each debris flow in the inventory are derived from the closest rainfall gage to an observed debris flow (gage_locations.csv). Peak rainfall rates during the known time window of debris-flow initiation are reported for durations of 15 minutes, 30 minutes, 60 minutes, 12 hours, 24 hours, 36 hours, and 48 hours. More detailed explanations of the headers for each of these csv files can be found within the README_csvname.txt file. References: Landslide Hazards Program. (n.d.). Emergency assessment of post-fire debris-flow hazards. U.S. Geological Survey. https://landslides.usgs.gov/hazards/postfire_debrisflow Staley, D. M., Negri, J. A., Kean, J. W., Laber, J. L., Tillery, A. C., and Youberg, A. M., 2017, Prediction of spatially explicit rainfall intensity–duration thresholds for post-fire debris-flow generation in the western United States. Geomorphology, 278, 149–162. https://doi.org/10.1016/j.geomorph.2016.10.019 Thomas, M. A., Kean, J. W., McCoy, S. W., Lindsay, D. N., Kostelnik, J., Cavagnaro, D. B., Rengers, F. K., East, A. E., Schwartz, J. Y., Smith, D. P., and Collins, B. D., 2023, Postfire hydrologic response along the Central California (USA) coast: insights for the emergency assessment of postfire debris-flow hazards. Landslides, 20, 2421-2436. https://doi.org/10.1007/s10346-023-02106-7
more »
« less
This content will become publicly available on June 1, 2026
Rainfall Thresholds for Postfire Debris‐Flow Initiation Vary With Short‐Duration Rainfall Climatology
The size, frequency, and geographic scope of severe wildfires are expanding across the globe, including in the Western United States. Recently burned steeplands have an increased likelihood of debris flows, which pose hazards to downstream communities. The conditions for postfire debris‐flow initiation are commonly expressed as rainfall intensity‐duration thresholds, which can be estimated given sufficient observational history. However, the spread of wildfire across diverse climates poses a challenge for accurate threshold prediction in areas with limited observations. Studies of mass‐movement processes in unburned areas indicate that thresholds vary with local climate, such that higher rainfall rates are required for initiation in climates characterized by frequent intense rainfall. Here, we use three independent methods to test whether initiation of postfire runoff‐generated debris flows across the Western United States varies similarly with climate. Through the compilation of observed thresholds at various fires, analysis of the spatial density of observed debris flows, and quantification of feature importance at different spatial scales, we show that postfire debris‐flow initiation thresholds vary systematically with short‐duration rainfall‐intensity climatology. The predictive power of climatological data sets that are readily available before a fire occurs offers a much‐needed tool for hazard management in regions that are facing increased wildfire activity, have sparse observational history, and/or have limited resources for field‐based hazard assessment. Furthermore, if the observed variation in thresholds reflects long‐term adjustment of the landscape to local climate, rapid shifts in rainfall intensity related to climate change will likely induce spatially variable shifts in postfire debris‐flow likelihood.
more »
« less
- PAR ID:
- 10631947
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 130
- Issue:
- 6
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Predicting where runoff‐generated debris flows might occur during rainfall on steep, recently burned terrain is challenging. Studies of mass‐movement processes in unburned areas indicate that event locations are well‐predicted by rainfall anomaly,R*, in which peak observed rainfall is normalized by local rainfall climatology. Here, we use remote and field methods to map debris flows triggered within the 2020 Dolan Fire burn area in coastal California, demonstrate that a short‐durationR*metric predicts debris‐flow occurrence more effectively than absolute peak intensity or longer‐duration rainfall metrics, and show that incorporating anR*criterion into an existing debris‐flow likelihood model can reduce false positive predictions and improve accuracy. We testR* at three other climatically distinct fires in California, demonstrating its utility for mapping likely debris‐flow locations in different climates. We also consider howR*can benefit postfire debris‐flow prediction given recent increases in climatological variability within individual burn perimeters.more » « less
-
Pirulli, M; Leonardi, A; Vagnon, F (Ed.)Wildfire makes landscapes more vulnerable to debris flows by reducing soil infiltration capacity and decreasing vegetation cover. The extent to which fire affects debris-flow processes depends on the severity of the fire, the climatology of intense rainfall, the pre-fire plant community, and sediment supply, among other factors. As fire expands into new plant communities and geographic regions, there is a corresponding need to expand efforts to document fire-induced changes and their impacts on debris-flow processes. In recent years, several large wildfires have impacted portions of the Sonoran Desertscrub plant community in Arizona, USA, a plant community where fire has been historically infrequent. Following two of these fires, we monitored debris-flow activity at the watershed scale and quantified wildfire-driven changes in soil hydraulic properties using in-situ measurements with mini disk tension infiltrometers. Results indicate that rainfall intensity-duration thresholds for the initiation of post-fire debris flows in recently burned watersheds within the Sonoran Desertscrub plant community are substantially greater than those in nearby areas dominated by other plant communities, such as chaparral. Results provide insight into the impact of fire on debris-flow processes in a plant community where it is likely to be more impactful in the future and help expand existing post-fire debris flow databases into a plant community where there is a paucity of observations.more » « less
-
Pirulli, M.; Leonardi, A.; Vagnon, F. (Ed.)Debris flows pose a serious threat to human life and infrastructure in downstream areas following wildfire. This underscores the necessity for having a hazard assessment framework in place that can be used to estimate the impacts of post-wildfire debris flows. Current hazard assessments in the western United States (USA) use empirical models to assess the volume of potential post-wildfire debris flows. Volume models provide information regarding the magnitude and potential downstream impacts of debris flows. In this study, we gathered post-wildfire debris-flow volume data from 54 watersheds across the states of Arizona (AZ) and New Mexico (NM), USA, and compared these data to the output of a widely used empirical post-wildfire debris-flow volume model. Results show that the volume model, which was developed using data from the Transverse Ranges of southern California (CA), tends to overestimate observed volumes from AZ and NM, sometimes by several orders of magnitude. This disparity may be explained by regional differences between southern CA and AZ and NM, including differences in sediment supply. However, we found a power- law relationship between debris-flow volume and watershed area that can be used to put first-order constraints on debris-flow volume in AZ and NM.more » « less
-
Abstract. In steep wildfire-burned terrains, intense rainfall can produce large runoff that can trigger highly destructive debris flows. However, the abilityto accurately characterize and forecast debris flow susceptibility in burned terrains using physics-based tools remains limited. Here, we augmentthe Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to simulate both overland and channelized flows and assess postfiredebris flow susceptibility over a regional domain. We perform hindcast simulations using high-resolution weather-radar-derived precipitation andreanalysis data to drive non-burned baseline and burn scar sensitivity experiments. Our simulations focus on January 2021 when an atmospheric rivertriggered numerous debris flows within a wildfire burn scar in Big Sur – one of which destroyed California's famous Highway 1. Compared to thebaseline, our burn scar simulation yields dramatic increases in total and peak discharge and shorter lags between rainfall onset and peakdischarge, consistent with streamflow observations at nearby US Geological Survey (USGS) streamflow gage sites. For the 404 catchments located inthe simulated burn scar area, median catchment-area-normalized peak discharge increases by ∼ 450 % compared to the baseline. Catchmentswith anomalously high catchment-area-normalized peak discharge correspond well with post-event field-based and remotely sensed debris flowobservations. We suggest that our regional postfire debris flow susceptibility analysis demonstrates WRF-Hydro as a compelling new physics-basedtool whose utility could be further extended via coupling to sediment erosion and transport models and/or ensemble-based operational weatherforecasts. Given the high-fidelity performance of our augmented version of WRF-Hydro, as well as its potential usage in probabilistic hazardforecasts, we argue for its continued development and application in postfire hydrologic and natural hazard assessments.more » « less
