the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Augmentation and Use of WRF-Hydro to Simulate Overland Flow- and Streamflow-Generated Debris Flow Hazards in Burn Scars
- 1Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, 60208, USA
- 2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, 90095, USA
- 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
- 4Environmental Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
- 5Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, CO, 80309, USA
- 6NOAA/Global Systems Laboratory, 325 Broadway Boulder, Denver, CO, 80305-3328, USA
- 7Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL, 60208, USA
- 8University of California Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, CA, 95064, USA
- 9Program in Environmental Sciences, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA
- 10Department of Biological Sciences, Purdue University, 915 W State St, West Lafayette, IN 47907, USA
- 1Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, 60208, USA
- 2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, 90095, USA
- 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
- 4Environmental Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
- 5Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, CO, 80309, USA
- 6NOAA/Global Systems Laboratory, 325 Broadway Boulder, Denver, CO, 80305-3328, USA
- 7Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL, 60208, USA
- 8University of California Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, CA, 95064, USA
- 9Program in Environmental Sciences, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA
- 10Department of Biological Sciences, Purdue University, 915 W State St, West Lafayette, IN 47907, USA
Abstract. In steep wildfire-burned terrains, intense rainfall can produce large volumes of runoff that can trigger highly destructive debris flows. The ability to accurately characterize and forecast debris-flow hazards in burned terrains, however, remains limited. Here, we augment the Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to simulate both overland and channelized flows and assess postfire debris-flow hazards over a regional domain. We perform hindcast simulations using high-resolution weather radar-derived precipitation and reanalysis data to drive non-burned baseline and burn scar sensitivity experiments. Our simulations focus on January 2021 when an atmospheric river triggered numerous debris flows within a wildfire burn scar in Big Sur – one of which destroyed California’s famous Highway 1. Compared to the baseline, our burn scar simulation yields dramatic increases in total and peak discharge, and shorter lags between rainfall onset and peak discharge. At Rat Creek, where Highway 1 was destroyed, discharge volume increases eight-fold and peak discharge triples relative to the baseline. For all catchments within the burn scar, we find that the median catchment-area normalized discharge volume increases nine-fold after incorporating burn scar characteristics, while the 95th percentile volume increases 13-fold. Catchments with anomalously high hazard levels correspond well with post-event debris flow observations. Our results demonstrate that WRF-Hydro provides a compelling new physics-based tool to investigate and potentially forecast postfire hydrologic hazards at regional scales.
Chuxuan Li et al.
Status: final response (author comments only)
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RC1: 'Comment on nhess-2021-345', Paul Santi, 05 Jan 2022
General Comments
The paper is very well written and easy to follow, and it is a nice integration of modern modeling techniques and data for use in debris flow analysis.
I think a slight change in the declared focus of the paper will better highlight its value. Allow me to explain. At many points in the paper, the authors have gone to a lot of trouble to set up, run, and calibrate models that basically demonstrate the same things that have been said (and quantified) in other papers using much simpler analyses: debris flow volume and discharge increase multifold in burned areas, the hazard is concentrated in stream channels, and there is a lag between rainfall peaks and flow events, for example. However, the authors’ analyses provide some information that has not been clearly shown before. Importantly, they are able to create calibrated time graphs of streamflow and discharge. Also, they are able to compare their models with the USGS post-wildfire assessments to show differences (they refer to this in lines 652-656, but don’t give details of the analysis).
I think the paper would be stronger if they acknowledge early on that other research has demonstrated (and quantified) changes in volume, discharge, and lag. Then they could focus on the advantages offered by a more sophisticated, calibrated model. I think the discussion should also include a section on applying the model elsewhere. Is it realistic to do this for other sites, or is it too dependent on specific calibration parameters? How could a practitioner do this type of analysis? What does it offer a scientist that they do not already know? The discussion could also compare there model to the USGS model, using a modification to Figure 9, for example, to demonstrate and explain the important differences.
Specific Comments
Section 5.4 - I don’t feel that this is a strong section. It concludes that the hazards are greater in the burned area, and mostly in the channels, and that streamflow is elevated downstream in burned areas, which are not unique findings. Likewise, Figure 11 doesn’t come across as strongly as previous figures. I suggest dropping this section,.
line 489 ff - an interesting note, your modeled discharge increases by 3 or 4 fold matches field measured changes published in Brunkal and Santi for large drainage basins (I could not find the area for your drainage basins, since you include normalized values, but I assume they are more than 5 km^2) (Brunkal, H. and Santi, P., 2017, “Consideration of the Validity of Debris-Flow Bulking Factors,” Environmental and Engineering Geoscience, DOI: 10.2113/EEG-1774). See Figure 3 of this paper.
Technical Corrections
Figures 1, 7. and 9 could benefit from a bar scale.
Figure 9 - the legend is hard to understand. I assume the first bar is volume and the second is normalized volume?
- AC1: 'Reply on RC1', Chuxuan Li, 01 Feb 2022
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AC2: 'Reply on RC1', Chuxuan Li, 01 Feb 2022
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-345/nhess-2021-345-AC2-supplement.pdf
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RC2: 'Comment on nhess-2021-345', Anonymous Referee #2, 25 Jan 2022
The manuscript deals with assessment of the debris flow hazard in burned areas through simulations that used high-resolution weather radar-derived precipitation. The manuscript has sveral interesting points, and overall is well written. It is certainly worth to be considered for publication, but I have a couple of points which need to be clarified.
The first (and main) one regards the terminology used. I am afraid that, throughout the article, the term hazard is not used correctly. In my opinion, Authors are rather talking about susceptibility, and not hazard, the difference being that hazard should depict the probability of occurrence of a certain phenomenon not only spatially but also temporally. This latter issue (time) is not considered in the study. I suggest go back to the original definition by Varnes (1984) and UNESCO, and in later works as well, to clarify the meaning of susceptibility and hazard, and to change accordingly the terms in the manuscript.
Another point which needs more details is the description of the debris flows. Authors talk about several debris flows that occurred, and start to cite them in section 2.1. However, a clear description of the events, in terms of geology, morphology, morphometry, volumes is never properly given. This should be done the first time debris flows are mentioned (possibly in section 2.1) to let the reader understand the main characters of the events. For instance, were these debris fows individul phenomena, or did they start from multiple source areas? Further, were they channalized or openslope? More geomorphological info would be useful to understand the conditions under which the debris flows initiated and developed. Only at page 18 some info are provided, but these should appear much before than that, and be well organized, rather than distributed in different parts of the manuscript.
Other issues:
Figure 1 definitely needs a location map, showing where we are in California, and in USA. Authors give for granted that anaybody knows the site, but for an international journal a location map is always necessary.
Throughout the manuscript, references should be listed in chronological order when more than two references are cited.
Some incomplete or wrong references are present in the list. Please check at this regard the attached file.
Eventually, some minor issues are indicated in the accompanying file.
Overall, I evaluate positively the manuscript, which howevere needs to clarify the points outlined above, and recommend minor revisions.
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AC3: 'Reply on RC2', Chuxuan Li, 01 Feb 2022
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-345/nhess-2021-345-AC3-supplement.pdf
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AC3: 'Reply on RC2', Chuxuan Li, 01 Feb 2022
Chuxuan Li et al.
Chuxuan Li et al.
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