Event Scale Analysis of Streamflow Response to Wildfire in Oregon, 2020
Round 1
Reviewer 1 Report
• The aim of the paper is the analysis of the impact of large wildfires on the water basins present in the Pacific Northwest. The authors investigate the evolution of some fundamental characteristics of the flow of water of six watershed of the Oregon cascades before and after severe fires have occurred. The collected data show that the watershed runoff is modified in those with the largest fire impact. Further investigations are required to analyze the specific correlations between runoff variations and fire entity. While in urban areas the correlations between hydrological connectivity and spatial configuration have been thoroughly studied, less efforts have been dedicated to find similar outcome in landscape environments. The paper attempts to fill the gap from the perspective of wildfire influence, linking the spatial values of burned surface to hydraulic response of the soil. The expected results are not fully confirmed by the observations, as the median of the two flow parameters (peak runoff ratio and flow runoff ratio) does not change after the fire events. Larger variations of the point values are observed in those watersheds that have been more heavily impacted by wildfires. The work is methodologically sound and sufficiently detailed. A more thorough discussion of the uncertainties in the method would be beneficial, as some of the outcomes do not match the expected results. In Table 2 - please explain the meaning of high, medium, low. Please check spelling thoroughly.
Author Response
1. A more thorough discussion of the uncertainties in the method would be beneficial, as some of the outcomes do not match the expected results.
⇒ Author response: We greatly appreciate the reviewer comment. We elaborated the discussion section to address the uncertainties in our study design. See the added paragraph in section 4.4.
“While differences between watershed characteristics were observed (Table 1), such differences were not directly accounted for between watersheds. Specifically, the watersheds have wide-ranging permeability values (Table 1), dependent on unique combinations of geology and soils. Given that watersheds in the High Cascades (i.e., Clackamas and North Santiam) have buffering capacity due to groundwater input, post-fire stream response might have been delayed or have not been detected yet. Additionally, the size and location of burned areas, slope, and aspect are not consistent between watersheds, potentially challenging the comparability of post-fire runoff values.”
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In Table 2 - please explain the meaning of high, medium, low.
==> We explained the meaning of high, moderate, and low in Figure 1 and Table 2 captions.
“Low burn severity includes areas where surface organics have not been completely combusted, roots are intact, and some patches of grey ash are present. Moderate burn severity includes areas where some surface organics and roots have been consumed, some needles and leaves may remain, and patches of grey/black ash are present. High burn severity includes areas where almost all the organic groundcover has been destroyed, many surface roots are consumed, bare soil is exposed and soil structure has been disturbed, stumps and trees are completely burned out in places, and thick deposits of white and grey ash are present [52].”
“Characteristics of six burned watershed in Oregon with the total percentage burned and percentage of each burn severity class (low, moderate and high burned areas).”
- Please check spelling thoroughly. ==> We checked spelling thoroughly.
Reviewer 2 Report
Event Scale Analysis of Streamflow Response to Wildfire in Oregon, 2020
Will B. Long , Heejun Chang
This study attempt to detect changes in catchments runoff due to the effect of fires on the soil and changes in land vegetation cover. Although the role of climatic trends hides partially the post-fire effects on the hydrogeological cycle, sites having greater burned area and a greater area of high severity patches have a larger magnitude of change in “runoff ratio” values. Moreover, the largest changes in Event peak runoff ratio values occurred in the sites having the greatest percentage of burned area and the greatest percentage of high burn area. The paper represents in my opinion an important contribution to the study of the effects of fires on the hydrological cycle. The correlation between hydrological parameters and external events such as fires is a difficult task, due to high variability, the role of secondary forcing and the lack of continuous gauge data. However, it is appreciable to follow research about these topics, which can bring contribution to the scientific community. I have some suggestion that can maybe help the authors clarify the reading of the text and be more precise about how the data are presented. Here follows a list of suggestions; some of these are also reported in the attached pdf. Please check both revised files. Despite these requested suggestions, I think the paper can be accepted after minor revisions.
LINE 128, Section header 2.1: please remove the dot at the beginning of header. The same for headers 2.2, 2.5, 2.6, 2.9
LINE 150: A figure showing schematically the surface geology and a cross section would be useful. Given that you mention strong subsurface pathways, I would draw these pathways on the map or cross section. You may also choose to map geology for individual watershed; indeed, in section 2.3, you describe very accurately the geology of each watershed, but a map showing it would be really appreciated.
TABLE 1, About Permeable Geology %
I guess the permeable geology % is obtained from USGS web tool, so you get this information automatically. But which information were used to define permeability?is there a threshold of hydraulic conductivity which can tell you that a geological formation is permeable or not? What about geological formation alteration close to the surface? The permeability of a formation can vary between unaltered depth formation or a surface formation which can be subjected to pedogenesis, for example. Maybe your work does assume that these details can be neglected. However, I would declare these assumptions.
LINE 212 You wrote that the selected watersheds were those with unregulated streamflow to reduce anthropogenic impacts (LINE 181), and this is appreciable. But then, you mention that 8 dams are located into the watershed. So, I’m a little confused: what do you mean for unregulated streamflow? Even if the dam can have small storage capacity, they can have a not negligible influence on the streamflow, I think .
LINE 296: Sorry, I don't understand well: Qr is then the ratio between runoff (depth??) and precipitation amount?
LINES 640-644: I suggest to subdivide this sentence, which is very long and not easy to read.
Comments for author File: 
Comments.pdf
Author Response
1. LINE 128, Section header 2.1: please remove the dot at the beginning of header. The same for headers 2.2, 2.5, 2.6, 2.9 ⇒ Author response: Removed
2. LINE 150: A figure showing schematically the surface geology and a cross section would be useful. Given that you mention strong subsurface pathways, I would draw these pathways on the map or cross section. You may also choose to map geology for individual watershed; indeed, in section 2.3, you describe very accurately the geology of each watershed, but a map showing it would be really appreciated.
⇒ Author response: We created maps showing surface geology. Figure 1 (Surface geology of the study area displaying rocks of the Western Cascade Province and the High Cascade Province.) and Figure 2 (Generalized geological cross section of the study area where A) represents the High Cascade Province, which is more permeable, allowing for rapid groundwater exchange, while the Western Cascade Province, B), encourages surface runoff due to less permeable characteristics.) were inserted to aid the text and provide a visual representation of the surface and underlain geology.
3. TABLE 1, About Permeable Geology %
I guess the permeable geology % is obtained from USGS web tool, so you get this information automatically. But which information were used to define permeability?is there a threshold of hydraulic conductivity which can tell you that a geological formation is permeable or not? What about geological formation alteration close to the surface? The permeability of a formation can vary between unaltered depth formation or a surface formation which can be subjected to pedogenesis, for example. Maybe your work does assume that these details can be neglected. However, I would declare these assumptions.
⇒ Author response: Thank you for the comment. We added the following sentences.
Permeable geology obtained from USGS StreamStats was originally produced from a 1:2,500,000 map considering the percent basin surface area that contained high perme-ability geologic units, which were Pliocene volcanic rocks, Upper Tertiary andesite, and Quaternary volcanic rocks [49]. For soil permeability, we used watershed-wide average soil permeability (SOILPERM) in mm per hour, estimated with a data layer created from a 1:250,000 STATSGO map [50].
49. Schruben, P.G., Arndt, R.E., and Bawiec, W.J. (n.d.) Geology of the Conterminous United States at 1:2,500,000 Scale — A Digital Representation of the 1974 P.B. King and H.M. Beikman Map
50. Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at https://websoilsurvey.nrcs.usda.gov/. (accessed on 02 Febuary 2022
4. LINE 212 You wrote that the selected watersheds were those with unregulated streamflow to reduce anthropogenic impacts (LINE 181), and this is appreciable. But then, you mention that 8 dams are located into the watershed. So, I’m a little confused: what do you mean for unregulated streamflow? Even if the dam can have small storage capacity, they can have a not negligible influence on the streamflow, I think .
⇒ Author response: Thank you for the clarification. We modified the sentence in line 181 to the following.
These watersheds also have either unregulated streamflow or minimum impacts by upstream reservoirs to reduce the influence of anthropogenic alterations.
5. LINE 296: Sorry, I don't understand well: Qr is then the ratio between runoff (depth??) and precipitation amount?
⇒ Author response: Yes, it is the ratio between runoff depth and precipitation during a storm event
6. LINES 640-644: I suggest to subdivide this sentence, which is very long and not easy to read.
⇒ Author response: Thank you for the suggestion. We divided the sentence into two sentences.
“The role of drought on post-fire runoff dynamics was evident in the two control watersheds that both had declining Qp. This finding suggests that the magnitude of runoff responses could have been larger in these burned watersheds had the runoff enabling effect of reduced canopy interception on throughfall been dominated over evapotranspiration driven by high summer temperatures.”
** Other comments in the pdf document
- Line 48: How is fire intensity defined?
⇒ Author response: Thank you for the suggestion. The passage on burn severity and fire intensity has been elaborated to include the definition, “ Classes of burn severity are determined by assessment of remotely sensed imagery and/or field reconnaissance of watershed disturbances that are driven by fire intensity. The physical release of energy from combusting organic material over a period of time can cause a gradient of alterations to biomass and soil properties occurring during a wildfire event [7,8].”
2. Line 86: Not clear what landscape metrics means. Please explain better
⇒ Author response: Thank you, we have included more information to help the reader understand the concept of landscape metrics. The following sentence was added to clarify the use and purpose of landscape metrics:
“Additionally, landscape metrics can quantify subjective descriptions of landcover aggregation and density observed in spatial, categorical data to produce comparable indices.”
3. Line 154: A figure showing schematically the surface geology and a cross section would be useful. Given that you mention strong subsurface pathways, I would draw these pathways on the map or cross section.
⇒ Author response: Addressed this comment by adding the additional geological figures 1 and 2
4. Line 172: Sorry but I don't understand what salvage logging means. Could you explain or define it with other words?
⇒ Author response: Addressed this comment by including a more thorough definition of salvage logging:
“It is worth mentioning that extensive salvage logging, the commercial harvesting of burned trees, was undertaken shortly after fire, primarily concentrated on state managed lands, but specific information about the extent was not available at the time of study and not accounted for herein.”
5. Line 203: I guess the permeable geology % is obtained from USGS web tool, so you get this information automatically. But which information were used to define permeability?is there a threshold of hydraulic conductivity which can tell you that a geological formation is permeable or not? What about geological formation alteration close to the surface? The permeability of a formation can vary between unaltered depth formation or a surface formation which can be subjected to pedogenesis, for example. Maybe your work does assume that these details can be neglected. However, I would declare these assumptions.
⇒ Author response: see our responses above
6. Line 220: This reference should be numbered.
⇒ Author response: This has been remedied.
7. Table 2: the sum of low, moderate and high should be 11.3%
⇒ Author response: The total percentage of burned Clackamas watershed was corrected.
8. Line 296: Sorry, I don't understand well: Qr is then the ratio between runoff (depth??) and precipitation amount?
⇒ Author response: Please see our responses above.
