Can riparian vegetation shade mitigate the expected rise in stream temperatures due to climate change during heat waves in a human-impacted pre-alpine river?

Trimmel, Heidelinde; Weihs, Philipp; Leidinger, David; Formayer, Herbert; Kalny, Gerda; Melcher, Andreas

doi:https://doi.org/10.5194/hess-22-437-2018

Articles | Volume 22, issue 1

https://doi.org/10.5194/hess-22-437-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-22-437-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 22, issue 1

Research article

| Highlight paper

|

18 Jan 2018

Research article | Highlight paper |

| 18 Jan 2018

Can riparian vegetation shade mitigate the expected rise in stream temperatures due to climate change during heat waves in a human-impacted pre-alpine river?

Heidelinde Trimmel, Philipp Weihs, David Leidinger, Herbert Formayer, Gerda Kalny, and Andreas Melcher

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Final revised paper (published on 18 Jan 2018)
Preprint (discussion started on 23 May 2016)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Can riparian vegetation shade mitigate the expected rise in stream temperatures during heat waves in a pre-alpine river? By Trimmel et al.', Anonymous Referee #1, 28 Jul 2016
- AC1: 'Response to RC1', Heidelinde Trimmel, 21 Aug 2016
SC1: 'energy flux direction', Heidelinde Trimmel, 30 Jul 2016
SC2: 'scientific novelty, aims and scope', Heidelinde Trimmel, 04 Aug 2016
RC2: 'Interactive comment on “Can riparian vegetation shade mitigate the expected rise in stream temperatures during heat waves in a pre-alpine river?” by H. Trimmel et al. Anonymous Referee #2', Anonymous Referee #2, 22 Aug 2016
- AC2: 'Response to RC2', Heidelinde Trimmel, 06 Oct 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (29 Aug 2016) by Anas Ghadouani

AR by Heidelinde Trimmel on behalf of the Authors (06 Oct 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Oct 2016) by Anas Ghadouani

RR by Anonymous Referee #3 (19 Dec 2016)

Suggestions for revision or reasons for rejection

General comments:
The authors appear to have responded to earlier reviewer suggestions. I find the paper fairly cohesive and understandable. The main message is that careful predictions made using the model Heat Source indicate that the river Pinka will likely warm as a consequence of global warming, and by the end of the century even full shading will be insufficient to prevent temperature increases during 20-year return events of even 2 °C.

The two aspects that I struggled with most in the paper were understanding individual sentences (suggested edits included) and coming to grips with results that suggested a 100% removal of vegetation would have less of an effect on stream temperatures than an increase in air temperature due to climate change. This point would be clarified if there were some other variable (e.g., vegetation density, percent shade, etc.) that readers could use to better understand the available shade for the STQ runs. Additionally, more information on the distribution of the bankfull width would be useful; if most of the river had 4m bankfull widths, I would expect that vegetation could feasibly grow to an extent that the entire stream could be shaded. If the majority of the stream had bankfull widths of 30 m, I would expect additions/removals of shade to have far less of an impact on stream temperatures.

Specific comments:
Page 1 Line 12: You use a passive voice in the first sentence. Start with “We simulated the influence…”
Page 1 Line 28: change to “the occurrence of many species”
Page 1 Line 30: provide a citation to support the “river continuum disruption” sentence
Page 1 Line 31: Zoonoses are diseases that can be transmitted from animals to people. Is the statement here indicating that major fish kills could result in disease transmission to people? Please clarify.
Page 1 Line 33-34: This sentence is unclear. I cannot tell what it means.
Page 2 Line 9: change “temperatures” to “temperature”
Page 3 Line 9: change “neither groundwater” to “neither change in groundwater”
Page 3 Line 10: deleted “change”
Page 4 Line 7: change “these” to “this”
Page 5 Line 2: It is not clear on what preliminary work has been done.
Page 5 first paragraph: This paragraph needs to be revised. Try changing the sentences to an active voice. “Holzapfel et al. (2015) continuously recorded vegetation cover…”
Page 5 Line 2: What is meant by “during a different article by Trimmell”?
Page 5 Line 5: change to “these data were”
Page 5 Line 7: change to “Heat Source was further used”
Page 5 Line 8: What is meant by “uniform reach”? What aspects of it were uniform? In other portions of the manuscript the substrate is described as not being uniform, and the vegetation cover varies as well. Also, identify in this sentence that the Pinka is the target river.
Page 5 Line 27: What is the HISTALP?
Page 6 Line 22: change “good” to “met” and after “fit” add “were appropriate” if that statement is still true.
Page 7 Line 3: This sentence is awkward. I suggest changing it to: “… conditions at the reference station data were extracted from the regional…”, add a comma after “Remo”, and delete text after the closing parenthesis. Provide a citation for ECHAM 5, as it is not introduced before this point.
Page 7 Line 5: change “, therefore” to “; therefore,”
Page 7 Line 8: rephrase the statement “area encompassing the area under investigation”.
Page 7 Line 29: change “situation was taken” to “data were obtained”.
Page 8 Line 9: change “which is corresponding” to “which corresponds”
Page 8 Line 16: change “were prevailing” to “prevailed”
Page 8 Line 19: What is meant by a “change” in discharge? Positive or negative change? The sentence indicates that any change of 0.1 m3/s will lead to an increase in stream temperature. Is this what is meant? Also, I am not convinced that the model is sensitive: a 0.1 m3/s change in discharge is a 55% increase or decrease for the upstream model boundary and still a sizable change for the downstream boundary (13%). Also, where did temperatures increase by 0.4 C? Was this at the upstream boundary, downstream boundary, or at the station in the middle?
Page 8 Line 22: Please clarify what is meant by MLF. The statement “average discharge of all discharges below the 5% discharge” is not helpful. What are the time periods in question that are being used to make these assessments? Is this annual or on a daily basis? The word “were” on line 29 suggests that there are multiple MLF values that are being used.
Page 9 Line 1: I am not clear on how the moving average was calculated. Over what timeframe?
Page 9 Line 5: Who measured the discharge and temperature during the 2013 episode? Was it the current set of authors?
Page 9 Line 6: Please clarify “boundary. adding" The sentence starting with “adding” is incomplete.
Page 9 Line 10: Change beginning of sentence to “As mentioned,”
Page 9 Line 13: “changes in water temperature”: where along the river were these changes found?
Page 9 Line 15: What is meant by “mere”? Does it mean that topographic shade contributes little to the temperature, or that it contributes more than might have been anticipated?
Page 10 Line 7: I believe this paragraph contains errors and can be cleaner. Should Fig. 2a actually be Fig 2b? Is “conduction” referring to 2f? On line 13 (should this be appended to the end of line 12?) should 2f be 2d? Finally, what is this paragraph referring to? STQ? Please clarify and check.
Page 11 Line 33: Change “supposed” to “supposing” Make the same change in the next paragraph as well.
Page 12 Line 5: add “for” between “fully the”
Page 12 Line 30: Why did the addition and removal of trees become roughly the same between distances 53 – 60? Why do we see the pattern mentioned? Is this due to a lack of trees along the Pinka between distances 25-53?
Page 13 Line 6: change “temperature difference” to “temperature the difference”
Page 13 Line 12: This sentence contains many qualifiers. It is difficult to understand. Can it be simplified?
Page 14 Line 11: This sentence relates to my general comments statement: why are these streams only warming by 1.8 C when all shade is removed? Yes, some studies (examining much shorter reaches) only see increases of this amount following complete canopy removal, but others see increases of even 10 C (Brown 1969 and Brown and Kryegier 1970). Again, this relates to understanding what the current shade levels are over the river.
Page 14 Line 34: Change “good” to “well”
Page 15 Line 20: change “showed to aggravate” to “aggravated” or “was shown to aggravate”

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RR by Anonymous Referee #4 (12 Feb 2017)

Suggestions for revision or reasons for rejection

Review of “Can riparian vegetation shade mitigate the expected rise in stream temperatures due to climate change during heat waves in a pre-alpine river?”

General Comments
This study evaluates the role of vegetation shading in mitigating the rise in stream temperature under climate change. The authors have evaluated 3 vegetation scenarios with varying degree of shading (zero, normal and maximum vegetation) using 1D energy balance and hydraulic model Heat Source (Boyd and Kasper 2003) for the river Pinka located in the eastern Austrian Alps. The Heat Source model was calibrated and validated by the lead author and results have already been published in the journal of Meteorologische Zeitschrift (Trimmel et al. 2016). Surprisingly, Trimmel et al. (2016) also evaluated the influence of shading using identical vegetation scenarios [no vegetation (V0), maximum vegetation (V100) and current condition (STQ)] along with few additional topographic shading scenarios [No topography (T0), no river bank (B0)]. The findings related to sensitivity of stream temperature to shading from the earlier paper have been summarized in section 2.4.
The authors argue and I quote “While in the previous study of Trimmel et al. (2016) only the propagation of uncertainties of input parameters on the mean stream temperature of a 22.5 km long reach during the heat episode of 2013 was analysed, here the longitudinal distribution of a more diverse section including the headwaters of the river Pinka was shown and discussed.” While this is true and this paper does bring additional analysis in terms of future climate change scenarios, one may have to wonder on the novelty and scientific contribution of this paper. Can’t we use the sensitivity results reported by Trimmel et al. (2016), also summarized in this paper on page 9 section 2.4, to infer the role of shading in mitigating future warming?
As for as mitigating the effects of future warming by shading is concern what is the mechanism of increased shading under warmer climate? How can we have maximum vegetation height and density, when air temperature increases under the climate change scenario used in this study and a constant value of discharge? What about the effects of increased riparian vegetation and air temperature on discharge? Even if you ignore the significant (10-15% as reported on page 5 section 2.1) changes in precipitation, vegetation and air temperature alone can modulate discharge and create a feedback with stream temperature. Even when considering the vegetation shading as end-member scenarios these feedback processes must be accounted and discussed.
Introduction is poorly re-written and can be condensed. Too much emphasis on discussing trends should be avoided. In the methodology section, the authors rely too much on readers’ knowledge and reference to the earlier work. This paper should stand on its own. The model used in this study should be clearly explained and well justified. Information related to model calibration and validation should be reported as well. It is unclear for readers that if the authors calibrated the model or they used the calibrated model. How were the vegetation height and density sampled?
The language of the manuscript is VERY poor and not suitable for a publication. The paragraphs lack gradual transition and often end with one sentence. Stating how this manuscript is different from another is not a great way to start “Results” section. Both results and discussion are very hard to follow, sorry.

Specific Comments
Pg1, line 27: This sentence needs a reference, “Stream temperature and assemblages of fish and benthic invertebrates …”.
Pg2, lines 25-27: this sentence is too long. Please break it into two sentences. “While net short wave radiation …”
Pg2, lines 26-27: Change “air humidity” and “wind” to vapor pressure and wind speed, respectively.
Pg2, lines 28-30: Please reword and revise.
Pg2, line 34: Move “Since 1980” to the end of the sentence.
Pg3, line 23: one sentence cannot be a paragraph.
Pg4, line 6: Revise and reword this sentence.
Pg4, line 6: Again, one sentence cannot be a paragraph.
Pg4, lines 18-20: adding discharge to a regression model may or may not increases the model performance.
Pg4, line 21-23: Again, this paragraph has only two sentences.
Pg5, line 27: “air temperature rose …” needs a reference.
Pg5, lines 31-33: This sentence is too long and vague.
Pg5, line 33: What do you mean by this sentence “Existing data sets and parameters obtained from Austrian authorities and the literature were completed with field surveys and measurements.”? Who are Austrian authorities? Are the data sets publicly available? If so you need to provide the link. How did you complete it?
Pg8, line 17: What does DFS stand for?
Pg8, line 19: “A change in discharge of …” increase or decrease?
Fig. 1: add geographic reference
Fig 2: very messy, legends on top of the lines
Fig. 3: Run statistical significance test and report results with the figure. Right now it is unclear whether STQ is significantly different from V0.

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ED: Reconsider after major revisions (further review by Editor and Referees) (03 Mar 2017) by Anas Ghadouani

AR by Heidelinde Trimmel on behalf of the Authors (13 Apr 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Apr 2017) by Anas Ghadouani

RR by Anonymous Referee #3 (17 Nov 2017)

Suggestions for revision or reasons for rejection

The authors of the paper “Can riparian vegetation shade mitigate the expected rise in stream temperatures due to climate change during heat waves in a pre-alpine river?” incorporated earlier suggested changes to their manuscript. I found this version easier to understand and appreciate the effort the authors have put forward.

I have only suggestions or concerns that I consider warrant minor revision. My two main suggestions are for the authors to 1) state that the results of this study are derived from a highly altered stream system, and 2) clarify how they constructed their vegetation scenarios and provide some means for readers to assess how realistically these scenarios could be realized. I expand upon these points below.

A central message for this paper, from the abstract, is that “[t]he result showed clearly that riparian vegetation was not able to fully mitigate the predicted temperature rise caused by climate change[.]” However, as I can discern from page 9 lines 15-16, the authors examined increased shade given no change in land use pressure. The river Pinka is highly altered, as the authors well document. Therefore, I believe that the authors need to highlight the caveat, possibly in the title and certainly in the abstract, that this stream is highly altered and therefore regardless of how vegetation develops or is enhanced where it currently exists, it cannot mitigate the effects of increased air temperature on stream temperature. I believe that highlighting this point will help readers understand the sort of riparian conditions under consideration here. The abstract does not indicate, except indirectly in the last sentence, the current state of the river or the limitations imposed on the V100 model. I suggest a rewording or re-examination of findings throughout the manuscript to ensure that readers understand that the results pertain to a highly altered system, unlikely to receive riparian restoration in developed areas.

On page 9, please clarify the vegetation scenarios. The sentence on lines 8-10 seems critical, yet I cannot understand what it is trying to convey. “Potential changes are most likely caused by different vegetation management strategies as intentional clearings, plantations or mowing.” Did the authors model a change in riparian characteristics by altering a mowing regime, the plantation characteristics or by allowing clearings to regrow? Or were these left unaltered, due to “no relief in land use pressure” (line 16)? In other words, what specifically was done to model V100? What areas were left unaltered, and in what stream areas was vegetation enhanced? Also, readers would benefit from some linkage between vegetation density values used in the different scenarios and observed vegetation density values. It would be useful to understand what the mean vegetation density value and range for STQ was, as well as the vegetation density value(s) at the upstream least-altered sites. Similarly, please provide more information on the plausibility of V100’s 90% vegetation density. What would be required to achieve this level of density? Is it a realistic restoration target?

Specific comments:
P.1 line 23: Not sure what is meant by “efficient.” Replace with “effective.”
P.3 line 28-29: citations needed.
p.8 line 25: delete “)”
p.11 line 24: Not sure what “Fig. f2h” refers to
p.13 line 31: space between “panel” and “the”
p. 14 line 18: change “where” to “were”
p. 14 line 16: please clarify “maximum temperatures could lead to increase at a higher rate”
p. 15 line 14: change “For the V0 scenario low” to “For the V0 scenario relatively low”
p. 15 line 21: I think a “)” is missing
p. 17 line 1: what is meant by “go line”?
p. 17 line 16: change “In cloud” to “Under cloudy”

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ED: Publish subject to minor revisions (review by editor) (18 Nov 2017) by Anas Ghadouani

AR by Heidelinde Trimmel on behalf of the Authors (22 Nov 2017) Author's response Manuscript

ED: Publish as is (26 Nov 2017) by Anas Ghadouani

AR by Heidelinde Trimmel on behalf of the Authors (27 Nov 2017)

Short summary

In eastern Austria, where air temperature rise is double that recorded globally, stream temperatures of a human-impacted river were simulated during heat waves, as calculated by regional climate models until 2100. An increase of up to 3 °C was predicted – thus exceeding thresholds of resident cold-adapted species. Vegetation management scenarios showed that adding vegetation can reduce both absolute temperatures and its rate of increase but is not able to fully mitigate the expected rise.