|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?”|
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.
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.