Hydrodynamic Model Ensembles for Climate Change Projections in Estuarine Regions

Round 1

Reviewer 1 Report

The work reported here seems to have been well thought-through and executed. However, much of the content is a repeat of work presented in a paper by the same authors in Frontiers in Marine Science and I am not convinced that this adds a great deal to that previous paper, other than some specific results for the 2 estuaries not included there. Thus,  while the paper is reasonably well- written (excepting some odd English in places) it does not seem significant and will be of interest to few readers. My suggestion is that you draw out some points of more general interest about the methods used etc. perhaps including some critical evaluation of the hydrodynamic and climate models used.

Author Response

Dear Reviewer, thank you for your comments and suggestions that helped us to improve the manuscript.

Regarding the English language, and next to correcting the typos detected by Reviewer 2, a thorough review was performed to detect and correct any other errors.

Regarding the novelty of the paper, we included an explanation in the Introduction section that clarified that, to the best of our knowledge, the superensemble technique proposed in this work has not been applied to improve the numerical modelling forecasts of future hydrodynamic patterns in estuarine regions taking into account extreme water levels associated with RCPs defined by the IPCC. This manuscript intends to cover this lack of knowledge, distinguish this new approach when compared with our previous work in Frontiers in Marine Sciences. At the same time, the Discussion and Conclusions section was improved, including the limitations of the study regarding the selected climatic forcing and future works to be considered. In addition, an in depth explanation about the effects on the local conditions due to changes in the estuarine hydrodynamic patterns was included in the Discussion and Conclusions section. We expect that these changes will provide the submitted manuscript with interest not only for a local, but also for a wider audience.

Reviewer 2 Report

This work focuses on the hydrodynamics of two estuaries in Portugal (Douro and Minho), where they use numerical models for different scenarios to obtain ensemble forecasts for 2050 and 2100. There results provide insight on the different impacts of future sea level rise and extreme river flow discharge on these estuarine regions, with each of these effects playing different roles in the two regions. This is a very interesting and well presented work, which I believe is technically sound and ready for publication as is. Below I list some minor typos that I have found that the authors should correct before resubmitting.

page 2
line 52: change "resulting on" to "resulting in"

line 64: change "Being the estuarine biota highly" to "Given that the estuarine biota is highly"
line 81: change "over" to "on"
line 83: change "force" to "forcing"

page 3
line 129: change "separated" to "separate"

page 6
line 208: change "should to be" to "should be"

page 8
line 300: change "practical" to "practically"
line 301: change "upstream the mouth" to "upstream from the mouth"

Author Response

Thank you for your comments. All the typos detected by the Reviewer were corrected. Additionally, a thorough review of the English language was performed to detect any other typos/errors.

Reviewer 3 Report

The results presented by the Authors are based on the results of numerical modeling. The authors do not describe numerical models, but give clear references at paper. Many factors must be considered for numerical modeling of the flood zone. As I understood from the work, the Authors responded by doing it. The work gives that the model is adapted for the regions. However, I have a few questions.

1. I understand that bottom friction was taken into account for numerical modeling. However, this parameter depends on the material that is located on the bottom or shoreline. How this parameter was set. How the vegetation on the shore was taken into account.

2. Whether bottom changes were taken into account in the model. I.e. movement of bottom sediments processes.

   Thank you 

Author Response

Dear Reviewer, thank you for your comments.

Answering your questions, and regarding the bottom friction coefficient, it was calibrated by comparing the numerical models’ historical simulations with current velocity and water elevation in situ measurements for each estuary, scenario and numerical model considered. This calibration was performed not only for normal conditions but also for extreme events (floods). Several numerical simulations were performed with different bottom friction coefficients until achieving the most accurate results. These procedures, and the final coefficients selected, are described in more detail in publications 5,11,16 and 21. As can be seen in those publications, and considering the accuracy of the obtained results, there was no need to implement different bottom friction coefficient values depending on the sediment typology of the different estuarine regions. But, of course, we are aware that, if more measurement points were available and the sediment distribution along the estuaries was known, the performance of the models could be improved by distinguishing the friction coefficient between different sediments at bottom areas.

Regarding the estuarine margins, no different bottom friction was considered. This means that different margin configurations (vegetation, urban environments) was not taken into account, but estuarine banks effects on the bottom friction are included in the adopted bulk coefficient for all the estuary. For normal conditions (low river discharges), and due to the specificities of the selected estuaries, there is no significant difference in the modelling results when different friction coefficients are considered for the margins, but some differences could arise when considering extreme floods. Since the vegetation rises the bottom friction, if is not considered, worse flood effects could be expected. However, the numerical models’ calibration procedures revealed that the obtained results are quite accurate without considering different friction coefficients, and, therefore, the vegetation on the margins (see publications 5,11,16 and 21).

This manuscript presents the superensemble forecasting for future hydrodynamic scenarios. The superensemble was constructed with hydrodynamic numerical models, so the morphodynamics was not considered. The authors are of course aware about the bottom morphology changes that could be produced for the extreme river flow and sea level rise scenarios proposed; not including this dynamic is thus a limitation of this study. This is why a paragraph was added in the manuscript section 4 (Discussion and Conclusions) to notice that the fact that sediment transport was not considered could have a significant effect in the resulting water levels. Lower water levels than the ones predicted could be expected if a scouring of the estuarine sand spits are produced during an extreme event.

References:

5 - Iglesias I, Avilez-Valente P, Bio A, Bastos L. Modelling the Main Hydrodynamic Patterns in Shallow Water Estuaries: The Minho Case Study. Water 2019;11:1040. https://doi.org/10.3390/w11051040.

11 - Weber de Melo W, Pinho J, Iglesias I, Bio A, Avilez-Valente P, Vieira J, et al. Flood Risk Assessment at the Douro River Estu-ary. In: Kolathayar S, Mondal A, Chian SC, editors. Lect. Notes Civ. Eng. Climate Ch, Springer; 2022, p. 37–49. https://doi.org/10.1007/978-981-16-5501-2_4.

16 - Iglesias I, Venâncio S, Pinho JL, Avilez-Valente P, Vieira J. Two Models Solutions for the Douro Estuary: Flood Risk Assess-ment and Breakwater Effects. Estuaries and Coasts 2019;42:348–64. https://doi.org/10.1007/s12237-018-0477-5.

21 - Melo W, Pinho J, Iglesias I, Bio A, Avilez-Valente P, Vieira J, et al. Hydro- and Morphodynamic Impacts of Sea Level Rise: The Minho Estuary Case Study. J Mar Sci Eng 2020;8:441. https://doi.org/10.3390/jmse8060441.