Atmospheric circulation changes and their impact on extreme sea levels around Australia

Colberg, Frank; McInnes, Kathleen L.; O'Grady, Julian; Hoeke, Ron

doi:https://doi.org/10.5194/nhess-19-1067-2019

Articles | Volume 19, issue 5

https://doi.org/10.5194/nhess-19-1067-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/nhess-19-1067-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 5

Research article

|

21 May 2019

Research article |

| 21 May 2019

Atmospheric circulation changes and their impact on extreme sea levels around Australia

Frank Colberg, Kathleen L. McInnes, Julian O'Grady, and Ron Hoeke

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Final revised paper (published on 21 May 2019)
Preprint (discussion started on 26 Mar 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'review of nhess-2018-64', Anonymous Referee #1, 05 Aug 2018
- AC1: 'response to referee one', Ron Hoeke, 16 Oct 2018
RC2: 'Review on Atmospheric Circulation Changes and their Impact on Extreme Sea Levels around Australia', Anonymous Referee #2, 04 Sep 2018
- AC2: 'repsonse to reviewer two', Ron Hoeke, 16 Oct 2018

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (23 Oct 2018) by Joaquim G. Pinto

AR by Lorena Grabowski on behalf of the Authors (07 Jan 2019) Author's response

ED: Referee Nomination & Report Request started (07 Jan 2019) by Joaquim G. Pinto

RR by Anonymous Referee #1 (19 Jan 2019)

Suggestions for revision or reasons for rejection

Dear Editor:
The paper has improved and in my opinion is publishable with minor revision (suggested, but not strictly needed).

It has the shortcoming that it remains largely inconclusive as future climate change is concerned. It is not clear whether future changes of storm surge maxima are not found in the simulations, because they are indeed small or because models are not reliable at reproducing them (note the substantial underestimation of extreme water levels in figure 4). I think that the reasons for lack of significant climate change signal could have been discussed more extensively, thought the authors identify regimes (the subtropical ridge and the northwest Monsoon) that are playing a role.

This work is anyway of some interest and it extends the results by Vousdoukas et al 2018.

Methodologically I see some minor points that could be more convincingly discussed and some minor change could easily improve the paper
- The motivation for the 20-year length of the analyzed period.
Page 5, line 9-14 Authors write “The twenty-year time slices were chosen to align the hydrodynamic model output to wave model simulations described in Hemer and Trenham [2016] with the aim to combine hydrodynamic extremes with wave-induced extremes (e.g. wave setup or runup) in future work.”
To me this looks a weak justification: having a longer period would not have prevented this planned future work

And further “The 20-year time slices are deemed adequate for assessing how large scale circulation changes will affect the drivers of ESLs around much of the Australian coast where seasonally varying weather systems are a major cause of extreme sea levels.” I think this is also weak as extreme weather frequency is affected by multidecadal variability. Could references be added to support that “20-year time slices are deemed adequate“?

- Neglecting of the tide-surge component, is acceptable because their computation would have been expensive, and benefits on climate change detection arguable, however:
Page 5 at line 20-21 authors write " [tide-surge interaction] may impact substantially on an individual surge event, [but] it does not change the surge statistics over a period of years to decades” . If it impacts significantly individual events, why it has no effect on the statistics? Even though it will not change the mean surge level, it would make the distribution broader or narrower, therefore eventually, increasing ordecreasing extreme values
Further, (figure 4) extreme surges are underestimated in the model simulation and this might explain why tide-surge interaction is weak.

Other points:
- at Line 1-2 at page 8 “some evidence points towards this peak being generated by a coastally trapped wave (CTW).” …It is not clear what is the evidence.

- At line 17 page 3
The conclusions Lionello et al are not reported fully (just read the last sentence in the abstract of that paper). The sentence “, but mass addition will likely determine an increase of the water level maxima” should be added

I see that the authors have considered only a selection of the referenced that I had previously suggested, but this is an acceptable choice of them

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RR by Anonymous Referee #2 (28 Jan 2019)

ED: Publish subject to minor revisions (review by editor) (31 Jan 2019) by Joaquim G. Pinto

AR by Anna Wenzel on behalf of the Authors (14 Feb 2019) Author's response Manuscript

ED: Publish subject to technical corrections (19 Feb 2019) by Joaquim G. Pinto

AR by Ron Hoeke on behalf of the Authors (27 Feb 2019) Author's response Manuscript

Post-review adjustments

AA: Author's adjustment | EA: Editor approval

AA by Ron Hoeke on behalf of the Authors (02 May 2019) Author's adjustment Manuscript

EA: Adjustments approved (06 May 2019) by Joaquim G. Pinto

Short summary

This study investigates coastal sea level variability and extremes around Australia, taking into account historical conditions and future atmospheric changes. Modelling suggests changes in future extreme sea levels may occur. A southward movement of the subtropical ridge leads to reduced sea level extremes in many areas, while changes over the Gulf of Carpentaria are largest and positive during austral summer in two of four simulations, likely associated with changes in the northwest monsoon.