the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Aug 2026
Forecasting the 12 November 2019 Venice Acqua Alta event: the role of baroclinic compounding effects
Abstract. The northern Adriatic Sea is known to be threatened by extreme sea level events. Venice is exposed to these events, locally known as Acqua Alta, which cause the flooding of the historical city centre. Despite its relevance, a comprehensive analysis of extreme Acqua Alta events that considers all possible compounding drivers, including baroclinic contributions, is, to our knowledge, still missing. In this work, numerical results based on the Copernicus Marine Mediterranean Analysis and Forecasting System are analyzed to better understand the physical mechanisms underlying the 12 November 2019 Acqua Alta event and to assess individual processes playing a role in the event dynamics.
The novel finding of this study is the identification of the contribution of baroclinic dynamics. We estimate a net baroclinic contribution of 7 cm (4 %) to the 175 cm sea level peak. We show for the first time that internal seiches along the northern Adriatic slope contribute to the dynamics of the Acqua Alta event. Moreover, we identify a northern Adriatic density front and quantify its contribution to the time-mean positive northward sea level slope.
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Status: open (until 16 Oct 2026)
- RC1: 'Comment on egusphere-2026-4734', Anonymous Referee #1, 09 Sep 2026 reply
Data sets
Observed sea level data at the ISMAR tide-gauge ISMAR-CNR, Institute of Marine Sciences, Venice, Italy https://www.comune.venezia.it/it/content/3-piattaforma-ismar-cnr
Copernicus Marine Analysis and Forecasting System product Copernicus Marine Service https://doi.org/10.48670/mds-00359
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- 1
The paper addresses an important event and is generally well written. The modelling setup is interesting, and I appreciate the effort to separate the sea-level response into different components and to discuss the underlying dynamics. That said, I have several major concerns about the strength of the attribution and the consistency of some of the quantitative arguments. In its current form, I do not think the manuscript fully supports its main conclusions.
Main comments:
1. Attribution of the 7 cm difference
The manuscript appears to interpret the roughly 7 cm difference between MedFS and MedFS-BT at the event peak as the baroclinic contribution. I do not think this is sufficiently justified.
The two configurations differ in more than baroclinicity alone; they also involve changes in wave coupling, wind stress, bottom friction, and initialisation strategy. These differences are all potentially relevant at the centimetre level. As a result, the 7 cm signal cannot be attributed uniquely to baroclinic processes based on the present design.
At minimum, this needs to be stated much more cautiously, and the discussion should acknowledge the confounding model differences explicitly.
2. Relationship between the 7 cm and 3 cm estimates
The paper reports a 7 cm peak difference, while the front analysis gives a mean contribution of about 2.9 cm. The connection between these two numbers is not clear.
It is not obvious whether the offset applied in Sect. 2 removes the mean baroclinic setup or only part of it, and the reader is left unsure how the 3 cm front contribution should be related to the 7 cm peak difference. This point needs to be explained much more clearly.
3. Evidence for the internal seiche interpretation
The internal seiche interpretation is plausible, but the evidence is not yet convincing enough. The period appears to be inferred mainly from the model fields, and a 12-hour signal is close to the main tidal constituents. A spectral analysis, or at least a more direct diagnostic, would help considerably.
The relation between the identified oscillation, the filter bands used in the decomposition, and the “tides–seiches” component should also be clarified.
4. Link between the diagnosed processes and the peak sea level
The manuscript identifies baroclinic currents, internal-wave-like variability, and a mean density-front contribution, but it does not clearly show how these combine to explain the 7 cm peak difference at Venice.
A more explicit budget, or at least a clearer estimate of the sea-level signal associated with the internal seiche, would strengthen the paper substantially.
5. Scope and framing
This is presented as a forecasting study, but it is based on a single event and a single initialisation. It reads more like a case study or hindcast analysis than a forecast evaluation.
The framing should be toned down accordingly, especially where forecast skill or predictability is implied.
6. Robustness
Because the analysis is based on one event only, it is difficult to judge how robust the reported differences are to initial conditions or modest changes in setup. I do not think an ensemble is essential, but the paper should be clearer about the limits of the analysis.