Linking torrential events in the Northern French Alps to regional and local atmospheric conditions
Abstract. In this article we study the atmospheric conditions at the origin of damaging torrential events in the Northern French Alps over the long run, using a database of reported occurrence of damaging torrential flooding in the Grenoble conurbation since 1851. We consider seven atmospheric variables that describe the nature of the air masses involved and the possible triggers of precipitation. Using both 20CRv2c and ERA5 reanalyses, we try to isolate the variables associated with torrential events, by objectively determining which of them differ particularly from the climatology at the dates of torrential events. This analysis is done conditionally on the main types of generating atmospheric circulation derived from Lamb weather classes, namely the North-West, Southeast-Southwest and Barometric Swamp classes. Furthermore, the atmospheric variables are considered over two spatial scales – a local scale (the Grenoble conurbation) and a regional scale (the French Alps), in order to study the spatial variability of the atmospheric signature. The results show that all atmospheric variables are less discriminant for torrential events before 1950 according to 20CRv2c – this is likely more linked to 20CRv2c limitations over the remote past than a consequence of climate change. For the post-1950 period, similar atmospheric signatures are found both at local and regional scales in the North-West and Southeast-Southwest classes and for both reanalyses. In the North-West class – which is the best discriminated – humidity and particularly humidity transport (IVT) plays the greatest role. In the Southeast-Southwest class, instability potential (CAPE) is mostly at play. In the Barometric Swamp class both humidity (PWAT) and instability (CAPE) are discriminant – and even more at the local scale –, showing more mixed situations generating torrential events in this class. In total, depending on the class, torrential events are 4 to 14 times more likely when the respective discriminant variables are extreme (typically above their 0.95-quantile).
Juliette Blanchet et al.
Juliette Blanchet et al.
Juliette Blanchet et al.
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The paper nhess-2022-276 “Linking torrential events in the Northern French Alps to regional and local atmospheric conditions” shows several weakness points and in my opinion should be rejected.
First of all, the title is not appealing: torrential events are “naturally” linked to climatic conditions.
By reading the abstract I guess that the paper is strictly related to the study area. No general conclusions are present, nothing that could be useful in places other than the study area, and this is not in line with the requirements of an international journal. Here, the aim of the paper is not well focused. Even the quotation of climate change seems not strictly related to the analysis performed in the paper.
In the introduction the problem analyzed seems the forecast of torrential events, but at the end of the introduction it seems that the authors work in a simple descriptive way, without finalize the work to something like a classification of severity levels of the effects according to the kind of conditions that triggered them or to something else.
The structure of the paper is not appropriate. In the sections DATA, the authors actually just describe us what they did, and not describe the kind of data required to perform the research. And in METHOD they describe their case study. Then the paper does not supply a clear vision of what someone needs to perform the same research in another geographical area
Moreover, there are no sections describing in a simple way the aim of the paper and the approach followed to reach it. Maybe a flow chart of DATA and STEPS of the METHODOLOGY could help to understand.
Some of the data used are actually NOT described. “20CRv2c (in short 20CR, Compo et al., 2011) covers the period 1851-2014 with a spatial resolution of 2◦. In this article, we use the mean member but results with members 1 and 2 (arbitrarily tested as they are independent) are very similar (not shown). In addition, in order to study the impact of the spatial resolution, the ERA5 reanalysis”. This is simple and clear for you but not for readers that never used this kind of data and could be interested in doing. If I would like to apply the same “approach” in another study area I don’t know what data I need and were could I find them!
Even the information that are obtained from the analysis are sparse all around the sections and it is difficult to identify what can be useful in the practical management of torrential events. Maybe something like a table of the main findings could be useful.
I think that the paper must be completely re-written, putting light more on the scientific question that the paper aims to face and less on the study area (that currently is the focus of the paper). As is the paper does not show interest for an international audience.
Conclusions lack to finalize the results of the research, because not give to the reader the explanation of how these results will help in the management of torrential events or in some other framework.
Further elements in the following:
L 223: 20CR-1 e 20CR-2 have different length but can be compared because in the period 1930-1940 no events were recorded. Could they be comparable even if some events had occurred?