Past evolution of western Europe large-scale circulation and link to precipitation trend in the northern French Alps

Blanc, Antoine; Blanchet, Juliette; Creutin, Jean‐Dominique

doi:10.5194/wcd-3-231-2022

Cited by 6 publications

(5 citation statements)

References 53 publications

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“…(2022a) or even new circulation descriptors reflecting for instance the latitude of zonal winds. However circulation alone cannot fully explain trends in extreme precipitation, as observed for past trends in the northern French Alps (Blanc et al., 2022b). This is also confirmed by looking at the distribution of precipitation in the PE class simulated by CNRM‐CM6‐1.…”

Section: Discussionmentioning

confidence: 97%

“…Both the singularity and the MPD were shown to explain a significant part of precipitation variability in the northern French Alps, as well as to characterize the atmospheric circulations driving extreme precipitation in the region (Blanc et al., 2021, 2022a, 2022b).…”

Section: Methodsmentioning

confidence: 99%

“…However, our method requires to know which LSCs characteristics are likely to drive extreme precipitation in a given region. The choice for considering the singularity and the hollowness of geopotential shapes in this article follows previous studies (Blanc et al, 2022a(Blanc et al, , 2022b but it is probably not relevant everywhere. Application of the method to other regions or other variables is thus not immediate.…”

Section: Generalization Of the Approachmentioning

confidence: 99%

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Will Future Southwestern Europe Large‐Scale Circulations Resemble Past Circulations? A Focus on the Circulations Driving Extreme Precipitation in the Northern French Alps

et al. 2023

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Section: Discussionmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

Section: Generalization Of the Approachmentioning

confidence: 99%

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Will Future Southwestern Europe Large‐Scale Circulations Resemble Past Circulations? A Focus on the Circulations Driving Extreme Precipitation in the Northern French Alps

et al. 2023

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“…The approach uses three basic variables that define the circulation features at the surface over a given window: the direction of mean flow, the strength of mean flow and the vorticity. Following previous works of Raynaud et al (2017), Blanc et al (2022a) and Blanc et al (2022b) relating precipitation to surface weather and atmospheric analogues, we consider here the Western Europe window of Figure 2 and, thus, we adapt the method of Jones et al (1993) to our region of study; we provide details in Appendix A.…”

Section: Main Types Of Atmospheric Circulationmentioning

confidence: 99%

Linking torrential events in the Northern French Alps to regional and local atmospheric conditions

Blanchet

Reverdy

Blanc

et al. 2023

Preprint

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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).

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“…The approach uses three basic variables that define the circulation features at the surface over a given window: the direction of mean flow, the strength of mean flow and the vorticity. Following previous works by Raynaud et al (2017), Blanc et al (2022a) and Blanc et al (2022b) relating precipitation to surface weather and atmospheric analogues, we consider here the Western Europe window of Figure 2 (see the Lamb points) and, thus, we adapt the method of Jones et al (1993) to our region of study; we provide details in Appendix A.…”

Section: Weather Type Classificationmentioning

confidence: 99%

Linking torrential events in the Northern French Alps to regional and local driving atmospheric conditions

Blanchet,

Reverdy,

Blanc

et al. 2023

Preprint

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Abstract. The Alpine region is strongly affected by torrential floods, sometimes leading to severe negative impacts on society, economy, and the environment. Understanding such natural hazards and their drivers is essential to mitigate related risks. In this article we propose a statistical method based on a mere discriminative index to objectively isolate the atmospheric variables associated with torrential events with long return periods. The method is applied to the Grenoble Metropolitan area in the Northern French Alps using a list of dates of damaging torrential events 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. Two spatial scales are considered – a local scale (the Grenoble conurbation) and a regional scale (the French Alps) –, in order to study the spatial variability of the atmospheric signature. 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. The results show that a simple discriminative index – the so-called silhouette index – is able 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. All atmospheric variables turn out to be less discriminant for torrential events before 1950 according to 20CRv2c – this is likely linked to 20CRv2c issues over the remote past. For the post-1950 period, in the North-West class – which is both the most frequent class generating torrential events and the best discriminated – humidity and particularly humidity transport (IVT) plays the greatest role. In the Southeast-Southwest class – the second most frequent class generating torrential events–, 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. The gain in prediction provided by the discriminant variables is substantial. 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). Although the results are likely to be region-dependent worldwide, the methodology used in this article is generic and could be used elsewhere to find the most discriminating atmospheric variables – provided a list of flooding dates is available. It is also remarkable that the same atmospheric variables with the same discriminative power are found whether we consider them at local or regional scale. This means that, although torrential events are triggered by very local precipitation, the atmospheric signature for such events is actually much wider. Thus, although the present study applies to a small region of the Northern French Alps, it is reasonable to presume that similar results would apply to other torrential catchments in the French Alps.

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Past evolution of western Europe large-scale circulation and link to precipitation trend in the northern French Alps

Cited by 6 publications

References 53 publications

Will Future Southwestern Europe Large‐Scale Circulations Resemble Past Circulations? A Focus on the Circulations Driving Extreme Precipitation in the Northern French Alps

Will Future Southwestern Europe Large‐Scale Circulations Resemble Past Circulations? A Focus on the Circulations Driving Extreme Precipitation in the Northern French Alps

Linking torrential events in the Northern French Alps to regional and local atmospheric conditions

Linking torrential events in the Northern French Alps to regional and local driving atmospheric conditions

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