2023/10/20 Storms Babet & Aline
Strong winds in storms Babet & Aline likely strengthened by both human-driven climate change and natural variability
Press Summary (First published 2023/10/22, updated 2023/11/22)
Storms similar to Babet & Aline are 3 hPa to 5 hPa deeper, 5 km/h to 15 km/h windier and 5-20 mm/day wetter on the Atlantic coasts in the present than they would have been in the past.
Storms Babet &Aline were somewhat uncommon events.
The Surface Pressure Anomalies show a large negative (cyclonic) anomaly over Western Europe. This configuration, typical of Atlantic extratropical storms, is prone to advect wet and warm air from Western Africa to central Europe contributing to strong winds. Temperature data show warm anomalies over a large part of the European continent during the storms. Precipitation Data show high amounts of precipitaiton over Northern Spain, Scotland, the Benelux and the Alps. Windspeed data shows large areas of Europe with wind above 50 km/h locally peaking to 100 km/h.
The Coupled Model Intercomparison Project (CMIP) phases 3, 5, and 6 generally agree on the spatial signature of the projected changes in storminess in the North Atlantic (Harvey et al., 2020, Priestley et al, 2020). Summers are expected to see reduced storm activity, while winters should bring increased storms in the British Isles and reduced storms in the Mediterranean and Norwegian seas. According to the IPCC AR6 report, changes in the dynamical intensity (e.g. wind speeds) of storms will be small (medium confidence), “although changes in the location of storm tracks can lead to substantial changes in local extreme wind speeds ”. The IPCC report further states that “there is high confidence that the precipitation associated with extratropical cyclones will increase in the future”. Ginesta et al 2023 found that Storm Alex, similar in the meteorological structure, impacts and timing to Storm Aline, has shown an increase in persistence, as well as higher levels of precipitation and stronger wind speeds in the recent period compared to the past.
Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For this event we have medium-high confidence in the robustness of our approach given the available climate data, as the event is similar to other past events in the data record.
We analyse here (see Methodology for more details) how events similar to 2023 Babet & Aline storms have changed in the present (2001–2022) compared to what they would have looked like if they had occurred in the past (1979–2000) in the region [-20°E 20°E 30°N 60°N]. Surface pressure changes indicate that storms resembling Babet & Aline exhibit pressure anomalies deeper by 3 to 5 hPa in the present than in the past. Additionally, changes in Windspeed changes reveal that these storms are now 5-18 mm/day wetter 5 to 20 km/h windier on the Altantic European coasts in the present than in the past. A similar signal is found for the analysis in the urban areas of Cork (Ireland), Glasgow (Scotland) and Oristano (Sardinia, Italy). These cities are getting windier and wetter in the present than in the past during storms similar to Babet & Aline. We also note that Similar Past Events have become more common in the months of October and November, while they previously occurred in the extended autumn season. Among similar past events we find indeed Alex storm, which caused widespread destruction in South of France and Northern Italy.
Based on the above, we conclude that windstorms similar to Babet & Aline are 3 hPa to 5 hPa deeper, 5 km/h to 15 km/h windier and 5-20 mm/day wetter on the Atlantic coasts in the present than they would have been in the past. We interpret Storms Babet & Aline as unusual events whose characteristics can mostly be ascribed to human driven climate change.
Mireia Ginesta, IPSL-CNRS, France 📨firstname.lastname@example.org 🗣️Catalan, Spanish, English
Davide Faranda, IPSL-CNRS, France 📨email@example.com 🗣️French, Italian, English
Additional Information : Complete Output of the Analysis
NB1: The following output is specifically intended for scientists and contain details that are fully understandable only by reading the methodology described in Faranda, D., Bourdin, S., Ginesta, M., Krouma, M., Noyelle, R., Pons, F., Yiou, P., and Messori, G.: A climate-change attribution retrospective of some impactful weather extremes of 2021, Weather Clim. Dynam., 3, 1311–1340, https://doi.org/10.5194/wcd-3-1311-2022, 2022.
NB2: Colorscales may vary from the ClimaMeter figure presented above.
The figure shows the average of surface pressure anomaly (msl) (a), average 2-meter temperatures anomalies (t2m) (e), cumulated total precipitation (tp) (i), and average wind-speed (wspd) in the period of the event. Average of the surface pressure analogs found in the counterfactual [1979-2000] (b) and factual periods [2001-2022] (c), along with corresponding 2-meter temperatures (f, g), cumulated precipitation (j, k), and wind speed (n, o). Changes between present and past analogues are presented for surface pressure ∆slp (d), 2 meter temperatures ∆t2m (h), total precipitation ∆tp (i), and windspeed ∆wspd (p): color-filled areas indicate significant anomalies with respect to the bootstrap procedure. Violin plots for past (blue) and present (orange) periods for Quality Q analogs (q), Predictability Index D (r), Persistence Index Θ (s), and distribution of analogs in each month (t). Violin plots for past (blue) and present (orange) periods for ENSO (u), AMO (v) and PDO (w). Number of the Analogues occurring in each subperiod (blue) and linear trend (black). Values for the peak day of the extreme event are marked by a blue dot. Horizontal bars in panels (q,r,s,u,v,w) correspond to the mean (black) and median (red) of the distributions.