2024/04/01 Easter Extreme Weather in Europe


Extreme weather in Europe during Easter 2024 weekend mostly strengthened by human driven climate change

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Press Summary (First published 2024/04/05)

Event Description

Severe weather phenomena wreak havoc across Europe, from torrential rain in France and Portugal to Saharan dust storms sweeping across Italy. Southern Italy skies were tainted by Saharan sand, casting a surreal yellowish hue, with Sicily and Calabria witnessing an orange-tinged spectacle. This mineral dust, which swept thousands of kilometers, also reaching France, Switzerland, and Germany, compromised air quality, triggering health advisories and warnings against outdoor activities. Even Alpine ski resorts witness an unusual phenomenon as Saharan dust coloured snow with a reddish-brown hue. The pervasive dust storm, emanating from the Sahara, engulfed the central Mediterranean Basin, impacting not only air quality but also visibility. Satellite images captured the vast expanse of the dust cloud, prompting alerts and advisories across affected regions, from Greece to Malta, the dust-laden skies prompt concerns for public health, particularly among vulnerable populations.

Meanwhile, in France, severe flooding compounds the woes, inundating towns and triggering alerts as orange and red flood warnings blanket the region. A town in France finds itself partially submerged following heavy rains and river overflow. Footage reveals the extent of flooding in Montmorillon, with authorities issuing warnings and evacuating homes. The region mobilizes over 100 firefighters and armed forces personnel to aid residents, as emergency calls surge past 350. On March 29th, Portugal Civil Protection recorded 716 incidents due to bad weather, with the majority occurring in the Greater Lisbon and Algarve regions. 

The Surface Pressure Anomalies reveal a significant negative (cyclonic) anomaly over the North Atlantic. This pattern transports warm and moist air towards Europe, also favoring sirocco winds transporting dusts from the Sahara. Temperature data indicate warm anomalies reaching up to +5-10 °C over European continental areas, with negative anomalies around -2 °C over Spain and Portugal. Precipitation data show moderate precipitation amounts over Portugal, Spain, France, and Northern Italy, indicating that heat is coupled with wet conditions, exacerbating the perceived temperature. Windspeed data depict extensive areas of moderate (20-40 km/h) northerly winds.

Climate and Data Background for the Analysis

The IPCC AR6 WG1 highlights climate change impacts compound events in Europe by increasing the probability and frequency of these events. Compound events of dry and hot summers have already increased in Europe, notably in southern, eastern, and western Europe and are projected to increase by mid-century. Compound flooding due to extreme sea level events and extreme precipitation events is observed in Europe, with the probability of such events projected to increase along northern European coasts by the end of the 21st century. The combination of multiple drivers and hazards contributes to societal and environmental risk, leading to compound weather/climate events in Europe. The probability of compound events has likely increased in the past due to human-induced climate change, and this trend is expected to continue with further global warming. Overall, climate change in Europe is leading to an increase in the occurrence of compound events such as dry and hot summers, compound flooding, and other extreme weather events, exacerbating the risks and impacts on ecosystems and societies in the region.

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-low confidence in the robustness of our approach given the available climate data, as the event is unusual in the data record.

ClimaMeter Analysis

We analyze here (see Methodology for more details) how events similar to the Easter Weekend Europe Extreme Weather changed in the present (2001–2023) compared to what they would have looked like if they had occurred in the past (1979–2001) in the region [22°W 25°E 28°N 60°N]. The Surface Pressure Changes show that similar events have become deeper over the Atlantic in the present climate than what they would have been in the past. The Temperature Changes show that similar events produce temperatures in the present climate that are up to 4 °C warmer than what they would have been in the past, over a large area of the region analyzed, mainly Portugal, Spain, France, and Northern Africa. The Precipitation Changes show significant variations up to 13 mm/day (up to 30%) over Portugal, lowering over other regions like the North Atlantic and North Italy. Windspeed Changes indicate up to 10 km/h windier conditions over Southern Mediterranean regions and North Atlantic, favoring transport of dust from the Sahara. We also note that Similar Past Events previously mainly occurred in April and May, while in the present climate they are mostly occurring in February and March. Changes in Urban Areas reveal that Palermo, Lisbon, and Nantes experience 2-4 km/h windier and up to 3 °C warmer conditions in the present compared to the past. Lisbona also experiences increased precipitation (up to 4 mm/day).  

Finally, we find that sources of natural climate variability may have not influenced the event. This suggests that the changes we see in the event compared to the past may be due to human driven climate change.

Conclusion

Based on the above, we conclude that compound events similar to Easter Weekend Europe Extreme Weather are up to 10 hPa deeper and up to 4 °C warmer than previously observed events.  They are up to 13mm/day (up to 30%) wetter over Portugal and 10km/h windier along the Atlantic and Mediterranean coasts. We interpret Easter Weekend Europe Extreme Weather as a very uncommon event which occurs more frequently now in February/March with respect to the past for which human driven climate change played a key role. 

Additional Information : Complete Output of the Analysis

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.