During the last week of April 2023 local temperatures in many regions in Spain, Portugal, Morocco and Algeria were up to 20 degrees higher than normally at this time of year. For Portugal and mainland Spain the national April record was broken by a very large margin, with 36.9°C and 38.8°C respectively measured in the southernmost parts of the countries. In Morocco, several (local) April records have been broken across the country and temperatures exceeded 41°C in some cities such as Sidi-Slimane, Marrakech, Taroudant. Temperatures exceeded 40°C in Algeria on 28 April (Maghnia, Mascara-Ghriss at least).
These record-shattering temperatures came on top of a historical multi-year drought in those regions, exacerbating the impacts of the heat on agriculture which is already threatened by an increasing water scarcity resulting from the combined effect of climate change and water use.
While verified mortality data from the current heatwave are not yet available, we do know that in 2022 heatwaves contributed to nearly 4000 deaths in Spain and over 1000 deaths in Portugal (WHO, 2022). Every year, an average of 262, 250, and 116 people die from heat-related illness in Algeria, Morocco, and Tunisia, respectively (Hajat et al., 2023). In Tunis, a review of all-cause mortality between 2005-2007 found that for every degree Celsius over 31.5C, the daily mortality increased by 2% (Bettaieb et al, 2020). Early season heatwaves tend to be particularly deadly because of a lack of acclimatisation of the population, lower preparedness for heat (e.g. people have not yet brought out fans or A/Cs from storage), and harvesting effects (Gasparrini et al., 2016; Lee et al., 2014).
Scientists from Morocco, France, the Netherlands, the US and the United Kingdom, collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of this early season heatwave.
Using published peer-reviewed methods, we analysed how human-induced climate change altered the likelihood and intensity of the 3-day heatwave event that occurred on 26-28 of April 2023, in the most affected region (see Figure 1, black outline).
Figure 1. ERA5-extended maximum daily temperature anomaly with respect to 1991-2020 averaged over 26-28 April 2023. The black box outlines the study area.