Scientists from Italy, the Netherlands, Sweden, the UK, the European Commission and the US used published peer-reviewed methods to assess whether and to what extent climate change influenced the 12.month drought in the two islands (1) Sicily and (2) Sardinia.

There are several ways to characterise a drought: meteorological drought is defined only by low rainfall, while agricultural drought combines rainfall estimates with evapotranspiration or directly measures soil-moisture content. As increased evapotranspiration due to regional warming can play a major role in exacerbating drought impacts, we assess agricultural drought in this study by means of  the Standardised Precipitation Evapotranspiration Index (SPEI), which calculates the difference between rainfall and potential evapotranspiration to estimate the available water. The more negative the SPEI values are, the more severe the drought is classified. Figure 1 shows the SPEI for the 12 months between July 2023 and August 2024 over Italy, and the category it falls in according to the US Global Drought Monitor classification system.  

Main findings

• The main economic activities in Sicily, agriculture and tourism, both strongly depend on water availability. The economic consequences of this drought are thus catastrophic for many in the region and recovery will take time. In Sardinia, agriculture is economically less important, but of high cultural relevance; leading to challenges with water prioritisation for domestic and agricultural use on both islands. 
• Natural ecosystems also suffer. Agricultural expansion, especially in Sicily, has increased water demand, with a decrease of 62ha per year since 1990 in natural ecosystems, including wetlands. 
• In different observational datasets the extreme drought, defined by SPEI12 (fig. 1) is among the most severe droughts since records began. All data agree that this drought is not very rare in Sardinia in today’s climate that has warmed by 1.3°C primarily due to the burning of fossil fuels, with a return period of about 10 years (3 – 93 years). In Sicily, such a drought does not occur very often, with a best estimated return period of around 100 years (10- 200,000 years) in today’s climate. 
• Based on the US Drought Monitoring Classification system, the 1-in-10 year drought over Sardinia which is an ‘extreme’ (D3) drought now would be classified as a ‘severe’ (D2) drought without the effects of climate change, and with further warming would be a more severe ‘extreme’ drought (D3). The rare 1-in-100 year drought over Sicily which is also an ‘extreme’ (D3) drought would be a ‘severe’ (D2) drought without climate change, and with a further 0.7C of warming, will become an ‘exceptional’ drought (D4). For both islands, the likelihood of a drought as defined by SPEI12 from August 2023 to July 2024 has increased by about 50% due to human-induced climate change. 
• To understand the meteorological drivers of these changes in drought, we also assess the individual components making up the drought index, namely rainfall, potential evapotranspiration and temperature. We find that changes in rainfall are small and not statistically significant: on the contrary, both values observed for potential evapotranspiration and temperature as observed this year would have been almost impossible to occur without human-induced climate change. We thus conclude that this increase in drought severity is primarily driven by the very strong increase in extreme temperatures due to human-induced climate change. 
• It has been well-established that climate models tend to underestimate the increase in extreme temperatures in Europe; this in part accounts for the discrepancy between the observed change in drought frequency and intensity and those represented in climate models. 
• Unless the world rapidly stops burning fossil fuels, these events will become even more common in the future. In a world 2°C warmer than preindustrial, which could happen as soon as 2050 without large and rapid reductions in greenhouse gas emissions, droughts like the ones in Sicily and Sardinia will become more frequent. 
• Effective drought risk management in regions such as Sardinia and Sicily requires a sustained focus on long-term preparedness and adaptation. Investing in resilient infrastructure, water conservation strategies, and sustainable resource management is crucial to mitigating the impacts of drought.

The Event 

Attribution studies continue to show that human induced climate change is making heatwaves hotter and deadlier. In many regions, the influence of human induced climate change is so large that temperatures recorded during heatwaves would not be possible without warming caused by the burning of fossil fuels. This includes parts of the US, the Sahel, West Africa, the Philippines and other countries in East Asia  as well as the Mediterranean. We assess how rare the extreme July 2024 heat in the Mediterranean and examine its impacts, focusing on observational data instead of conducting a detailed attribution study, which would likely produce similar results to previous studies. The results are contextualised with findings from our previous attribution studies in the region and global analyses.

Key Messages 

• Heatwaves are the deadliest type of extreme weather, with hundreds of thousands of people dying from heat-related causes each year. The July heatwave caused at least 21 deaths in Morocco after temperatures reached 48°C. However, it is likely there were dozens or hundreds of other heat-related deaths in the countries affected that have not been reported and the full impact of a heatwave is rarely known until months afterwards, once death certificates are collected, or scientists can analyse excess deaths. Many places lack good record-keeping of heat-related deaths, therefore global mortality figures are a significant underestimate.
• In line with past climate projections and IPCC reports, extreme heat events like July 2024 in the Mediterranean are no longer rare events. Similar heatwaves affecting Greece, Italy, Spain, Portugal and Morocco  are now  expected to occur on average about once every 10 years in today’s climate that has been warmed by 1.3°C due to human-induced climate change. 
• Based on the data set ERA5, the extreme temperatures reached in July would have been virtually impossible if humans had not warmed the planet by burning fossil fuels. In addition, the 1 in 10 year extreme July heat would have been 3°C [2.5 – 3.3°C] cooler in a world without climate change. 
• These results are based on observational data and do not include climate models. However, the results are very similar to the studies published  in 2023 that analysed heatwaves in the same region and included climate models. For both the April and e July heatwaves in 2023, we found the events would have been virtually impossible without climate change, but are not rare today. We also found the heatwaves were made 1.7-3.5 ºC hotter when compared to a pre-industrial world. 
• The results for the 2023 events synthesised observations and climate models. However, the models are known to systematically underestimate extreme heat in Europe (van Oldenborgh et al., 2022, Vautard et al., 2023, Schumacher et al., 2024)  meaning the real world changes due to climate change are probably closer to the changes  shown in observations. 
• Furthermore, the previous studies use slightly different temporal and spatial definitions of heat, but the numerical results remain very similar. Given the 2024 event is very similar to the observed changes found in studies published 2023, they are a good indicator of how climate change is affecting extreme heat in the Mediterranean.
• Unless the world rapidly stops burning fossil fuels, these events will become hotter, more frequent and longer-lasting. 
• Studies show that elite Olympic athletes who are exposed to high temperatures and are not acclimated to them may see impacts such as a decline in performance, and increase in heat-related illness, such as heat cramps and exhaustion, having implications for the Paris Olympics that are currently ongoing (de Korte et al., 2021, Griggs et al., 2019). Measures to reduce exposure, ensure adequate hydration and cooling, acclimatisation, and emergency plans can help keep athletes safe during periods of extreme heat.  
• Heat action plans that reduce heat-related deaths are increasingly being implemented across the region, which is encouraging. However, there remains an urgent need for an accelerated roll-out of heat action plans in light of increasing vulnerability driven by the intersecting trends of climate change, population ageing, and urbanisation. Cities are hot-spots for heat risk, so urban planning needs to focus on measures to  reduce the urban heat island effect, such as increasing cooling green and blue spaces. 

All three individual rainfall events caused severe flooding, submerging settlements, leaving thousands homeless and killing at least four people in Bulgaria, six in Spain, seven in Türkiye, and 17 in Greece. Further, 3,958 casualties have been confirmed in the Libyan city of Derna alone, and an additional 170 fatalities elsewhere in the country, while more than 10,000 people are still missing after two major dams broke.

Researchers from Greece, the United States of America, the Netherlands, Germany and the United Kingdom collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of the heavy rainfall that led to the flooding.

To capture the different characteristics of the heavy rainfall and subsequent flooding we focus on two regions to assess the role of climate change: one over Greece, Bulgaria and Türkiye encompassing the region impacted by storm “Daniel” characterised as 4 day maximum rainfall averaged over land in the region 36 to 42.5N and 20 to 28.5 E (red box in Figure 1, 4th to 7th of September). Given that the region receives little rain over the summer (JJAS) but much more in winter, we focus for this event on 4-day max rainfall in the summer season. Secondly, we look at 1-day maximum annual rainfall in a smaller region over Libya (32 to 33N and 20 to 23E, red box in Figure 1, 10th September) where most of the heavy rain fell that led to the devastating flooding in Derna and the surrounding area. We do not assess the role of climate change for the event in Spain due to the fact that the rain fell in less than 24 hours.

Key findings

• The severe flooding in Spain, Greece, Türkiye, Bulgaria and Libya was caused by very heavy rainfall that fell, in the case of Spain in less than 24 hours, whereas it lasted 24 hours in Libya and up to 4 days over Greece and Türkiye.
• For Libya and Spain, we thus evaluate the return period of the annual maximum of 1-day accumulated precipitation; for central Greece, and the larger region defined above the annual maximum of 4-day precipitation. As a summary assessment, we state that the return time for the event in Spain is a 1-in-10 to 1-in-40 year event; for central Greece a 1-in-80 to 1-in-250 year event; for the large GBT region a 1-in-5 to 1-in-10 year event; and over Libya a 1-in-300 to 1-in-600 year event.
• In Libya the event magnitude is far outside that of previously recorded events.
• The uncertainties for the return times are very high and depend on the exact region and dataset chosen. In individual locations they can be very different from the ones shown here.
• To assess the role of climate change we combine observation-based products and climate models and assess changes in the likelihood and intensity of a 1-in-10 year 4-day event over the larger region encompassing Greece, and the parts of Türkiye and Bulgaria that were impacted by flooding, as well as the 1-in-600 year 1-day maximum rainfall event over Libya.
• For the large region including Greece and parts of Bulgaria and Türkiye, we find that human-induced climate change made an event as extreme as the one observed up to 10 times more likely and up to 40% more intense. An event as extreme as the one observed over Libya has become up to 50 times more likely and up to 50% more intense compared to a 1.2C cooler climate.
• The uncertainty in these estimates are high and encompass the possibility of no detectable change, but there are multiple reasons we can be confident that climate change did make the events more likely: from theory we know that an increase in rainfall intensity of around 10%, would be expected given current warming levels, so we could only report that there has been no change if there was a well-known dynamic process counteracting this effect, which there is not. Studies focussing on extreme rainfall with future warming also show an increase in heavy rainfall, rendering it probable that the observed increase in heavy rainfall is indeed a trend due to climate change. For these reasons, we do not give a central estimate of the influence of climate change, as in previous studies, instead giving an upper-bound of the effect.
• In Greece, this has been a summer of extreme heatwaves and fires, including the largest fire ever recorded in the EU, followed by Storm Daniel which devastated the centre of the country. Deforestation and relatively high rates of urbanisation have changed the landscape over time, increasing the number of people and assets exposed to flooding, and reducing stormwater drainage.
• In Libya, the volume of water and overnight timing of the dam failures meant that anyone in the path of the water was at increased risk, not just those who are typically highly vulnerable.
• Ongoing conflict and state fragility in Libya compounded the effects of the flooding, contributing to a lack of maintenance and deterioration of dam infrastructure over time and increasing peoples’ risk and the resulting impacts. The conflict also limits nation-wide adaptation planning and coordination across a range of climate issues facing the country, such as water scarcity, and extreme weather including heat and floods.
• In addition to the lack of maintenance, the Al-Bilad and Abu Mansour dams were built in the 1970s, using relatively short rainfall records, and may not have been designed to withstand a 1-in-300 to 600 year rainfall event. A full after-action review looking at the design criteria of the dams will be required to understand the extent to which the dams’ design, and the lack of subsequent maintenance contributed to the disaster. Even still, catastrophic dam failures and its impacts can be limited through risk reduction protocols that include real-time monitoring of forecasts, water volumes, and warning systems that alert those downstream of possible failures and the need to evacuate.
• While in Libya there was a forecast with a 3-day lead time on the track of Storm Daniel, the impact of that potential rainfall on infrastructure and people was not clearly understood in advance. Further, it is not clear to what extent forecasts and warnings were communicated and received by the general public, or relevant emergency responders. In conjunction with improved emergency management capacity, impact-based forecasts may help to provide a clearer understanding of how the rainfall translates into potential impacts and could lead to improved warnings in the future.
• This disaster also points to the challenge of needing to design and maintain infrastructure for not just the climate of the present or the past, but also the future. In Libya, this means taking into account the long-term decline in average rainfall, and at the same time, the increase in extreme rainfall like this heavy rainfall event; a challenging prospect, especially for a country plagued by crises.