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. 

Hundreds of people lost their lives in the floods and more than 700,000 were affected by the floods across all countries due to infrastructure damages, school closures, lost livestock and thousands of hectares of damaged crops. 

Researchers from Kenya, the Netherlands, Germany, Sweden, Denmark and the United Kingdom collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of the rainfall that led to the severe flooding in the most affected region. 

The impacts were most severe in the region around Lake Tanganyika, Lake Victoria, the central Highlands (including Nairobi), southeast lowlands of  Kenya and coastal Tanzania between the end of March and most of April. To capture this event we looked at the 30-day maximum accumulated rainfall during the long rains (March to May) in the area outlined in red in Figure 1. 

Main findings

• Countries in East Africa have been facing disaster after disaster, including prolonged drought between 2020-23,  and multiple episodes of torrential rainfall leading to severe flooding. These disasters combine to create a complex humanitarian emergency that includes displacement, infrastructure loss, food insecurity, health risks, disrupted livelihoods, and overall weakened resilience. 
• Rapid urbanisation in cities across East Africa is amplifying flood risks, especially in large informal areas that are located on flood-prone land, lack adequate structural protections from the rains, and whose residents lack resources to recover and rebuild. Land-use changes, including deforestation and conversion to agricultural land are also occurring to different degrees in each of the countries studied, adding to flood risk. 
• The East African long rains were observed to show a drying trend towards the end of the 20th century, while climate models projected an increase in heavy rainfall with global warming. While this so-called East Africa Paradox is not as pronounced anymore, with observed precipitation increasing and a new generation of climate models showing weaker or no wettening trend, interpreting observations and climate models is still challenging in this region. 
• The observations, independent of the exact region and data product, do not show a long term trend, but instead a drying trend towards the end of 20th century up until around 2008 and a wettening in the last 15 years. Regardless of whether the recent recovery is being enhanced by human-induced climate change, the increased precipitation does bring an increased risk of flooding to the region.
• To understand if human-induced climate change is indeed playing a role, we also assess whether there are wettening or drying trends in the region for the long rains in climate models. While the trends are not statistically significant, they do show a wettening. On average, an event like this has become about twice as likely and 5% more intense in today’s climate, representing the effect of 1.2C of global warming. 
• Looking at the future, for a climate 2°C warmer than in preindustrial times, models suggest that rainfall intensity and likelihood will increase further.  
• We also examined whether the current phase of the El Nino Southern Oscillation or the Indian Ocean Dipole played a role in the intensity and likelihood of the wet March-May rainy season. Both modes of natural climate variability have been found to exhibit a negligible influence on the 2024 long rains in the study region. 
• Taking these findings and the known physical relationship that heavy rainfall is expected to increase in a warming world, we conclude that the observed increase in rainfall in the region over the last 15 years is in part driven by human-induced climate change. 
• Therefore, investing in flood resilience with future warming is paramount. 
• While early warning systems in each of the countries exist and warn of extreme rainfall, there is room to expand the action taken based on warnings to adequately protect people from the rainfall impacts. Social protection programs can fill gaps in instances where it’s not possible to avoid all impacts, in order to help people recover their assets and livelihoods after the disaster. 
• Disaster preparedness policies, flood preparedness and protection infrastructure, and early warning systems that are in place across Kenya, Tanzania and Burundi are all steps in the right direction, but must be integrated and implemented at scale in order to reduce impacts.

Heatwaves are arguably the deadliest type of extreme weather event and while the death toll is often underreported and not known until months after the event, a surge in hospital admissions and deaths were reported from the Gabriel Touré hospital in Bamako, Mali between 1-4 April (Bahati, 2024).

The hospital recorded 102 deaths over the four-day period, which is significantly more than expected – in April 2023, the hospital recorded 130 deaths over the entire month (JolibaFM, 2024). While statistics for the cause of death have not been reported, around half were over the age of 60, and the hospital reports that heat likely played a role in many of the deaths. Furthermore, up to 44 bodies were buried in one cemetery in Bamako on Friday 5 April after the weekly service (DW 2024).

Scientists from Mali, Burkina Faso, Mozambique, the Netherlands, Sweden, the United States and the United Kingdom collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of the extreme heat across the Sahel. Our analysis focuses in detail on the countries that had the highest temperatures, especially also over night and the large reported death toll: The southern part of Mali and Burkina Faso (fig. 1a). Here we look at the 5-day maximum and minimum temperatures over the March to May season and in April respectively. In addition we analyse the 5-day maximum temperatures in March to May over a larger
region (fig. 1b; 10 to 17°N, 16W to 20°E) encompassing the most affected parts of Senegal, Guinea, Mali, Burkina Faso, Niger, Nigeria and Chad.

Main Findings

● While Burkina Faso and Mali are both countries with populations that are acclimated to high temperatures, the length and severity of this heatwave made it difficult for people to cope, as evidenced by the reported increased hospitalisations and deaths. Heatwaves are amongst the deadliest natural hazards with thousands of people dying from heat-related causes each year
and many more suffering other severe health and livelihood consequences. Many places lack good record keeping of heat-related deaths, therefore currently available figures are likely an underestimate.
● This heatwave coincided with Ramadan (fasting) and power cuts, which compounded the risk for vulnerable groups and even those not traditionally considered vulnerable. Even minimum temperatures, overnight, remained relatively high, making it so that people did not get a break from the heat. The power cuts further made it difficult for those who did have access to
mechanical cooling to use it, thus reducing their coping capacity.
● Even in today’s climate, that has warmed by 1.2°C since pre-industrial times due to human activities, the extreme heat observed over the Mali/Burkina Faso region is still rare. While the daily temperatures were extreme, with a return time of about 100 years, the 5-day maximum temperatures were particularly unusual with a return time of 200 years. Minimum temperatures were less extreme but still rare with a return time of 20 years over Mali/Burkina Faso. For the Sahel region the return time of the 5-day maximum temperatures are 30 years.
● To estimate the influence that human-caused climate change has had on the extreme heat since the climate was 1.2°C cooler, we combine climate models with observations. Observations and models both show that heatwaves with the magnitude observed in March and April 2024 in the region would have been impossible to occur without the global warming of 1.2°C to date.
● Extreme 5-day maximum heat as rare as the observed event over Mali/Burkina Faso would have been 1.5 °C cooler and 1.4 °C cooler over the larger Sahel region if humans had not warmed the planet by burning fossil fuels. For minimum temperatures over Mali/Burkina Faso the change in intensity is even larger: in a 1.2°C cooler climate the nighttime temperatures would have been 2°C cooler.

● These trends will continue with future warming. Over Mali/Burkina Faso a heatwave like the observed event would be another 1°C hotter in a 0.8°C warmer world (2°C global warming since pre-industrial times). An event of the same magnitude as observed in 2024 would then not be very rare anymore but occur 10-times more frequent than in today’s climate.
● We also assessed whether the current El Niño event had an influence on the extreme temperatures and found that while there is some contribution it is small compared to human-induced climate change, explaining about 0.2°C of the observed 5-day heat event.
● Rapid urbanization and loss of green spaces in cities such as Bamako and Ouagadougou have increased the urban heat island effect. Coupled with high vulnerability, this highlights the need for sustainable urban planning that integrates green spaces, and building designs that account for high temperatures.
● Critical infrastructure such as electricity, water, and healthcare systems needs to be strengthened to adapt to the increasing frequency and intensity of extreme heat, requiring increased investment to ensure reliable access and service delivery.

Years with a positive phase of the El Niño Southern Oscillation (ENSO) have been associated with droughts in that region in the past, but impacts have not been homogenous, with some El Niño events leading to droughts while others did not. This is because other climate modes of variability such as
Indian Ocean Dipole and Subtropical Indian Ocean Dipole play a critical role in the rainfall amount and distribution over the affected region.

Furthermore, human-induced climate change has been found to increase aridity in some regions in Southeastern Africa, but studies encompassing the countries affected by the 2024 drought, which has been reported to be the worst on record in parts of Zambia and Zimbabwe, are sparse and often focus on much larger regional averages.

Scientists from Zambia, Botswana, Kenya, Mozambique, South Africa, the Netherlands, Sweden, and the United Kingdom collaborated to assess to what extent the 2024 ENSO state as well as human-induced climate change altered the likelihood and intensity of the low rainfall that led to drought, as well as the increase in evaporation due to climate change, exacerbating drought severity.

We focus the analysis on the most affected countries, Zimbabwe, Botswana, Zambia and Mozambique but only the Southern parts for the last two countries to study a climatologically homogeneous region. The temporal focus is December to February (DJF), the peak of the rainy season in the region.

Main findings

● Reliance on rain-fed subsistence crop production and drought-sensitive water sources result in chronic high vulnerability to rainfall anomalies, and limited coping capacity.
● Multiple drivers contributed to the currently high, and rising, food insecurity and malnutrition levels including several years with high food prices, ongoing recovery from floods, as well as agricultural pests and diseases.
● High deforestation rates are a major driver of environmental degradation across the countries, exacerbating risk and impacts associated with drought.
● Using four different observational data products we find that droughts such as this one are expected to happen in today’s climate about once every decade. However, when we consider the effect of El Niño, we find that these droughts are twice as likely to occur in El Niño years. Thus El Nino is a key driver of the 2024 event.
● To analyse the role of human-induced climate change we first looked at the relationship between global warming and rainfall anomalies in observation-based data products. We find that as global temperatures increase, rainfall in DJF also increases. This means that in the current climate, with 1.2ºC warming, droughts such as this one are actually less likely than in a cooler, pre-industrial climate. This finding is consistent with previous studies that show wetter conditions in DJF that contrast with drying in the region earlier in the season, between the months of September and November).
● To further evaluate the role of climate change in the current drought we combined the observations with climate models. The models that passed the model evaluation do not show a significant relationship between rainfall and global warming levels with increasing global temperatures.
● The analysis also indicates that with further global warming of up to 2ºC there will be no significant change in the likelihood of low rainfall in DJF as observed in the region in early 2024.
● Repeating all the analysis for the effective precipitation, taking evapotranspiration into account and only looking at water that is actually available for plants, we find very similar results.
● In summary, our analyses show that El Nino significantly increases the likelihood of such a drought to occur, while climate change did not emerge as the significant driver influencing assessed drought in the affected countries.
● As El Nino events will continue to occur in a warming climate it is important to increase resilience to droughts that will continue to occur frequently.
● Countries in the region have varying levels of development, infrastructure, and governance systems that impact their ability to respond to the drought. For example Botswana is relatively more developed than the other countries in the study and its economy and people are less reliant on rain-fed agriculture, resulting in fewer impacts.
● Maintaining robust traditional land governance systems with appropriate integration into modern frameworks appears crucial for sustainable land management and reducing drought vulnerability to southern Africa.
● Effective early warning systems, anticipatory action, and coordinated emergency response efforts are in place, and could be further strengthened by commitments for shock responsive social protection systems.

Humid heatwaves are known to be particularly dangerous. While meteorological organisations in Ghana and Nigeria issued warnings, few heat-related impacts were reported by the media and government organisations across the Guinea zone. In February, West Africa was hit by an unusually intense early season heatwave, with temperatures not normally seen until March or April. The most severe heat occurred from February 11-15 with temperatures above 40°C. In Nigeria, doctors reported an increase in patients presenting for heat-related illness, people complained of poor sleep due to hot nights and the national meteorological agency issued several warnings about the heat. In Ghana, the national meteorological agency also warned people to prepare for dangerous temperatures. The heat occurred during the finals of the Africa Cup of Nations (AFCON) football tournament in Côte d’Ivoire. Due to the hot and humid conditions, additional ‘cooling breaks’ were taken during the matches so players could rehydrate.

Scientists from Nigeria, Burkina Faso, Switzerland, Sweden, South Africa, The Netherlands, Germany, the UK and the US collaborated to assess whether and to what extent human-induced climate change has modified the likelihood and intensity of this February humid heatwave. The team used published peer-reviewed methods to analyse the event. To account for the humidity, which increases the impacts of heat on the human body, the team analysed the Heat Index, which accounts for both daily maximum temperatures and relative humidity. The event was defined as the annual (Jul-Jun) maximum 5-day averaged Heat Index in a region near the southern coast of West Africa (see Figure 1).

● Very limited impact data are available across the studied area. It does not mean there were no impacts but suggests limited awareness about heat risks. To reduce heat-related morbidity and mortality in southern West Africa, there is an urgent need for improved monitoring and research on the impacts and risks associated with heat waves.
● Rapid, unplanned urbanization with about half of the urban residents on average living in informal housing renders a considerable portion of the region’s population highly exposed and vulnerable to extreme heat. Widespread energy deficiency and limited access to water, sanitation, and hygiene (WaSH) and healthcare services further aggravate heat-related health risks as individuals are left with very limited options for individual coping strategies, such as air conditioning.
● In January and February, the heat affected the African Cup of Nations football games in Côte d’Ivoire. Two-minute cooling breaks were proactively introduced at the 30th and 75th minutes of many matches, with provisions for additional breaks during the sessions so players could rehydrate. The study did not identify evidence of mandatory cooling breaks for outdoor workers across the region who are highly vulnerable to heatwaves
● In southern West Africa, the 5-day humid heat maximum usually occurs in March or April. The humid heat measured using the heat index was record high in February in terms of the annual average (usually occurring in March/April) but even more when considering it happened as early as in February.
● The datasets based on observations characterise the area’s average 5-day humid heat as a 1-in-10 year event in today’s climate.
● To estimate the influence of human-caused climate change on this excessive humid heat we use a combination of climate models and observations. We find that because of human-induced climate change, the area-averaged heat index is in today’s world about 4°C higher in today’s 1.2°C warmer climate. Also, such humid heat has become much more likely, it is at least 10 times more likely in today’s world.
● At global mean temperatures of 2°C above pre-industrial levels, humid heat such as observed this year is projected to be about another 1.2°C to 3.4°C warmer and about another factor of 3 to 10 times more likely, meaning similar events will occur about once every two years.
● Despite limited data and research, in recent years, there is an increase in awareness of heat-related risks by national weather services (e.g. Nigeria) and city authorities (e.g. Freetown, Sierra Leone). Further improvements and investments are needed, such as extending heat warnings to hot days outside of the typically hot season. This is especially urgent as the planet continues to heat, causing prolonged and hotter heat seasons.
● However, across the countries analysed, many do not appear to have carried out planning for heat extremes. Major investment is needed in Africa to build resilience to dangerous heat. The UN has estimated that the cost of adaptation for developing countries is between US$215-$387 billion per year this decade. However, rich countries haven’t yet met the promises they have made to help developing countries become more resilient to the growing risks of climate change. In addition, these commitments fall drastically short of the finance required – in 2021, the global community spent just US$21 billion to help developing countries adapt to climate
change

The ongoing floods are hitting vulnerable communities that were already suffering from loss of livelihoods, malnutrition and hunger due to livestock deaths and crop failure in the context of the drought that only ended with the ongoing heavy rains. The floods led to more than 300 reported deaths so far and displaced over a million people in Kenya and Somalia alone. 

Researchers from Kenya, Ethiopia, South Africa, 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. 

Across the region several individual heavy rainfall events of varying length led to flash flooding as well as several rivers bursting their banks. To capture this range of flood-inducing rainfall processes, we analysed different lengths of cumulative rainfall. However the results are very similar independent of whether investigating a few days or a whole month. Thus we choose maximum 30-day mean rainfall over OND as the event definition. The study region is outlined in black in Fig. 1, and has a fairly homogenous climate with a distinct long (March to May) and short rainy season (OND), characterised by arid and semi-arid climate. 

Main Findings

• Historical drought and recent flooding compounded exposure and vulnerability of populations and population sub groups to severity of flood-related impacts  
• From the end of October throughout the rainy season up till now rainfall over the region was very heavy, leading to exceptional amounts of precipitation accumulated on several timescales from 1-day to 30-day, with 2023 showing either highest or second highest events on record. 
• The OND rainy season is known to be influenced by modes of natural variability, including the El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) as the dominant modes of variability. Both ENSO and IOD are in a positive phase which has been shown to increase the likelihood of heavy rainfall in the wider Horn of Africa OND season.
• For the region analysed in this study we find no significant role of ENSO but a significant influence of the IOD. In the current IOD phase and under the current climate conditions, an event of this magnitude is expected to happen more often than under IOD neutral conditions, with a return period of approximately 1 in 5. In other words, we would expect to see such an event occurring in every 5th positive IOD-year in the present climate. Overall, taking into account the recent behaviour of the positive IOD, the event would have a return period of around 1 in 40 years in the current climate, that has been warmed by 1.2C due to the burning of fossil fuels. 
• Based on three observation-based data products we find that due to the effect of the IOD, the intensity of the rainfall this OND season was about twice what would be expected in a neutral IOD year. Similarly we find that due to the warming of 1.2C up till now, the magnitude of rainfall has also approximately doubled. Thus, climate change and a positive IOD contributed approximately equally to the magnitude of the event.
• It is important to highlight however that IOD is a natural phenomenon that oscillates between neutral, positive and negative phases while the effect of human-induced climate change will continue to increase until the burning of fossil fuels is stopped.  
• Only very few models exhibit a correlation between the IOD and OND rainfall. These models also show an increase in the intensity attributable to human-induced climate change but smaller than the observations. Combining both observations and models, we estimate that human-induced climate change increased the intensity of OND rainfall by up to a factor of two. 
• Due to the low number of models and short observed records we have however low confidence in this quantification, but very high confidence in the overall result that climate change increased the intensity of heavy rainfall in the OND season in the Horn of Africa.
• Longstanding land use land cover (LULC) practices, unsustainable land management in the face of rapid urbanisation, as well as systemic challenges in implementing early warning early action in vulnerable communities increased community-level exposure to extreme rainfall and subsequent flooding. 
• Despite existing anticipatory action mechanisms and Early Warning Early Action (EWEA) protocols, the increasing severity and frequency of extreme weather events in the Horn of Africa can potentially overwhelm the operational response capacity of government, development, and humanitarian actors. Ongoing review and reinforcement of response, preparedness, and social protection systems will create a better prepared Horn of Africa. 

Scientists from Madagascar, South Africa, Denmark, the Netherlands and the UK collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of hot Octobers in Madagascar and the warmest 7-day maximum and minimum temperatures in Antananarivo during the month (fig 1), using published peer-reviewed methods. Drawing from studies in similar contexts and other regions in the world they also assessed what the impacts on humans and ecosystems in the region likely are.

Main findings

● Heatwaves in all regions of sub-saharan Africa are dramatically underreported leading to little awareness about the dangers of extreme heat. Heat-related mortality is estimated to increase by a factor of four by 2080, unless required investments to adaptation are made.
● South Madagascar is particularly vulnerable to impacts of heatwaves, as food and agricultural systems are likely to collapse under high temperatures and compounding drought conditions and frequent, highly destructive cyclones. Extremely dry air during heatwaves, including the nights, results in difficulty to breathe, and children are reported to be the worst affected with an overall high heat-related mortality.
● Using gridded observational products the very warm October is approximately a 1 in 100 year event in today’s climate, while the extreme warm 7-day maximum and minimum temperatures are less rare, estimated to be a 1 in 25 and 1 in 20 year event respectively.
● To estimate the influence of human-caused climate change on this extreme heat we use a combination of climate models and the observations. We find that because of human-induced climate change the event would have been approx. 1 to 2 °C cooler for all three event definitions had humans not warmed the planet by burning fossil fuels.
● Due to the strong trend the change in likelihood is very large: it has increased by at least 100 times for October mean and 7-day minimum temperatures and by at least 10 times for the 7-day maximum temperatures.
● Unless the world rapidly stops burning fossil fuels, these events will become more common in the future. In a world 2°C warmer than preindustrial, events like these would no longer be rare but occur up to 3 times per decade.
● In Madagascar, less than half of the population has access to electricity and clean water, making most common coping strategies in extreme heat inaccessible to a large part of the population. Linked to the lack of clean water is one of the lowest child survival rates in the world. With very young children being particularly vulnerable to extreme heat these young lives are even more endangered.
● A high degree of informal settlements and unplanned urbanisation have resulted in large parts of the population particularly vulnerable to heat exposure. Factors like urban poverty, large workforce in informal economies, and loss of productivity/income during hot days result in compounding vulnerabilities.
● There are no heat action plans, early actions protocols, or comprehensive early warning systems, indicating an overall limited preparedness for heat waves. Investments in extreme heat forecasting, warning, and response capabilities are the most urgent requirements for Madagascar to better adapt to a warming world.

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.

Historic and current weather observations in the region are sparse, making it difficult to identify the exact dates and spatial extension of the heavy rainfall. Satellite observations and reanalysis also show very different magnitudes of rainfall around the time of the reported damages but also very different locations of the centre of maximum rainfall (see fig. 1 and fig. 2). 

Researchers from Rwanda, the Democratic Republic of Congo, Kenya, 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 and landslides. Due to the data limitations it is not possible to assess the spatial or temporal extent of the rainfall that led to the flooding, thus a formal attribution study is not possible and the role of climate change cannot be assessed. Given the large humanitarian impacts as well as the importance of drivers of vulnerability there is a huge need to improve data collection and accessibility in this area, as well as research capacity to improve preparedness in a region that is projected to experience more heavy rainfall with increasing global warming. 

Main findings

• We urgently need robust climate data and research in this highly vulnerable region. The scarcity and inaccessibility of meteorological data, as well as inadequate performance of climate models meant we couldn’t confidently evaluate the role of climate change in the rainfall that led to flooding. This limitation applies also to information on the impact, vulnerability, and exposure of people to heavy rainfall, a critical gap that has been highlighted by numerous studies. 
• The death toll and destruction from the floods in South Kivu, DRC and western Rwanda was extreme, and reflects the high vulnerability and exposure of people to flooding in this region. 
• The history of conflict in the region and instability has contributed to underdevelopment and a lack of basic services and infrastructure. The combination of protracted conflict, displacement, under-development, poverty and land degradation, creates a recipe for disaster when an extreme weather event strikes, making it more difficult for people to cope and bounce back from the disaster.
• The conflict and violent clashes between state and non-state groups have led to large-scale displacement in South Kivu, DRC and western Rwanda in 2023, with displaced populations being more susceptible to flood and landslide impacts due to their living conditions (e.g. temporary shelters) and precarious situation. The floods further displaced thousands of people, destroyed water, sanitation and hygiene infrastructure, damaged agricultural fields leading to increased risk of food insecurity, waterborne illnesses and protection issues after the initial recovery phase ends. 
• Deforestation in order to clear land for settlements, agriculture, and mining, has resulted in widespread soil erosion around Lake Kivu, contributing to an increasing  risk of landslides. There is a lack of capacity of the government to enforce limits or regulation on land degrading practices. 
• While the DRC’s mineral reserves are critical for global manufacturing and the transition to a low carbon economy and its forests act as a key carbon sink for the world’s carbon polluters, the country continues to suffer from the impacts of extreme weather which are amplified by mining activities that contribute to land and water degradation, labour abuses, and conflict.
• We examined three different combinations of spatial and temporal extent to look at heavy rainfall events in the region of the floods to see whether there are trends in either of these in the different available data products. In different datasets there are trends in seasonal and short term heavy rain in both directions (increases and decreases), as well as data showing no trend. 
• Climate models show no significant trends in heavy precipitation over the region since the preindustrial climate, but an increase in short term heavy rainfall for a 0.8C warmer world (2C global warming). However, this is no indication that there is no trend, as the uncertainty is very high. 
• The increase in heavy precipitation with future warming is in line with projections from the IPCC over the whole of central and eastern Africa, which also show an increase in heavy rainfall.
• While the scarcity of data does not allow us to draw any conclusions on the role of climate change in the floods today, the potential for a further increase in heavy rainfall in this flood and landslide prone area highlights an urgent need to reduce vulnerability 
• Better observations, improved access to meteorological data and more research are urgently needed in the region to improve early warning systems. 

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).

Main findings

• Heatwaves are amongst the deadliest natural hazards with thousands of people dying from heat-related causes each year. However, the full impact of a heatwave is often not known until weeks or months afterwards, once death certificates are collected, or scientists can analyse excess deaths. Many places lack good record keeping of heat-related deaths, therefore currently available global mortality figures are likely an underestimate.
• Early heatwaves and associated drought conditions also threaten the yield for many crops such as wheat, because it hinders grain filling. This heatwave has come at a critical time for the crop season in the Western Mediterranean countries.
• While Europe and North Africa have experienced heatwaves increasingly frequently over the last years, the recent heat in the Western Mediterranean has been so extreme that it is also a rare event in today’s warmer climate. Our estimate of observed temperatures averaged over 3 days were estimated to have a return period of approximately 400 years (at least 60 years) in the current climate, meaning they have approximately a 0.25% chance of happening in any given year.
• ​​To estimate the influence of human-caused climate change on this extreme heat we combine climate models with the observations. Observations and models both show a strong increase in likelihood and intensity but the change is systematically lower in the models than in the observations. The fact that extreme heat is increasing faster than climate models simulate is a known problem in summer in Western Europe, in all climate models, and is also found here. 
• The combined results, giving an increase in the likelihood of such an event to occur of at least a factor of 100, is therefore likely too conservative. At the same time, a heatwave with a chance of occurrence of 0.25% in any given year (return period of 1-in-400 years) would have been at least 2C cooler in a 1.2°C colder world. 
• This discrepancies between the modelled and observed trends and variability also hinders confidence in projections of the future trends. In a future 0.8°C warmer climate (reaching a global warming of 2C above pre-industrial levels) such a heatwave would be another 1°C hotter, but as above, this is probably a very conservative estimate. 
• Heat-related fatalities have decreased in cities with urban planning for extreme heat. This has proved effective in Spain, and notably in Lisbon, Portugal, where  the urban heat island effect has been reduced through incorporating more green and blue spaces. In addition, early warning systems for heat, simple self-protective behaviours such as drinking enough water, city heat action plans, strong social ties, and improved risk perception have been shown to reduce heat-related health impacts.