October 30, 2024

expert reaction to flash floods in south-eastern Spain

Scientists comment on flash floods in Valencia, Spain. 

Dr Carola Koenig, a Reader from the Centre for Flood Risk and Resilience, Brunel University of London, said:

“The current devastating flash floods seen in south-eastern Spain bring back memories of the 2021 European floods resulting in nearly 250 deaths. The very high death toll rate of over 180 in Germany raised serious concerns in terms of local warning systems and national, state and local communication lines, as the European Flood Awareness System (EFAS) had repeatedly warned about the adverse weather system over central Europe at the time.

“Spain will now need to investigate also what milestones in terms of flood preparedness and advance disaster management have been missed in view of the over 60 deaths seen already. The cost of Spain’s floods is not yet known but can be expected to be in the billions (the 2021 European flood damage was estimated at $46 billions).

“Unquestionably, climate change is the key contributing factor in these extreme rain events. The Mediterranean has seen the warmest surface water temperature on record with a mean temperature of 28.47°C in mid-August. This facilitates a greater uptake of moisture in the air, resulting in more rain when the atmosphere starts to cool in the autumn. As things stand, Spain needs to embrace itself for continued heavy rain for the next few days.”

Prof Hayley Fowler, Professor of Climate Change Impacts & Director of the Centre for Climate and Environmental Resilience, Newcastle University, said:

“The floods in Valencia are yet another wake up call that our climate is changing rapidly, and that our infrastructure is not designed to deal with these levels of flooding. The evacuation of cities and roads turning into rivers is now commonplace around the world. There is a clear causal link to climate change in the intensification of the extreme rainfall, with extreme rainfall intensifying at a rate of 7% per degree of warming, or more.

“Warmer temperatures cause the intensification of rainfall at all durations, and these large storms, cut off from the jet stream, are able to stagnate in one place and produce huge amounts of rainfall, fuelled by increased moisture and energy from oceans that are record-shatteringly hot. These ‘blocked’ slow-moving storms appear to be becoming more frequent in Europe and are projected to increase further with additional warming. The question is not whether we need to adapt for more of these types of storm, but can we? These storms will become even more intense, causing more flooding, in our warming climate. Reducing greenhouse gas emissions as quickly as possible will reduce the future risks from these events”

Prof Hannah Cloke, Professor of Hydrology, University of Reading, said:

“It is appalling to see so many people dying in floods in Europe, when yet again weather forecasters had predicted extreme rainfall and issued warnings. The tragedy of people dying in cars and being swept away in streets is entirely avoidable if people can be kept away from rising flood water.

“This suggests the system for alerting people to the dangers of floods in Valencia has failed, with fatal consequences. It is clear that people just don’t know what to do when faced with a flood, or when they hear warnings.

“People need to understand that extreme weather warnings for floods are very different from regular weather reports. We need to consider flood warnings totally differently, more like fire alarms or earthquake sirens, and less like the way we browse daily weather forecasts on our phones or on the TV.

“Floods are a risk that have impacted people for all time, but climate change and people moving into harm’s way mean more people are at risk around the world. Politicians and influential people who downplay or ignore these risks are leading us into a dangerous cul-de-sac of inaction. We need to do much more, and do it faster, to adapt to the impacts of climate change that we have already seen, let alone the even worse impacts in the future.”

Dr Marilena Oltmanns, Research Scientist, National Oceanography Centre (NOC), said:

“Higher sea surface temperatures have been identified as a key driver of strong wind storms in the mediterranean region.

“Climate change leads to higher air temperatures. In turn, warmer air can hold more water vapour. For every 1 °C warming, the air can hold 7% more moisture. In turn, increased water vapour can cause heavier rainfall. Given the long-term warming trend, both in the sea surface temperatures in the mediterranean region and the global air temperature, we expect the events like the currently observed one in Spain to become more frequent.”

Dr Kevin Collins, Senior Lecturer Environment & Systems, Open University, said:

“The speed, intensity and scale of events and the loss of life in the Valencia region and the town of Chiva especially are almost beyond comprehension. Meteorologists are attributing the intensity to the DANA phenomenon where cool air interacts very dynamically with much warmer, moisture-laden air, creating very high storm clouds. Unfortunately, this scenario is increasingly likely as climate change and regional shifts in weather patterns continue. While climate change is not thought to increase the number of storms, it does add to their intensity as every 1oC increase in air temperature approximates to a 7% increase in the moisture holding capacity of the air mass or storm system. In short, warmer air in storms tends to mean more, and more intense rain.

“However, very intense storms do not automatically result in damage. Many other factors are at play. For example, Chiva which experienced severe damage, is located in the upper reaches of the River Turia catchment, close to the mountains. The distance from the mountains to the sea is also very short. This combination means that there is little scope for slowing or absorbing water in agricultural fields or open landscapes, though in this case, it is debatable how much this would have reduced impacts. In other contexts, reduced forest cover from clearances and also climate change, can also mean more water reaches bare and baked ground more quickly adding to the volume and speed of runoff from mountainous areas.

“While warnings were given for SE Spain, the scale and intensity of the rainfall means such warnings offer little scope to avoid the immediate catastrophic damage. To be effective, warnings require people to have ways of managing the immediacy of the crisis, but this event overwhelmed both existing rural and urban infrastructures and also emergency services.

“The storm system is expected to continue for several days as it moves across Spain, leading to more rainfall events. While flash flooding is, by definition, a short-term event, the consequences for people, their livelihoods and regional economies can last for years and even decades as people recover, rebuild, adapt or even abandon areas. In 1957, following major floods, Valencia re-routed the River Turia to reduce flood risk from intense storms. It remains to be seen if this event will require further investment to adapt to a changing climate.

“The impacts in SE Spain will vary. For the specific localities, trauma, shock and a deep sense of loss among the local populations will be widespread and long-lasting. Impacts on agriculture and economic activity will vary but are likely to echo parallel damage in other parts of Spain in recent days from the same weather system. For example, in Almeria, a major food producer for Europe, hailstone damage to greenhouses and crops has been considerable with initial estimates of 30% losses. Apart from the immediate damage, reducing the vulnerability of food systems and supply chains to climate change will drive up food costs, with consequences for all those least able to afford or absorb increases.
“The events in Spain mirror similar recent rainfall and flooding events in Northern Italy and in central Europe. The scale and intensity of these storms show that our societies, technical capacities and our rural and urban infrastructures on which we rely are increasingly at risk in a climate changing world.”

Prof Richard Allan, Professor of Climate Science, University of Reading, said: 

“Weather patterns jettisoned a giant bubble of cold air, a thousand kilometres across, far to the south over the Iberian peninsula and this funnelled huge quantities of moisture up over Spanish mountains leading to sustained and intense rainfall and severe flash flooding. 

“The volumes of rainfall seen were made much larger by human caused climate change that have heated the oceans and increased moisture in the atmosphere by around 7% for every degree Celsius of warming. 

“While it is less clear if climate change is increasing the chances of these dangerous weather patterns occurring, the reduced temperature contrast between warmer and colder latitudes, partly due to amplified warming in the Arctic, is expected to disrupt the jet stream that controls these fluctuations in wind and weather. The resulting extremes of wet and dry, where and when they occur, are being supercharged by a warmer, thirstier atmosphere. 

“Limiting damage and loss of life from extreme weather is only possible through adapting our infrastructure and early warnings to a more dangerous world and crucially by rapidly and massively cutting our greenhouse gas emissions, which is the crux of the problem.”

Dr Linda Speight, Departmental Lecturer School of Geography and the Environment (SoGE), University of Oxford, said:  

“The images and videos from south-eastern Spain show the power of water at its most ferocious. 

“Unfortunately, these are no longer rare events. Climate change is changing the structure of our weather systems creating conditions where intense thunderstorms stall over a region leading to record breaking rainfall – a pattern that we are seeing time and time again. 

“These powerful torrents of water and debris can destroy buildings, wash away roads and sweep people away in seconds. They are impossible to stop. Warnings can be a lifesaver in helping people to seek higher ground and safety before a flood. But as we have seen in Spain today, it is incredibly hard to issue warnings for intense thunderstorms because the exact location of the heaviest rainfall is often not known in advance.  Forecasters and scientists are working hard on innovative solutions to this challenge, it’s not going to be an easy problem to crack. 

“In Spain while the floodwater will go down almost as quickly as it rose, the impacts will last much longer. Damage to infrastructure and blocked roads due to the vast number of cars that have been picked up and moved by the water is making access to the worst affected areas difficult. The risk of collapse of damaged buildings poses a serious threat. Cleaning mud and dirty water out of properties is heart-breaking and the task of searching for missing loved ones even more so. The emotional toll of the floods on those affected has only just begun. 

“We must take the risk of flash flooding much more seriously. This tragedy is another stark reminder of what nature can do when it is angry. We urgently need to adapt our cities to be more resilient to floods. We need to make space for water to flow through our urban environments without causing damage, and ensure individuals, communities and governments are prepared, and resourced, to respond quickly to these types of events when they do occur.” 

Dr Leslie Mabon, Senior Lecturer in Environmental Systems, The Open University:  

“It will take some time for a clear picture of what has happened in Spain to emerge. But factors such as getting warnings out early – and ensuring these alerts get to the most vulnerable people like the elderly who might need more time to evacuate – are crucial for avoiding harm. Having said that, the science is absolutely clear that a warming atmosphere, caused by human-induced climate change, makes extreme weather events like the rainfall that we are seeing in Spain more likely and more intense. These extremes can overwhelm the ability of existing defences and contingency plans to cope, even in a relatively wealthy country like Spain.  

“With COP29, the next UN Climate Change Conference, on the horizon, the floods in Spain are a timely reminder that no country is exempt from the risks of climate change. It is imperative that the most polluting nations take the lead on reducing their emissions, whilst supporting the least well-off in their own countries and globally to adapt to the climate impacts we are already locked into.”

Dr Friederike Otto, Lead of World Weather Attribution at the Centre for Environmental Policy, Imperial College London, said:

“No doubt about it, these explosive downpours were intensified by climate change.

“With every fraction of a degree of fossil fuel warming, the atmosphere can hold more moisture, leading to heavier bursts of rainfall.

“These deadly floods are yet another reminder of how dangerous climate change has already become at just 1.3°C of warming. But last week the UN warned that we are on track to experience up to 3.1°C of warming by the end of the century.

“At COP29 global leaders really need to agree to not only reduce, but stop burning fossil fuels, with an end date. The longer the world delays replacing fossil fuels with renewable energy, the more severe and frequent extreme weather events will become.”


Prof Mark Smith, Professor of Water Science & Health, University of Leeds, said:

“As well as increased rainfall extremes, we are seeing hotter summer which can bake the soil and reduce its ability to absorb water. In turn this amplifies the more direct effects of increased rainfall intensities as more of that water makes it into the rivers.

“Flood warnings in this area have long been challenging. Many streams and rivers are often dry for much of the year and a high proportion of annual rainfall can typically fall within a very short period. When flash floods develop from intense rain, the flood wave can move through the river catchment with tremendous speed. This has been the case for centuries, but with increased rainfall extremes, new areas are moving into zones at risk. While flood warnings in this area are challenging, these events show the importance of renewed efforts here, to improve both the accuracy and communication of these warnings.”


Prof John Marsham, Professor of Atmospheric Science, University of Leeds, said:

What relationship can we say that this type of event has with climate change?
The tragic events in Spain are yet more evidence, as if any were needed, of the rapidly growing destructive impacts of climate change on our societies. The fact that climate change, driven primarily by burning fossil fuels, increases extreme rainfall is one of the most robust aspects of climate science. This gives a rapid increase in flooding with warming. The warmer atmosphere holds more water, and can give more intense storms, allowing heavier extreme rainfall. In addition, there is growing evidence that climate change can lead to slower moving storm systems, leading to greater rainfall accumulations and more flooding.

What role do warnings play in these extreme events?
“Warning systems save lives and have been growing in skill for decades, yet there has still been a tragic loss of life in Spain. We need to prepare for unprecedented extremes and ensure that people are prepared and able to act appropriately.

How long is the flooding expected to continue? What are the impacts likely to be in South Eastern Spain? Are they likely to spread to other regions?
“The media tends to focus on the immediate impact of dramatic floods, loss of life and property, but the impacts will last many years, as people try and recover. Our entire infrastructure and civilization is based around a climate that no longer exists, and increasingly we will see some locations becoming more and more difficult to insure against flood damage, and food and water supplies increasingly hit by increased extreme weather due to climate change.

Any other comments of relevance here.
“As a climate scientist and parent, the ongoing increase in extremes is like watching an avoidable car crash in slow motion. Our global civilization is extremely vulnerable and impacts of climate change will only get worse until we essentially phase out fossil fuels. We know acting quickly will save trillions of pounds, we know people want more action on climate change, and yet the responses of governments are too slow. We have to confront the vested interests from groups such as the fossil fuel industry who in the short term benefit financially from delaying the action we all so urgently need.”

Dr Jess Neumann, Associate Professor of Hydrology, University of Reading, said:  

“The flash floods in Spain are another terrible reminder of the changing and more chaotic weather we are experiencing as a result of climate change.  

“The storms have developed as a result of cooler air passing over the warm Mediterranean ocean, creating atmospheric instability and bringing with it torrential rain. These types of storms can develop quickly and with relatively short warning.  

“Local communities have reported walls of water up to three meters high. The loss of life shows us that we are not fully prepared to deal with storms like those that have hit southeastern Spain.  

“We need to give serious consideration to how we can better design our landscapes, towns and cities. In the longer term, this will need to include radical redesign of urban areas. 

“Flash floods can affect anyone, anywhere. We take preparation for other hazards such as earthquakes and tsunami very seriously with education, drills, and emergency kits. It is time we afforded the same to flood risk preparedness.” 

Prof Liz Stephens, Professor in Climate Risks and Resilience, University of Reading, said:  

“People shouldn’t be dying from these kinds of forecasted weather events in countries where they have the resources to do better. 

“While a red weather warning was issued for the region with sufficient time for people to move out of harm’s way, a red warning alone doesn’t communicate what the impact will be and what people should do. 

“Climate scientists have been warning for years that climate change will lead to more intense rainfall, and the tragic consequences of this event show that we have a long way to go to prepare for this kind of event, and worse, in future.” 

Prof Hannah Cloke, Professor of Hydrology, University of Reading, said: 

“The devastating flash floods in Spain demonstrate how dangerous extreme rainfall can be, even when well predicted. Despite AEMET issuing a red weather alert, we must do better in communicating the dangers of extreme weather so that lives are not lost unnecessarily.” 

The comments below was provided by our friends at the Spanish SMC:

María José Sanz, Scientific Director of the BC3 Basque Centre for Climate Change, said:

“Attributions are always tricky. Generally speaking, the jet stream, because of the changes we are seeing, due to climate change, is having more pronounced undulations. DANAS are areas of low pressure that are isolated from the jet stream. Although they are frequent, they happen more in winter, when these undulations occur.

“In addition, as we have more water in the atmosphere right now because the oceans are warmer due to the increase in temperatures, this factor is added to the previous one and causes intense phenomena.

“We will have to see what conditions have occurred, where this isolation of low pressures has taken place or the amount of evaporation, among other issues.

“There are also atmospheric rivers, certain currents in the atmosphere that transport water vapour. There are studies that indicate that extreme phenomena in California were related to this factor.”

Dr Ernesto Rodríguez Camino, Senior State Meteorologist and member of Spanish Meteorological Association, said:

What relationship can we say that this type of event has with climate change?

“In general terms, what we know is that, in the context of climate change, these types of intense and exceptional, rare rainfall events are going to become more frequent and more intense and, therefore, destructive.

“That is in general terms. Events of this type, which used to occur many decades apart, are now becoming more frequent and their destructive capacity is greater.

“Associating a particular event like this to climate change, i.e. asking the question that if we had not had climate change we would have suffered an event like this, requires a posteriori studies and can always be said in probabilistic terms, but not on the fly. This is something that will be analysed and these very destructive or very violent cases, then give rise to many studies that are done in academic and research fields.

“We can’t say anything on the fly, except that in the context of climate change, these types of events will be more frequent and more intense.”

What role do warnings play in these extreme events?

“What we have to bear in mind is that warnings are issued for relatively large areas, at the county level, and then the most extreme consequences are at the point level, often at the municipality level, and this depends on many other things that have nothing to do with precipitation.

“The warnings issued by the State Meteorological Agency, AEMET, refer to precipitation, which is AEMET’s responsibility. But whether that rainfall then has more or less destructive effects also depends on the orography (geography dealing with the formation and features of mountains), on rainfall upstream, on public works, on where the municipalities are located, on whether there are obstacles or not…. All of this is something very particular. Between heavy rainfall and its destructive power, there is a whole chain of actions that must also be considered.”

Declared interests

María José Sanz: No conflicts of interest.

Prof John Marsham: No conflicting interests, and has research funded by UKRI and FCDO.

Dr Friederike Otto: No interests to declare.

Dr Leslie Mabon: “is an Ambassador for the National Centre for Resilience in Scotland, a cross-sector partnership spanning Scottish universities, government and practice committed to improving country-wide resilience to natural hazards. This is a voluntary position for which he receives no renumeration. Whilst Dr Mabon shares the NCR’s ethos of supporting an evidence-driven response to reducing risks from natural hazards, he is commenting in a purely personal capacity.”

Prof Richard Allan: no interests to declare.

Dr Kevin Collins: no interests to declare.

Prof Hannah Cloke: “works with and advises the Met Office, ECMWF and Environment Agency.”

No reply to our request for DOIs was received.