Spain 2024 floods: how the DANA, soil, sea and Jet Stream interact.

Climate change has intensified the DANA weather phenomenon, unleashing severe storms across eastern and southern Spain. In parts of the Valencia region, rainfall exceeded annual totals within a single day, reaching 400-500 mm. Observers, particularly earth scientists, will have noticed the water's opaque reddish brown hue as it surged through the streets in a haunting, chocolate-colored torrent—clear evidence of extreme soil erosion upstream. This erosion is a direct outcome of centuries of exploiting natural resources, initially only affecting the environment but now revealing the deeper consequence of eroding the very foundations of our civilization. In this post I share some reflections on soil and the atmospheric forces that have transformed this DANA event into a humanitarian crisis.

Author: Kathelijne Bonne.

What is a DANA? This much talked about Spanish weather phenomenon translates as a "depresión aislada en niveles altos," or a "cut-off low" in the higher atmosphere, detached from the Jet Stream. These pockets of cold air occur mainly in the fall. It causes intense downpours, thunderstorms and cold weather. Due to climate change, DANAs occur more frequently and have become more severe. The term gota fría (cold drop), taken literally from German Kaltlufttropfen, is used as well even though in Spain it has become an umbrella term to refer to any intense rainfall event.

The collision of a cold cut-off low (DANA) with the still warm and intensely humid air over the Mediterranean Sea, causes torrential rains, which are even more intense in a mountainous country like Spain: air that is forced to rise will cool, and the vapor will condense.

Soil erosion

When torrential rains hit barren farmland, the upper layers of the soil are washed away. Sheet, rill and gully erosion then cause massive damage. The topsoil (which is always the most fertile) ends up in reservoirs, on river banks and in the sea.

And in the recent severe weather event of late October 2024, it ended up as mud in streets, towns and houses. The stream of volunteers who set out on foot to the hardest-hit areas, armed with brushes, buckets and mops, will fight a battle against mud and 'dirt'. But in fact, this dirt is 'good earth,' an essential element that can no longer contribute to ecological restoration or food production.

Spain, rich in a multitude of soil types, has faced severe soil erosion for decades, losing an average of 1.4 million tons of soil per day, a result of centuries of deforestation and predatory agriculture. Systematic tree felling started with the Romans and continued with the expansion of the Spanish Empire when wood was needed for shipbuilding. In later times, population growth and the rise of industrial agriculture caused more land clearage.

Spain's relief is mountainous and its climate semi-arid, making it particularly susceptible to soil erosion. The washing away of huge volumes of earth has even created new landforms entirely due to anthropogenic erosion: new river terraces and deltas.

The result is an interior landscape left barren and void of greenery for much of the year, leaving the soil exposed and vulnerable to the relentless effects of rain, sun, and wind. As the soil has lost its internal coherence, it has become vulnerable to wind erosion as well. Another post on Spain mentioned the Dust Bowl disaster in North America, also a result of deforestation, over-tilling, and complete land stripping. In Spain, olive and almond groves, among others, are particularly worrying. The land on which the trees stand is completely bare, with no not one leave of grass to protect it from the impact of precipitation or drought.

Protecting built-up coasts

Soil degradation is bad enough in itself because it impacts food production. And instead of an ally, the barren interior becomes an enemy as a source of dirt that can be washed to downstream populated areas, infrastructure and cropland.

To fully appreciate all the risks, the situation must be viewed from a river catchment perspective. The entire Spanish coastline is build-up and located downstream of a high hinterland. To protect the urbanized areas along coasts, climate-robust infrastructure or a more efficient warning system will help, but they are only a patch if soils and natural vegetation in the catchments are not restored. We won't be able to fight nature forever, we must embrace her as our ally.

Reforestation and making agriculture more sustainable are crucial. Natural vegetation acts like a sponge, breaking the impact and eroding power of precipitation and runoff. And when soil regenerates, organic material and biodiversity increase, making the soil spongier, which promotes infiltration and water retention.

Allowing strips of nature (woods, shrubs, grasses) to grow between croplands, water is retained and water and the plants serve as windbreaks. Main crops should alternate with a cover crop, such as clover, vetch, rye, oats or alfalfa, so that the land never lies fallow. Natural wetlands such as Doñana and La Albufera (Valencia) should be restored, giving them back their buffering capacity. The natural course and floodplains of rivers should be considered when planning infrastructure and habitation. The resilience planning must include the entire river basins running up to watershed divides in the mountains.

Improving human and infrastructural resilience alone, is like putting a band-aid on a bullet wound.

Cars and concrete

Will policymakers learn anything from this DANA? Nature and climate have consistently ranked low on the political agenda, particularly until the year 2000, and environmental organizations are often perceived as nuisances that hinder economic growth. In my municipality of Torrelodones, near Madrid, environmental awareness appears almost nonexistent—were it not for the presence of dedicated activists. Untouchable developers are transforming once-wild landscapes into unrecognizable concrete wastelands, with paving and asphalting on the rise. The 'best' policy decisions prioritize the convenience of motorists by creating more parking spaces and constructing new slip roads where green spaces once thrived.

These developments in Torrelodones exemplify a broader trend throughout Spain. Along the coasts, the situation is no different. Massive urban sprawl is evident, particularly on the Costa Blanca and elsewhere.

Pondering on cars and concrete, has the reign of motorists finally met its outer limits? This thought crossed my mind when I saw images of countless damaged cars in Valencia, jumbled together in flooded streets—some likely still having people inside. The number of images depicting broken cars far exceeds those of people. The extent of the car damage must be astronomical, which, absurdly, will benefit car manufacturers.

With my views on cars, I seem to drift off-topic. Or is this the crux of the matter? It is for driving that so much concrete and asphalt is produced, that surfaces are paved over, preventing rainwater and floodwaters from being absorbed by the soil, thus hindering its ability to provide essential ecosystem services. Furthermore, isn't it the emissions from driving, transportation, and other sources that contribute to climate change, exacerbating natural disasters?

Jet Stream and DANA

Now that we're back to climate, let's look at where the DANA phenomenon comes from. It originates in the Jet Stream, the atmospheric conveyor belt that travels through the troposphere at high levels. The Jet Stream separates cold polar air in the north from warm air in the south. It flows from west to east across the planet like a meandering river. The weather in Europe is largely determined by the Jet Stream, but also by the behavior of the atmosphere over the Atlantic Ocean. Above the Azores and above Iceland are two large "fixed" atmospheric pressure systems: the "Azores High" around which air rotates clockwise, and the "Icelandic Low" around which air rotates counterclockwise. Together this system is known as the North Atlantic Oscillation. The Jet Stream meanders between these large 'driving wheels,' driving depressions and disturbances towards Europe.

The Jet Stream sometimes has to deflect when something blocks its path, as was the case in late October of this year (2024). A very stable high-pressure area, called a "blocking high" lay stationary over Central Europe, leading to clear October weather. The Jet Stream could not get past it and took a detour along the north of the block.

But a piece of the jet stream was cut off at altitude: a DANA or cut-off low. It gets isolated from the general stream and bends to the south. It heads towards the Iberian Peninsula. It collides with warm Mediterranean air, which has been much warmer than normal. Hence, evaporation of seawater is higher too, and so is the overall humidity. 

The floodgates of heaven open.

We know what it can lead to.

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In this article, I closed my eyes to the suffering of the affected population, as words fail. Moreover, the human aspect is already widely covered in the media. I am also trying to see this in a larger context. The suffering here is no different from that in other climate disasters worldwide. Floods combined with soil erosion strike on a much larger scale and with greater regularity in other (especially poorer) countries. Then I think of Pakistan (2022), Nigeria (2022), Bangladesh (amplified monsoon, 2022, 2023), Chile (2023), India (2023). But Italy (2023), Greece (2023), Canada (2023) and the United States (2024) did not escape climate disasters either.

My thoughts wander back to Valencia. There are only two inhabitants I know by name, two white beluga whales in the Oceanografic, Yulka and Kylu. Are they safe in their tank that is actually right in the middle of the old bed of the Turia River? Doesn't the whole thing prompt reflection? Don't they belong in the sea? They should be returned to the sea, so on land, we can try to solve land-issues.

Kathelijne: I am intrigued by how earth, life, air, ocean and societies interact on geological and human timescales.

Why I started GondwanaTalks.

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