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

Climate change has intensified the DANA weather phenomenon, unleashing torrential rains 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 rusty 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 consequences 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.

Text and photographs: Kathelijne Bonne.

What is a DANA? This much talked about Spanish weather phenomenon translates as 'isolated depression in high levels' (Spanish: depresión aislada en niveles altos),  known as a "cut-off low". These pockets of cold air originate high in the atmosphere and are detached from the Polar Jet Stream. Cut-off lows hit Spain mainly in autumn. It causes intense downpours, thunderstorms and cold weather. Due to climate change, DANAs occur more frequently and are 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 (the DANA) with the still warm and 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. Furthermore, the Mediterranean is much warmer than usual, increasing evaporation and humidity, hence adding gunpowder to DANA phenomena. 

Soil erosion

When torrential rains hit barren farmland, the upper layers of the soil are washed away. Sheet, rill and gully erosion and flash floods 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, undergournd parkings and houses. The 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, with its multitude of soils, has undergone 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 contributed to further clearing.

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 barely a few leaves of grass to protect it from the impact of precipitation or drought.

Protecting built-up coasts

Soil degradation is worrying enough in itself because it impacts food production. And instead of an ally, the barren interior becomes an enemy: it has become 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 natural vegetation in the catchments must be restored too. 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 the bushes 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. Any resilience planning must consider the entire river basins running all the way up to the 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 havens into unrecognizable concrete wastelands, with paving and asphalting on the rise. The 'best' local achievements reflect the convenience of motorists by creating more parking space and constructing new slip roads where green spaces once thrived.

Torrelodones is just one case of a larger trend happening across Spain. Along the coasts, the situation is no different. Massive urban sprawl is evident, particularly on the Costa Blanca and elsewhere.

And as I ponder on the devastation in Valencia shown in media, I couldn't help noticing countless damaged cars, jumbled together into flooded streets. Some cars may still have people in them. Underground parking lots have become a grave for some of the victims. 

But the car scenes hide another, larger unconvenient truth: The overwhelming excess of cars we've come to accept as normal, and even as symbols of prosperity, may ultimately lead to the undoing of the latter. 

My impressions regarding cars may seem off-topic, but they actually address the crux of the matter. It is for cars that so much concrete, asphalt and paving are produced, creating deadly traps, preventing rain and flood water from seeping into the ground and preventing the soil from performing its essential ecosystem services.

We would almost forget, but emissions from cars, amongst others, ultimately warm the climate, intensifying natural disasters. 

Jet Stream and DANA

Now that we're back to climate, let's look at the origins of the DANA phenomenon. It originates in the polar 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 there are other factors too, like 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: 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 and produces more moisture than normal. The moisture condenses. 

The floodgates of heaven open.

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In this article, I closed my eyes to the suffering of the affected population, as words fail. But as the human aspect is already widely covered in the media I try to see things in a larger context. The suffering here is no different from that in other climate disasters worldwide. Floods combined with soil erosion have struck on a much larger scale and with greater frequency 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 turmoil either.

My thoughts wander back to Valencia. There are only two inhabitants I know by name, Yulka and Kylu, two white beluga whales in the Oceanografic. 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 our land-issues.

Soil salinization is another form of soil degradation, also affecting Spain. Or read on the role of nitrogen, on black soils in Ukraine and how they endure war, or on drought in national park Doñana. The Mediterranean has already evaporated in the past, find out what the repercussions were. Or, if you prefer something more uplifting, read my recent post on how life thrived and evolved in times of the great continent Gondwana.

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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