The October 2024 floods in Valencia were driven by an isolated high-altitude depression which caused catastrophic damage and loss of life across the region. Triggered by an unusual concentration of rain, up to 500mm in just eight hours in some areas, this intense weather system overwhelmed Valencia’s infrastructure which left vast urban and agricultural lands submerged.
Spain’s meteorological agency (AEMET) noted that this pattern reflects a broader shift toward shorter, intense rain events which increase flood risks despite similar annual rainfall totals. As inland rivers and streams overflowed in the Valencia Region (Comunidad Valenciana), coastal drainage was further obstructed by a strong maritime storm which compounded the disaster’s impact.
Please note that the photographs in this article are not from the Valencia region. They are my own photos from a similar meteorological event in the Granada region some years ago.
What Caused the Floods in Valencia?
The floods in Valencia were the result of a meteorological phenomenon known in Spanish as a DANA (Depresión Aislada en Niveles Altos). Known in English as a ‘cut-off low’, it refers to an isolated area of low pressure which becomes separated (or “cut off”) from the main flow of the westerly winds in the upper atmosphere.
DANAs are particularly significant in Spanish weather because they can cause:
- Intense and persistent rainfall
- Sudden temperature drops
- Severe storms
- Flash flooding
These systems are most common in spring and autumn around the Iberian Peninsula. Unlike typical low-pressure systems, DANAs are isolated from the general atmospheric circulation, which makes them relatively stationary and can lead to prolonged periods of severe weather in one area.
The term is particularly used by AEMET (Agencia Estatal de Meteorología), Spain’s state meteorological agency, which also refers to them as a “gota fría” (cold drop), although technically these are slightly different phenomena.
Do DANAs only occur in Spain?
No, DANAs occur in many parts of the world – they’re just particularly well-known in Spain due to their significant impact on the Mediterranean coast and the specific term being popularized by Spanish meteorologists.
The same phenomenon is known by different names in other regions:
- In English-speaking countries: “Cut-off low”
- In Germany: “Kaltlufttropfen” (cold air drop)
- In France: “Goutte froide” (cold drop)
These systems can form anywhere where upper-level low pressure systems can become isolated from the main polar or subtropical jet stream. They’re common in:
- The Mediterranean Basin
- The Australian region
- The eastern Pacific off California
- South America, particularly near Chile
- Southern Africa
The reason they’re particularly notorious in Spain is because when they occur over the Mediterranean, they can draw in warm, moist air from the sea and force it up against the coastal mountain ranges, leading to extremely intense rainfall events. This combination of geography and meteorology makes them especially impactful in the Spanish context, but the basic atmospheric mechanism occurs globally.
Danger of Coastal Flooding
The relationship between DANAs and coastal flooding in Spain represents a complex interplay of geography and meteorology. The Spanish Mediterranean coast is characterized by steep mountain ranges running parallel to the shoreline, with numerous “ramblas” – typically dry river beds – forming natural channels from the mountains to the sea. Many coastal cities and towns have been built in historically flood-prone areas, including over these ancient ramblas, creating inherent vulnerability.
When a DANA occurs, the heaviest rainfall often falls in the interior mountain areas. The land, frequently parched and hardened by Spain’s hot climate, cannot readily absorb this sudden influx of water. Instead, the rainfall rapidly channels through the rambla system, gathering speed and volume as it races downhill toward coastal settlements. This means coastal areas can experience severe flooding even if they receive little or no local rainfall during the DANA event.
Modern urban development has exacerbated these natural risks. Many ramblas have been built over or narrowed, whilst natural drainage areas have been covered by concrete and asphalt. When flood waters arrive, urban storm drain systems can quickly become overwhelmed. The speed at which this inland water reaches the coast often leaves little time for warning or preparation in coastal areas.
The flooding presents particular dangers in urban environments. Underground structures like parking lots and basements are especially vulnerable to rapid inundation. Roads can become impassable within minutes, and the floodwater often carries debris that increases its destructive potential. This is why Spanish meteorological services strongly emphasize avoiding ramblas and dry river beds during DANA events, even when they appear safe, as deadly flood waters can arrive suddenly from rainfall that occurred many kilometres inland.
DANA Weather Warnings
Whilst DANAs can be predicted, their exact intensity and precise location can sometimes be challenging to forecast with complete accuracy, as these systems can be somewhat erratic in their development and movement. Local authorities often advise citizens to stay updated with the latest forecasts as conditions can change rapidly. Civil Protection authorities also activate emergency protocols based on these warnings, which can include school closures, event cancellations and evacuation recommendations in high-risk areas.