The second DANA, which devastated Spain in less than two weeks, revealed the fragility of regions as far away as Malaga and Tarragona, the epicenters of this second assault. They are part of a map that covers 25,000 square kilometers and affects nearly 3 million people: the map of Spain at risk of flooding.
The Spanish Meteorological Agency (AEMET) issued a red alert on Tuesday evening in these two provinces, with precipitation potentially exceeding 200 liters per square meter in 12 hours. Valencia joined them this Wednesday afternoon, with cumulative quantities of up to 180 liters per square meter.
The capital of Malaga and its inland areas suffered flooding. Previously, classes had been suspended in part of the province, as well as the high-speed train that connects it to Madrid and the C2 line of the Cercanías service.
In Tarragona, classes were also suspended and the AP-7 collapsed due to mobility restrictions. Several Rodalies and Renfe lines were paralyzed. For its part, in Valencia, which was a black spot in the previous DANA, train services were reduced and the movement of private vehicles was restricted.
Floods are a frequent phenomenon in our country and will become even more so due to the effects of climate change. The data that evaluates its risk does so by evaluating a frequency of 10, 50, 100 and 500 years.
According to the Ministry of Ecological Transition and Demographic Challenge (MITECO), 2.7 million people live in areas likely to be flooded every half a millennium. If the time estimate is reduced, There are nearly 500,000 citizens living in areas that may experience this situation every decade.
These figures only cover intercommunity basins, which are those that depend on the organization. If we add the others, it is estimated that this number could reach around 700,000 inhabitants. The intercommunity basins with the most floodable kilometers are those of the Ebro (more than 3,500 kilometers), Júcar (more than 3,400), Duero (more than 3,200), Guadiana (1,800), Segura (1,800), Tajo (more than 1,600), Western Cantabria (1,200) and the Guadalquivir (approximately 1,200 kilometers).
Areas most at risk of flooding in Valencia.
The company DOTGIS, dedicated to geospatial analysis, published a report in 2021 in which it calculates the most populated Spanish municipalities at risk of flooding. Four of them were in the Valencian Community: Massalfassar (55.1%), Quartell (54.5%), Benavites (51.5%) and Alfara del Patriarca (49.1%).
Next come two municipalities in Tarragona: Deltebre and Sant Jaume d’Enveja, with respectively 86.3% and 64.8% of the population at risk.
Salamanca has Castraz and La Maya, which have 69% and 67% of their residents in vulnerable areas. Calatayud (Zaragoza) also appears in this decalogue with 57.7% and Betanzos (A Coruña) with 51.8%.
Malaga, although it does not appear in this famous top 10, also has a tradition of flooding, largely associated with the bed of the Guadalmedina river. Although more than 30 years have passed since the last floods, the river’s flooding over the past centuries has caused casualties numbering in the hundreds.
Houses in flood zones
In this issueor we may lose sight of the effect of population expansion toward the margins of river channels and boulevards. “We build more and more and if it is done in one way or another, anywhere, we end up being more vulnerable,” says Nieves Sánchez, president of the Official College of Geologists. The scientist also spoke about the investments required by these events. “The company is losing a lot of money by not doing things right.”
Andrés Díez, flood expert at the Geological and Mining Institute of Spain (IGME), explains that the urbanization of these enclaves influences the orography and infiltration capacity. To build in these riverbed environments, the land is usually leveled. This means that buildings are located at lower levels relative to the river and are more easily flooded. To illustrate this, the expert gives the example of Letur (Albacete), where DANA caused six deaths on October 29.
Areas most at risk of flooding in Malaga.
The other aspect to evaluate is the reduction in soil infiltration. This urbanization is generally accompanied by the paving of the surface. In this way, the soil loses its ability to absorb water and, when it rains, “everything that falls goes straight into the river,” explains Díez.
When these phenomena occur, the liquid flow of rivers does not enter the channel and uses these flat areas to overflow, explains geologist David Uribelarrea, professor of geology at the Complutense University of Madrid (UCM). If the area is occupied, water can wash away everything in its path.
Uribelarrea, also an expert in river environments, also talks about the increase in urbanization over the last 60 years. ANDIn the 1956 aerial photograph, practically no buildings in Spain can be seen in these flood zones.. “People knew they were only useful for agriculture and not in their entirety.”
Díez agrees with his counterpart and points out that with this expansion of urbanization there is also the paradox that the most vulnerable buildings (due to their personal value) are those that are at greatest risk. “Whereas before you had a hayloft that, if it flooded, nothing would happen, now you have a retirement home.” When constructing permanent buildings, in addition to increased flooding due to orographic change, the risk also increases.
More urban planning, more water speed
Sánchez warns that any work will affect the land and the way water flows in extreme cases like this. “This diverts the course and generates a change in the situation,” he emphasizes. Naturally, once the canal overflows, it follows natural drainage routes, indicates the UCM professor. Typically it leaves large areas of shallow waterlogging.
However, if this water must pass through an urbanized area, andFlow space can be reduced by 80% or more. “The result is that the draft increases and, above all, the speed at which it takes place,” explains Uribelarrea. The geologist adds that in addition, in situations like last Tuesday, the water is not clean. The magnitude of the storm causes soil loss, carries more sediment, and has more force.
The president of the Official College of Geologists explains that, to know this type of information, there is geological mapping. Sánchez also points out that projects should also be examined by those experts who could assess the risk of urban projects. MITECO has maps in which flood zones can be viewed in periods of 10, 50, 100 and 500 years in Spain, which, according to the IGME expert, must be taken into account before planning the works.
If the floodplain is already occupied, risk maps are the best allies, believes Uribelarrea. They are used to better plan the most dangerous areas, evacuation and access routes, as well as alarms for the population, he explains.
The UCM professor is clear and affirms that once the land is urbanized, it is very complicated. What will work best is a good alarm system and evacuation protocol. However, he regrets that in Spain “there is no culture in this sense”.
