Less rains, but torrential: Spanish cities shield themselves against the flood alert

• GUILLERMO DEL PALACIO

• JUAN C. SÁNCHEZ

  @_JuanCsanchez_

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Updated on Monday, 15November2021-22: 01

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In recent years, the way it rains in the Iberian Peninsula has changed and now rainfall is less frequent, but the water falls

. This causes drought problems, but also others that directly affect urban planning and even architecture. Spain, experts warn, is not prepared for these new storms and floods could be more frequent, but there are solutions and some are already being applied.

Naturally, the rains are quite irregular in Spain, which makes it difficult to study.

However, the AEMET is noticing "a trend", according to

, meteorologist and spokesperson for the organization: the dry periods are getting longer (especially in the south of the peninsula), but the days in which it rains, it does so in large quantities.

"That torrential rain is even more intense, especially in the last decade."

Although there are indications that the 'new rains' affect the Cantabrian and Atlantic slopes, it is especially noticeable in the Mediterranean region, where historically there are already flood episodes with cold drops, and it has also been detected that there is "a greater frequency of episodes ".

Del Campo for the moment prefers not to blame climate change directly for this new trend - it is

- because of how difficult it is to study such irregular phenomena as rainfall.

"All predictions suggest that in an environment of warmer seas and more energy available in the atmosphere, extreme precipitation phenomena can increase," says the meteorologist.

"We are at the starting point," says del Campo, so we must continue to analyze the trend, "but, above all, we have to start taking it into account."

"In recent decades we have underestimated that risk, which already existed," warns the expert and "we have occupied floodplain areas."

"The problem is going to increase", sentence.

Urbanism and awareness

"You cannot tear down the houses; you have to carry out works of another type", sums up

, professor of Regional Geographic Analysis at the University of Alicante, who confirms that there is part of the territory "unduly occupied".

"What do we do with those homes or urbanizations that have occupied areas at risk of flooding?" Asks the professor, who also answers: we must go to engineering, but also to raising awareness.

That is, that people living in risk areas know the danger and know how to act when they receive alerts.

In any case, Olcina believes that "little by little" the risk is being known and measures are already being taken. "

: when an episode occurs and there is a lot of damage or a victim is when we worry and the Administration tries to do something," he concedes. In fact, since 2008 the land law requires having risk maps, although the expert considers that these have "many shortcomings" and it would help the Administration to publish a guide with the minimum contents that these documents should contain. "On those maps we play a lot," he warns.

The expert also points to the opportunity - and need - to use European funds to adapt cities to the new torrential rains: "We do not have the sewage systems prepared to take on the intense rains that have been registered lately in our country."

"They were designed for other climatic conditions, decades ago and now the situation has changed", explains Olcina.

A funnel

In a way, a city's drainage system is like a funnel that collects falling water and transfers it to prevent flooding.

But also a funnel can overflow if more liquid enters than comes out.

When this happens, the system collapses and the water becomes runoff that floods the streets.

"When we see flooded cities, the water runs upwards like a river, but it is also running through the urban drainage pipes at full speed," says

, president of the Spanish Association of Water Supply and Sanitation

. The easiest way to avoid that the pipes are so stressed is, logically, to change them for larger ones, but this, if it can be done, supposes an enormous expense that becomes a waste if the torrential rain is a punctual phenomenon .

Morcillo explains that, although the change in rainfall is "a challenge" that the sector has already detected, undertaking a total reform of the drainage system is something for which they would need more. "For urban drainage purposes, we must think that sewerage techniques are in principle conceived to ensure that a neighborhood or city is not flooded with a recurrence period of certain years," he details.

That is, they are created to withstand the levels of rainfall that occur in a certain area according to the historical archive.

A flood every, for example, 25 years is a statistical anomaly that cannot be contemplated in the sewer system;

one every year means that the system fails for some reason, such as the way it rains has changed.

But that does not mean that there are no solutions, such as

.

Parks and tanks

Both the tanks and the parks are based on the same idea: 'separate' the water so that the system does not collapse.

They thus become temporary reservoirs to which to direct the rains that the urban drainage cannot assume.

The difference is that some do it in the subsoil and the others, on the surface.

"Let's imagine a big garage", Morcillo compares, "what happens is that instead of having plants for the cars to be in, there is a huge tank under the plot".

Canal de Isabel II boasts that Madrid has "the two largest storm tanks in the world" -the

, with the capacity to store up to 400,000 cubic meters of water each.

In other words, the equivalent of emptying eight ponds like El Retiro.

According to the AEAS director, this solution makes more sense "in the center of large cities", as long as parking and urban transport allow it.

"It is not so easy to do it always because cities are as they are and are made as they are made," he argues.

Floodplains, for their part, make their role quite clear in their name. "It means making enclosures that can be flooded", summarizes Morcillo. Since the normal thing is that they do not have to be used, in the day to day they can be used as a green element of the city, with its lawn and gardening, but in the shape of a trough to give a break to the sewers in case of extreme rainfall. When the clouds go away - or, at least, they stop discharging - the water is redirected to a treatment plant.

"You have to adapt," sums up the manager.

The climate changes and the role of urban planning is to identify this change and take "small actions" to reduce the impact.

Sometimes, he exposes, it will only be necessary to operate in a certain area where a bottleneck occurs.

In this sense, it takes the opportunity to load

, which should never be poured down the toilet: "It is a material that if it does not disaggregate in the water tends to cause clogs or clogging incidents in the tubes."

Sustainable drainage

A third way, not necessarily exclusive, involves making the city itself help drainage.

It is what is known as

, Sustainable Urban Drainage Systems.

Soils are made more permeable and water infiltrates the subsoil in a more natural way, as if civilization were not there.

"The cities are an artificiality", argues Morcillo.

Almost all the ground is paved and very little permeable - tree grills, green areas and some flower beds are the only exceptions - so the rain ends up forced to travel the same path as vehicles and pedestrians until it leads to a drain.

The SUDS are a middle ground.

Thus, for example, in surface car parks you can choose a material other than asphalt;

a pavement sufficiently bearing so as not to get muddy, but which at the same time has porosity to filter.

There are also rain gardens, vegetated roofs, infiltration ditches or cisterns, among others.

All of them allow, to a greater or lesser extent, to reduce runoff while still fulfilling a function.

To new rains, new cities.

According to the criteria of The Trust Project

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