The scientific community (at least most of it) recognizes the existence of climate change. And not only that. A non-negligible part of its members believes that the phenomenon is moving with such inertia that it will be difficult to do anything to reverse it, in any case minimize it. In this group is Corrado Altomare (Terlizzi –Italy-, 1981). This civil engineer, and Ramón y Cajal researcher at the UPC School of Civil Engineering, aims to develop a model that helps predict how urban coastal defenses will respond to extreme wave conditions under various future climate scenarios. And the BBVA Foundation has just awarded him one of the Leonardo scholarships (which are in their 10th year) to make it a reality.
What is the project about?
It consists of characterizing the flows of waves of water masses over structures that we technically call overflows, that is, the flow of water that passes over a coastal structure, such as a boardwalk, and that can cause damage to people, properties and floods. We are clearly facing climate change. We have already experienced meteorological phenomena such as Gloria, in January 2020, a type of storm that will increasingly become more frequent and intense. And here we are no longer talking about a question of resistance of the coastal system, but rather of resilience. Maybe you resist the first storm, also the second, and the third. But what about the fourth? During the previous ones, it should be taken into account that the beach has been eroded and the damage has been accumulating.
Can you quantify what overshoots climate change will bring?
It is the first thing we want to calculate in order to determine what awaits us: what water flows we are talking about, volumes, speeds and damage that we may have if we do not intervene. For example, if a person has his feet in a flow of water caused by overtopping waves, he can hold on or be swept away. What does it depend on? Not only the speed of it, but also the amount or height of this water flow. It is a combination of both. Currently, there is no clear methodology established to calculate the effects of overtopping on structures such as boardwalks, which are increasingly affected by sea level rise, and this is what we want to assess and do.
In Spain, what are the most vulnerable areas?
The Basque Country, for example. The entire Cantabrian area faces very intense waves, much greater than in the Mediterranean and with greater frequency. However, the Mediterranean area is also sensitive: you only have to look at the damage caused by Gloria, which left maximum waves of 7 meters, or even a little more depending on the location. In the Cantabrian Sea, however, they can reach 14 meters.
The double?
Yes, and it is a longer wave, with a longer period. The longer a wave is, the faster it is and the more likely it is to overtake. I explain to my students that a longer wave is similar to a tsunami, if we take it to the extreme. He is less affected by what happens below. It is so big that, even if it finds something in the depths, it easily goes up the beach. A tsunami is the most extreme example: it destroys everything because it is a wave the size of kilometers and has a lot of thrust.
The methodology they intend to create would be a good prevention tool.
Of course. If we have a forecast of the possible rise in sea level and wave height that a specific storm could cause, we could determine, once we have the methodology ready, the overtopping that could occur and its effects. With this information, the competent authority can make decisions to protect its promenades and citizens. For example, putting more sand on the beach, because it dissipates more wave energy, or modifying the geometry of the walk.
Is there any population that has taken measures of this type?
I was working for many years in Belgium. There, the situation is more sensitive because the country is below sea level. In one of its towns (Wenduine), some modifications were made to protect the seafront. However, if you go to town and walk along the seafront it does not appear that any action has been taken. Because? Because the modification consists of two benches where people sit and do not know that they have a function, also during storms. There are two benches with a backrest each of around 80 cm and separated by about 11 meters. What they do is slightly increase the protection height of the promenade and causes the waves, in the context of a major storm, to impact on them, dissipating the energy. All of this reduces the impact.
I understand that sea level rise greatly influences the overtopping phenomenon.
It's exponential. A small rise means much more flow. If you can define the amount of overflow you have, prevention policies can be established based on that data. If I know that a specific storm is coming in the next few days that will cause a known overtopping, I will be able to determine whether or not to close public access in a specific area since a dangerous amount of water is expected there.
Structures such as boardwalks, are they in danger?
It depends a lot on the area, but they can be. Above all, in cases where there is a lot of beach erosion and perhaps it does not regenerate afterwards. The fact that there is no beach translates into more interaction of the waves with the structures of the promenade and with larger waves. And this can be more critical when you have a vertical structure, because it can also generate greater erosion at the base, which can end up collapsing.
It is essential, then, to regenerate the beaches.
In general, a very wide or very long beach dissipates more energy, because the waves break. The more energy is dissipated, the less overtaking you have, that's clear. But there is also a limit to beach regeneration. There may be areas where it is not possible, because it is expensive, or there is no sand nearby to use. In these situations you have to think about other solutions.
There are underwater structures that can also help minimize the impact of waves.
Yes. For example, a breakwater slope, of a determined and studied size, that is not visible from the beach, because it is submerged. The wave, upon arrival, interacts with this barrier, undergoes a process of surfacing (rises) and breaks, which dissipates its energy and protects the beach.
When is sea level rise expected to become very problematic?
By 2100, the IPCC predicts a maximum rise of 0.84 meters if greenhouse gas emissions continue to increase throughout the 21st century. We work with this time horizon. As I say, this forecast is subject to what our governments decide to do or not. A rise of 0.84 meters is outrageous, because it changes the entire sediment transport of the coast, floods areas and can also generate a lot of overtopping. All this means facing very important problems.
Are you optimistic about stopping climate change?
I am very skeptical. I think we have already entered a climate change trend and we have not acted in time. And the context doesn't help either, with the wars that exist in different parts of the planet. We are investing in other things. The trend of climate change is very difficult to reverse. Therefore, we have to invest in protecting ourselves, and also in damaging less, investing in renewable energy. We can combine both, but we have to protect ourselves and adapt.
And get away from the coast?
A possible alternative, although we will never carry it out, is to move the city. I mean, let's let the sea do what it has to do. If you have to erode the beach because it is not natural, let it erode it. It's a controversial approach, I know. We have modified the system and we have the duty to maintain it and protect the population. But, in theory, there is also that option, although it has great economic impact: there are infrastructures, businesses, tourism...
Many people live on the coast.
In Europe, 41% of the population lives there. It's something very serious.
I don't know if the trend, now, is to leave the coast due to the possible effects of climate change.
According to recent studies, the trend is the opposite: more and more people are going to live on the coast, in the big cities. So, if there is a forecast of increased population on the coast and, at the same time, a forecast of increased risk from climate change, we will have to look even more at the effects on coastal structures.
But isn't this tendency to continue heading towards the coast nonsense?
The coast offers resources, business... it has always been like this and always will be.
