"Sea level rise is one of the factors that most increases the danger of storms"

15/05/2025

AZTI researcher, Aritz Abalia has developed an early warning system to predict the impact of storms on the Basque coast. His PhD thesis, defended at the University of Pau et des Pays de l'Adour, was supported by the LIFE IP Urban Klima 2050 project.

The Basque coast, highly urbanised and diverse in terms of beach typology and protection structures, presents an important challenge when it comes to assessing the risk of coastal flooding. This has been the object of study of the PhD thesis by Aritz Abalia, researcher at AZTI, focused on the assessment of the threat of coastal flooding at different spatial scales on the Basque coast.

"It is not possible to apply a single tool to analyse the entire coast, because each area is different: there are open beaches, sheltered beaches, harbours, protective structures, etc.," explains Abalia. Given the difficulty in applying complex numerical models to the entire coastal strip (150 km), the researcher opted for a two-phase strategy. First of all, he identified the areas most at risk by using the Basque KOSTASystem videometric network operated by AZTI which enables the behaviour of beaches in the event of storms to be constantly and precisely monitored, among other purposes.

Once the areas most exposed to flooding, such as Zarautz, Itzurun or Gaztetape, were located, advanced numerical models were applied to develop specific warning systems. "We wanted the system to be precise and in Zarautz, for example, we achieved an 86% accuracy rate during the study period", highlights the researcher.

The system, which combines hydrodynamic data (waves and sea level) with information on beach morphology and coastal protection structures, enables the impact of storms to be anticipated, thus facilitating management decisions, such as closing access to the most exposed areas of the beach or reinforcing/implementing protection measures. "When there are very severe storms, the shape of the beach is of little consequence, but in more moderate storms, the morphology is key to fine-tune the warnings", stresses Abalia.

Furthermore, this system can be a useful tool to assess the influence of climate change on flooding, by considering sea level rise in the application of the tool. "This is important as it can help prepare for future scenarios", points out the researcher.

"The thesis and the Urban Klima 2050 project share the same goal: building a coast that is more resilient to climate change", says Abalia. One of the next steps is to transfer the warning system to other beaches identified as flood-prone, a process that will require case-specific adjustments and validation.