NEAMWave26 exercise in the NE Atlantic Ocean: an opportunity for a better preparedness and operational response to large tsunamis off the Iberian margin

Tsunami Warning Systems have been progressively developed over the past six decades, with significant expansion and improvement in the last 20 years, in the aftermath of the 2024 Indian Ocean tsunami. In the NE Atlantic and Mediterranean region (NEAM), five Tsunami Service Providers (TSPs) (Portugal, France, Italy, Greece, Turkey) are operating on a permanent basis, following recommendations of the IOC/UNESCO within the ICG/NEAM (Intergovernmental Coordination Group). Frequent exercises are necessary to ensure a high level of operation and preparedness. Every 2-3 years, ICG/NEAM organizes regional exercises, called NEAMWave. The NEAMWave26 exercise was conducted in March 2026 to test the TSPs’ warning chains and procedures at multiple operational levels. Five scenarios were designed across the NEAM region. The scenario built for the NE Atlantic is based on the 1755 Lisbon earthquake, with an estimated moment magnitude of approximately 8.5. This event triggered a catastrophic tsunami and remains the largest natural disaster in Europe in the last 500 years, in terms of loss of lives and destruction. We present here a detailed analysis of this scenario and the lessons learned from the NEAMwave26 exercise in the NE Atlantic. Using numerical modeling, we show how tsunami waves propagated across the NE Atlantic, generating hazard and threat levels, both at regional and local scales. The tsunami warning messages issued by two operating TSPs (CENALT, France, and IPMA, Portugal) are presented to illustrate the sequence of the operational procedures in response to tsunami threat in the NE Atlantic. Moreover, the exercise outcomes are analyzed in light of feedback from subscribers and local authorities to draw key lessons learned from this exercise.