Tsunami waves are often described as travelling long distances with little loss of energy. Yet, as they approach the coast, this picture changes: vegetation, rough seabeds, and coastal structures begin to dissipate wave energy in ways that are still not fully understood.
The paper “Obstacle-induced dissipation of tsunami waves: linking solitary-wave and N-wave formulations”, published in npj Natural Hazards (available on https://www.nature.com/articles/s44304-026-00192-w), revisits this long-standing problem from a different perspective. Rather than introducing a new model, the study focuses on clarifying why existing approaches can lead to different predictions under the same physical conditions.
A key aspect highlighted in the paper is that two elements are often implicitly combined: how the wave is represented (for example, as a solitary wave or a tsunami-like N-wave), and how energy dissipation is modelled. By explicitly separating these components within a common shallow-water framework, the paper enables a consistent comparison between different formulations.
Within this framework, the paper shows that solitary waves and tsunami-like N-waves share the same underlying structure of amplitude decay, which follows a hyperbolic law. Differences between waveforms arise not from the type of decay, but from a coefficient linked to waveform geometry.
The analysis is supported by laboratory experiments in which solitary waves propagate through arrays of rigid cylinders representing idealized vegetation. These experiments are used to calibrate bulk drag coefficients, which are then applied—without re-fitting—to tsunami-like waveforms. This provides a consistent basis for comparing different waveform representations and dissipation closures.
The results indicate that, for identical obstacle configurations, predicted attenuation depends primarily on the adopted dissipation model. In particular, constant-rate formulations, which lead to exponential decay, tend to overestimate attenuation when applied to finite tsunami-like pulses.
By making modelling assumptions more explicit, the paper provides a clearer framework for interpreting wave attenuation in vegetated coastal environments. This is particularly relevant for applications such as tsunami hazard assessment and the evaluation of nature-based coastal protection strategies.