Non‐Stationary Probabilistic Tsunami Hazard Assessments Compounding Tides and Sea Level Rise.

Tides are often the largest source of sea levels fluctuations. Two new probabilistic tsunami hazard assessments (PTHA) methods are proposed to combine the tidal phase uncertainty at the moment of tsunami occurrence with other sources of uncertainty. The first method adopts a Stochastic Reduced Order Model (SROM) producing sets of tidal phase samples to be used in tsunami simulations. The second method uses tsunami simulations with prescribed collocation tidal phases and tide probability distributions to model the uncertainty. The methods are extended to non‐stationary probabilistic tsunami hazard assessment, compounding tsunamis, tides and sea level rise (SLR). As an illustration, these methods are applied for assessing tsunamis generated in the Manila Subduction Zone, on the coasts of Kao Hsiung and Hong Kong. While the SROM‐based method is faster solving for the PTHA if only tides are considered, the collocation‐based method is faster when both SLR and tides are considered. For the illustration case, tides have a relevant impact on PTHA results, however, the SLR within an exposure time of 100 years has stronger impact. PTHA curves of the maximum tsunami elevation are affected by tides and SLR differently. While tides and SLR increase the dispersion of PTHA hazard curve distributions, the latter also produces a translation toward higher elevations. The development of formulations based on SROM or collocation tides is the key to establishing a method which feasibly can be applied to other regions for comprehensive analysis at a global scale. Plain Language Summary: Tsunami hazards can be evaluated using a probabilistic tsunami hazard assessment (PTHA) approach which determines probabilities of exceeding a certain tsunami intensity. A relevant source of uncertainty in PTHA are tides. Tsunamis striking the coast may have different impacts depending on whether they arrive at high or low tide. Moreover, the exposed infrastructure may last many decades and climate‐change‐driven sea‐level‐rise would compound tsunamis and tides, making the hazard worse. We develop two PTHA methods incorporating tides. The first method uses a stochastic reduced order model (SROM). The second method uses sets of tsunami simulations with same tide, known as collocation tidal phases. Both methods aim to estimate tsunami uncertainties and can be also used for non‐stationary probabilistic tsunami hazard assessment which combines tsunamis, tides and sea level rise (SLR). The new methods are applied into an illustration case in South China Sea. The method based on SROM is fastest solving the PTHA with tides. Though, the collocation‐based method is fastest solving for the nPTHA with tides and SLR. While the impact of tides is relevant in PTHA and nPTHA results, SLR produces a greater effect in the studied ports. The conclusions are site‐specific. Key Points: A Stochastic Reduced Order Model (SROM)‐based method and a collocation‐based method incorporating tides and sea level rise (SLR) are evaluated for tsunami hazard assessmentsThe collocation‐based method provides accurate results compared to the SROM‐based methodThe impact of tides and SLR on tsunami intensities depends on the tidal range and SLR within the exposure time, respectively [ABSTRACT FROM AUTHOR]