Journal Article

Non‐Stationary Probabilistic Tsunami Hazard Assessments Incorporating Climate‐Change‐Driven Sea Level Rise

Winckler, Patricio, Haase, Jennifer S., Sepúlveda, Ignacio, Liu, Philip L.‐F., Grigoriu, Mircea

2021

Overview

We face a new era in the assessment of multiple natural hazards whose statistics are becoming alarmingly non‐stationary due to ubiquitous long‐term changes in climate. One particular case is tsunami hazard affected by climate‐change‐driven sea level rise (SLR). A traditional tsunami hazard assessment approach where SLR is omitted or included as a constant sea‐level offset in a probabilistic calculation may misrepresent the impacts of climate‐change. In this paper, a general method called non‐stationary probabilistic tsunami hazard assessment (nPTHA), is developed to include the long‐term time‐varying changes in mean sea level. The nPTHA is based on a non‐stationary Poisson process model, which takes advantage of the independence of arrivals within non‐overlapping time‐intervals to specify a temporally varying hazard mean recurrence rate, affected by SLR. The nPTHA is applied to the South China Sea (SCS) for tsunamis generated by earthquakes in the Manila Subduction Zone. The method provides unique and comprehensive results for inundation hazard, combining tsunami and SLR at a specific location over a given exposure time. The results show that in the SCS, SLR has a significant impact when its amplitude is comparable to that of tsunamis with moderate probability of exceedance. The SLR and its associated uncertainty produce an impact on nPTHA results comparable to that caused by the uncertainty in the earthquake recurrence model. These findings are site‐specific and must be analyzed for different regions. The proposed methodology, however, is sufficiently general to include other non‐stationary phenomena and can be exploited for other hazards affected by SLR. Plain Language Summary Assessing natural hazards that are made worse by climate change cannot use previous methods that assume that the average behavior is a good representation of the hazard. Here we show the effect of climate‐change‐driven sea level rise (SLR) on tsunami hazard, where the continuously increasing SLR cannot be represented by an average value. Higher sea levels produce several changes in the tsunami behavior, including an increase in the maximum tsunami water level and in the speed the tsunami propagates. We introduce a new method which incorporates the long‐term time‐varying changes in mean sea level. The method can be applied to other coastal hazards, such as storm surge and waves. The new method is applied to port cities in the South China Sea (SCS) for tsunamis generated by earthquakes in the Manila Subduction Zone. We determine the probability of flooding urban areas within 50 and 100 years. The hazard in SCS is significantly impacted by SLR when it rises by an amount comparable to the tsunami height for a tsunami with moderate likelihood. The effect is comparable to that caused by the estimated uncertainty in recurrence interval of the causative earthquake. These results, though, are site‐specific. Key Points The impact of sea level rise (SLR) on probabilistic tsunami hazard assessment (PTHA) depends on the exposure time and the relative magnitude of both phenomena For the probabilistic tsunami hazard assessment (PTHA) in South China Sea, the sea level rise (SLR) is as important as the uncertainty of the earthquake recurrence model Sea level rise (SLR) can change the tsunami propagation properties so probabilistic tsunami hazard assessment (PTHA) must include nonlinear effects in the tsunami behavior and inundation level

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Climate change / climate change driven sea level rise and tsunamis / Coasts / Deformation / Earthquakes / Flooding / Hazard assessment / Mean sea level / non‐stationary probabilistic tsunami hazard assessment (nPTHA) / Random variables / Sea level / Sea level changes / Sea level rise / Seismic activity / Statistical analysis / Subduction (geology) / thinned non‐stationary poisson process / Tsunami hazard / tsunami hazard in South China Sea / Tsunamis / Uncertainty / Weather hazards