An Extreme Value Analysis (EVA) of Extreme Sea-Level (ESL) Events in Hawai‘i to Evaluate the Hawai‘i Sea-Level Rise Vulnerability and Adaptation Report

Abstract

The Hawai‘i Climate Commission’s 2017 Hawai‘i Sea-Level Rise Vulnerability and Adaptation Report (Report) currently underestimates the potential effects of sea-level rise (SLR) on the frequency and intensity of three main hazards Hawai‘i presently faces: coastal erosion, passive flooding, and high wave flooding. SLR may influence the severity and threat of flooding, in particular from nontidal, episodic weather events (e.g., hurricanes, tropical cyclones, storm surges, and tsunamis). However, the Hawai‘i Climate Commission omits these event-based coastal flooding events from their Report because they are currently considered infrequent events. I perform Extreme Value Analysis (EVA) using the Generalized Pareto Distribution (GPD) and Peaks-Over-Threshold (POT) approaches on daily maximum sea-level records for different tide gauge stations in Hawai‘i (Hilo, Honolulu, Kahului, Mokuoloe, and Nawiliwili) in order to determine whether excluding tsunami events significantly impact: [1] the distribution (𝜉) of ESL events, which are instances where water heights exceed a specific critical threshold value (μ), (2) the number (𝜆) of annual exceedances of μ, and [3] the recurrence and return levels of ESL events. By proving that tsunami events influence 𝜉, 𝜆, and return curves of ESL events in Hawai‘i, this thesis motivates future studies on how other nontidal, episodic weather events may potentially impact ESL events. In particular, I hope to persuade the Hawai‘i Climate Commission to consider how the frequency and intensity of event-based coastal flooding events will change with SLR, so they can develop a more comprehensive state-wide assessment and thereby plan accordingly to protect coastal communities in Hawai‘i against SLR-related hazards.