Coevolution of Extreme Sea Levels and Sea‐Level Rise Under Global Warming

Abstract

Design of coastal defense structures like seawalls and breakwaters can no longer be based on stationarity assumption. In many parts of the world, an anticipated sea‐level rise (SLR) due to climate change will constitute present‐day extreme sea levels inappropriate for future coastal flood risk assessments since it will significantly increase their probability of occurrence. Here, we first show that global annual maxima sea levels (AMSLs) have been increasing in magnitude over the last decades, primarily due to a positive shift in mean sea level (MSL). Then, we apply non‐stationary extreme value theory to model the extremal behavior of sea levels with MSL as a covariate and quantify the evolution of AMSLs in the following decades using revised probabilistic sea‐level rise projections. Our analysis reveals that non‐stationary distributions exhibit distinct differences compared to simply considering stationary conditions with a change in location parameter equal to the amount of MSL rise. With the use of non‐stationary distributions, we show that by the year 2050 many locations will experience their present‐day 100‐yr return level as an event with return period less than 15 and 9 years under the moderate (RCP4.5) and high (RCP8.5) representative concentration pathways. Also, we find that by the end of this century almost all locations examined will encounter their current 100‐yr return level on an annual basis, even if CO2 concentration is kept at moderate levels (RCP4.5). Our assessment accounts for large uncertainty by incorporating ambiguities in both SLR projections and non‐stationary extreme value distribution parameters via a Monte Carlo simulation.

Variability Assessment of Global Extreme Coastal Sea Levels Using Altimetry Data

“…The only coastal region showing almost null increases (and low statistical robustness) was the northwestern coast of America. These results reinforce the findings from previous studies stating this to be the main driver of the changing ESLs due to climate change [11,80]. Moreover, MSLR very likely also explains the fact that we found significant trends (95% confidence level) in over 95% of the coastal units analyzed.…”

The Influence of Future Changes in Tidal Range, Storm Surge, and Mean Sea Level on the Emergence of Chronic Flooding

“…Changes in rainfall and streamflow may shift annual recurrence intervals from 0.01 to 1 in a small number of locations under high greenhouse gas emission scenarios (He et al., 2022; Hirabayashi et al., 2021). In contrast, sea‐level rise in the same scenario causes present‐day 1‐in‐100‐year coastal flood expected to occur annually virtually everywhere, and more than 100 days per year in many locations (Boumis et al., 2023; Fox‐Kemper et al., 2021; Hague et al., 2020; Taherkhani et al., 2020; Tebaldi et al., 2021). Hence, not explicitly considering freshwater influences on chronic flood hazards should not affect the robustness of this study's findings.…”

Nonlinear Interactions of Sea‐Level Rise and Storm Tide Alter Extreme Coastal Water Levels: How and Why?

“…Sea‐level rise (SLR) is accelerating, and given the current trajectory of warming, a rise in global mean sea‐level exceeding 1 m is possible during the 21st century (Dangendorf et al., 2019; IPCC, 2019; Palmer et al., 2020). This rise reduces the freeboard between high tidal datum and flood stage, which introduces uncertainties in flood risk allowances that need to be considered in coastal risk and adaptation assessments (Arns et al., 2017; Boumis et al., 2023a; Buchanan et al., 2016; Hunter, 2012; Nicholls et al., 2021). Currently, 250 million people live on a land below annual coastal flood levels; without protective measures; this number may reach 340 million by 2050 (Kulp & Strauss, 2019).…”