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- Title
The Global Drivers of Chronic Coastal Flood Hazards Under Sea‐Level Rise.
- Authors
Hague, Ben S.; McGregor, Shayne; Jones, David A.; Reef, Ruth; Jakob, Doerte; Murphy, Bradley F.
- Abstract
We present the first global estimates of annual average exceedances of contemporary minor, moderate, and major flood levels under sea‐level rise (SLR). Applying established methods, we show that minor flooding will occur most days worldwide under 0.7 m global SLR. Moderate flooding occurs at the same frequency under 1.0 m SLR. Local and regional differences in flood threshold elevations, tidal ranges, and non‐tidal variability lead to differences in the SLR required for this chronic flooding to emerge. Lower flood thresholds, smaller tidal ranges, and larger extreme skew surges mean chronic flooding can emerge with less SLR. We discuss several implications of these findings for coastal flood hazard assessments. First, tide‐driven water level variability dominates weather‐driven water level variability when determining locations' propensities for frequent and chronic flooding under SLR. Second, centimeter‐accurate flood threshold information is necessary to accurately estimate present and future flood hazards. Third, locations with the most frequent floods at present may not be those that have the most frequent floods under SLR. We develop the Rapid Assessment Framework for Frequent Flood Transitions under SLR (RAFFFTS) to apply these findings to locations not previously considered in global coastal flood hazard studies. RAFFFTS can robustly identify potential future tidal flooding hotspots using only 1‐year observational records. We anticipate RAFFFTS will be a valuable tool for identifying locations at risk of chronic flooding under SLR, complementing existing tools for identifying changes in less frequent episodic floods. Plain Language Summary: Sea‐level rise (SLR) is leading to coastal floods becoming more frequent than in the past with floods occurring multiple times per year at many locations around the world. Here, we present the first estimates of how frequently present‐day minor, moderate, and major flood levels will be exceeded under SLR using a globally consistent approach. We show that floods that currently occur annually will occur hundreds of days per year under amounts of SLR projected to occur this century in most locations. However, some locations will see much more rapid increases in flood rates than others. We develop an easy‐to‐use framework that can accurately predict how much SLR is needed for these rapid increases to occur at a particular location, based primarily on local tidal ranges. Locations with smaller differences between low and high tide elevations are most susceptible to rapid increases in flood rates. Once floods of any severity become annual occurrences, tides are the most important physical process that modulates how flood hazards respond to further SLR. We explore the implications of our findings for coastal flood hazard assessment and decision‐making. Key Points: Exceedances of present‐day minor, moderate, and major flood levels will become chronic events globally with less than 1 m of sea‐level rise (SLR)Annual coastal flood days under SLR can be robustly estimated from local flood levels, tidal ranges, and skew surge magnitudesFuture chronic coastal flood hotspots will likely differ from present‐day coastal flood hotspots and future episodic coastal flood hotspots
- Subjects
ABSOLUTE sea level change; STORM surges; FLOOD warning systems; FLOODS; WATER levels; FLOOD risk; RISK assessment; REGIONAL differences
- Publication
Earth's Future, 2023, Vol 11, Issue 8, p1
- ISSN
2328-4277
- Publication type
Article
- DOI
10.1029/2023EF003784