A novel statistical approach to predict seasonal high tide flooding

Abstract

Sea level rise is increasing the frequency of high tide flooding in coastal communities across the United States. Although the occurrence and severity of high-tide flooding will continue to increase, skillful prediction of high tide flooding on monthly-to-annual time horizons is lacking in most regions. Here, we present an approach to predict the daily likelihood of high tide flooding at coastal locations throughout the U.S. using a novel probabilistic modeling approach that relies on relative sea-level rise, tide predictions, and climatological non-tidal residuals as measured by NOAA tide gauges. The structure of the model will also enable future incorporation of mean sea level anomaly predictions from numerical, statistical, and machine learning forecast systems. A retrospective skill assessment using the climatological sea level information indicates that this approach is skillful at 61 out of 92 NOAA tide gauges where at least 10 high tide flood days occurred from 1997–2019. In this case, a flood day occurs when the observed water level exceeds the gauge-specific high tide flood threshold. For these 61 gauges, on average 35% of all floods are accurately predicted using this model, with over half of the floods accurately predicted at 18 gauges. The corresponding False-Alarm-Rate is less than 10% for all 61 gauges. Including mean sea level anomaly persistence at leads of 1 and 3 months further improves model skill in many locations, especially the U.S. Pacific Islands and West Coast. Model skill is shown to increase substantially with increasing sea level at nearly all locations as high tides more frequently exceed the high tide flooding threshold. Assuming an intermediate amount of relative sea level rise, the model will likely be skillful at 93 out of the 94 gauges projected to have regular flooding by 2040. These results demonstrate that this approach is viable to be incorporated into NOAA decision-support products to provide guidance on likely high tide flooding days. Further, the structure of the model will enable future incorporation of mean sea level anomaly predictions from numerical, statistical, and machine learning forecast systems.

The Global Drivers of Chronic Coastal Flood Hazards Under Sea‐Level Rise

“…In other words, the larger TR at Funafuti results in a lower annual maximum number of surge-driven flood days even though ESS values are the same at both locations. Similar tidal modulation in flood probability during different times of year at the same site was described by Dusek et al (2022). We subsequently focus on how tidal modulation affects flood frequencies between sites.…”

“…For example, San Juan (top left, Figure 5) has a maximum number of minor surge-driven flood days per year (35) that is more than twice that of Funafuti (13; center left Figure 5), despite both locations having the same ESS value (0.12 m). This finding can be explained by combining the demonstrated independence between tides and skew surges at most locations (Santamaria-Aguilar & Vafeidis, 2018;Williams et al, 2016), and daily flooding probabilities (Dusek et al, 2022). For a skew surge of 0.12 m to cause (surge-driven) minor flooding, the highest tide of the day must be within 0.12 m of the flood threshold (Dusek Hague et al, 2022).…”

“…These estimated flood thresholds are referred to as common impact thresholds. The use of these thresholds is now standard practice in regional and national coastal flood hazard studies in the US (Dusek et al., 2022; Ghanbari et al., 2019; Gold et al., 2022; Li et al., 2022, 2021; Thompson et al., 2021), despite their limitations (e.g., Section 4.2). Most recently, this approach has been used to estimate flood thresholds in China (Li et al., 2023).…”

“…In this study, we use the concept of freeboard to identify how high water levels must be to cause flooding of a specific severity (Ghanbari et al., 2019; Hague et al., 2022; Sweet & Park, 2014). Mathematically, freeboard is the vertical distance between a flood level and some measure of high tide (Figure 1c; Dusek et al., 2022; Hague et al., 2022; Ritman et al., 2022). Here we adopt the highest astronomical tide (HAT), the highest tide in the 20‐year tidal analysis, as this measure of high tide, following Hague et al.…”

“…Recent increases in global mean sea level have been sufficient to allow impactful floods to occur without large storm surges (Hague et al., 2020; Ray & Foster, 2016; Sweet et al., 2016). Accordingly, many locations now experience most of their minor coastal floods during benign weather conditions (Dusek et al., 2022; Hague et al., 2022; Ritman et al., 2022).…”