Atmospheric storm surge modeling methodology along the French (Atlantic and English Channel) coast

Abstract

Storm surge modeling and forecast are the key issues for coastal risk early warning systems. As a general objective, this study aims at improving high-frequency storm surge variations modeling within the PREVIMER system (www.previmer.org), along the French Atlantic and English Channel coasts. The paper focuses on (1) sea surface drag parameterization and (2) uncertainties induced by the meteorological data quality. The modeling is based on the shallowwater version of the model for applications at regional scale (MARS), with a 2-km spatial resolution. The model computes together tide and surge, allowing properly taking into account tide-surge interactions. To select the most appropriate parameterization for the study area, a sensitivity analysis on sea surface drag parameterizations is done, based on comparisons of modeled storm surges (extracted with a tidal component analysis) with four tidal gauges, during four storm events, and over about 7.5 years, where the observed water level is processed in the same way as the modeling results. The tested drag parameterizations are a constant one, as reported by Moon et al. (J Atmos Sci 61: 2321-2333, 2007, Makin (BoundLayer Meteorol 115: 169-176, 2005), and Charnock (J Roy Meteor Soc 81: 639-640, 1955). Charnock's parameterization, either constant with high value (0.022) or relying on a full statistical description of the sea state, enables to improve storm surges forecast with peak errors 10 cm smaller than those computed with the other drag coefficient formulations. The impact of the meteorological forcing quality is evaluated over January 2012 from the comparison between surges modeled with different meteorological data (ARPEGE, ARPEGE High Resolution and AROME) and observations. For event time scale, storm surge computation is highly improved with ARPEGE High Resolution data. For month time scale, statistics of model accuracy are less sensitive to the choice of meteorological forcing. As a conclusion, the Charnock's parameterization is advised to model storm surges on the French Atlantic and English Channel coasts, whereas the quality requirements regarding meteorological inputs depend on the time scale of interest. Within the PREVIMER system, aiming at forecasting events, ARPEGE High Resolution data are used.

Tide and skew surge independence: New insights for flood risk

“…These result primarily from seasonally varying winds, atmospheric pressures, and steric effects [Pugh and Woodworth, 2014]. Seasonal stratification on the continental shelf can modulate the barotropic M 2 tide by typically 5-10% [Muller et al, 2014] through its effect on vertical mixing. At Lerwick the winter months contain some of the largest predicted HW (Figure 4).…”

Evaluating uncertainties of future marine flooding occurrence as sea-level rises

“…For example, accurate information on storm surges or vertical ground motions can be obtained, but at the cost of complex geophysical investigations and oceanographic studies (e.g. Brooks et al, 2007;Muller et al, 2014;Le Roy et al, 2014;Bulteau et al, 2015). Hence, the desire to maximize the social impact of future applied research raises the following questions: what is the relative importance of each source of uncertainty in the final flooding projections?…”

On the consistency of the drag between air and water in meteorological, hydrodynamic and wave models

“…Janssen et al (2002) show that coupling the wind and waves improves the prediction of both wind velocities in the atmospheric boundary layer and wave parameter values. Muller et al (2014) show that also the prediction of surges improves when a variable Charnock coefficient, depending on a statistical description of the sea state, is taken into account.…”