Abstract. Sea-level rise due to anthropogenic climate change is projected not
only to exacerbate extreme events such as cyclones and storms but
also to cause more frequent chronic flooding occurring at high tides under
calm weather conditions. Chronic flooding occasionally takes place
today in the low-lying areas of the Petit Cul-de-sac marin (Guadeloupe, West
Indies, French Antilles). This area includes critical industrial and harbor and
major economic infrastructures for the islands. As sea level rises, concerns
are growing regarding the possibility of repeated chronic flooding events,
which would alter the operations at these critical coastal infrastructures
without appropriate adaptation. Here, we use information on past and future
sea levels, vertical ground motion, and tides to assess times of emergence of
chronic flooding in the Petit Cul-de-sac marin. For RCP8.5 (Representative Concentration Pathway 8.5; i.e., continued
growth of greenhouse gas emissions), the number of flood days is projected
to increase rapidly after the emergence of the process so that coastal
sites will be flooded 180 d a year within 2 decades of the onset of
chronic flooding. For coastal locations with the lowest altitude, we show
that the reconstructed number of floods is consistent with observations
known from a previous survey. Vertical ground motions are a key source of
uncertainty in our projections. Yet, our satellite interferometric
synthetic-aperture radar results show that the local variability in this
subsidence is smaller than the uncertainties in the technique, which we
estimate to be between 1 (standard deviation of measurements) and 5 mm/yr (upper
theoretical bound). Despite these uncertainties, our results imply that
adaptation pathways considering a rapid increase in recurrent chronic
flooding are required for the critical port and industrial and commercial
center of Guadeloupe. Similar processes are expected to take place in many
low-elevation coastal zones worldwide, including on other tropical islands.
The method used in this study can be applied to other locations,
provided tide gauge records and local knowledge of vertical ground motions
are available. We argue that identifying times of emergence of chronic
flooding events is urgently needed in most low-lying coastal areas, because
adaptation requires decades to be implemented, whereas chronic flooding
hazards can worsen drastically within years of the first event being
observed.
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