Sea Surges in Camargue: Trends over the 20th century.

Continental Shelf Research 27 (2007) 922–934 Sea surges in Camargue: Trends over the 20th century A. Ullmanna,b,, P.A. Pirazzolic, A. Tomasind,e aUFR des Sciences Ge´ographiques et de l’Ame´nagement, Universite´ d’Aix-Marseille I, Aix en -Provence, France bCEREGE—UMR 6635, Aix en Provence, France cCNRS-Laboratoire de Ge´ogrphie Physique, 1 place Aristide Briand, 92 195-Meudon, France dCNR-ISMAR, Venezia, Italy eUniversita` di Venezia, Venezia, Italy Received 8 November 2005; received in revised form 24 November 2006; accepted 4 December 2006 Available online 25 January 2007 Abstract The vulnerability to short-term and long-term sea-level rises is particularly high in subsiding deltaic areas, especially in microtidal seas, when surges (the differences between the observed sea heights and the simultaneous astronomical tide) are frequent. At the Grau-de-la-Dent tide-gauge in the Camargue (Rhone delta, France), daily sea-level records are available since 1905. Hourly tide data spanning the period 1979–1995 were obtained through the digitisation of the original paper records: the local harmonic constants and the surges for the whole 20th century have been computed from these hourly observations. It appears that the annual maximum observed sea-level height increases by 4 mm/yr at a rate that is two times faster than the average observed relative sea level. The increasing trend of the annual maximum positive sea surges (+1.9 mm/yr), which is equal to the average relative sea-level rise, is thus responsible for this difference. The most important meteorological factor associated with local sea-surge occurrences is wind blowing from 1001 to 1201 sectors, which tends to push the water toward the coasts. Since 1961, the frequency and the speed of wind from this sector increased, although with some variability, thus contributing in part to the increase in the frequency and intensity of the surges. Due to the changing hydrodynamics phenomenon in the Camargue, a positive feedback mechanism between extreme marine events and shoreline regression is another factor to explain the sea-surge rise over the long term. The increase in sea-surge frequency and height during the last century is especially of concern in the deltaic area if the nearfuture global sea-level rise predicted by climate models is also taken into account. r 2007 Elsevier Ltd. All rights reserved. Keywords: Sea level; Surge; Tide; Wind; Flooding risk; Camargue; Rhone delta 1. Introduction Any rise in sea level will have adverse impacts such as coastal erosion and flooding, depending on the time scale and the magnitude of the rise and the human response to it (Paskoff, 1993). A rise in sea level may be due to several factors acting on various time scales, i.e., atmospheric storms (Bouligand and Pirazzoli, 1999; Pirazzoli, 2000; Trigo and Davies, 2002; Pirazzoli and Tomasin, 2002), river flooding in estuaries (Svensson and Jones, 2002), but also land sinking or similar non climate-related changes, linked to sediment compaction, isostasy, coastal geomorphologic evolutions or urban development. ARTICLE IN PRESS www.elsevier.com/locate/csr 0278-4343/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2006.12.001 Corresponding author. CEREGE, Europoˆ le Me´diterrane´en de l’Arbois, B.P 80, 13545 Aix-en-Provence, France. E-mail address: ullmann@cerege.fr (A. Ullmann).