1.3.3.3 Changes in storm surges, flood heights and areas, and waves

The vulnerability of the coastal zone to storm surges and waves depends on land subsidence, changes in storminess, and sea-level rise (see Supplementary Material). Along the North American East Coast, although there has been no significant long-term change in storm climatology, storm-surge impacts have increased due to regional sea-level rise (Zhang et al., 2000). The U.S. Gulf Coast is particularly vulnerable to hurricane surges due to low elevation and relative sea-level rise (up to 1 cm/yr along parts of the Louisiana coast), only part of which is climate-related (Penland et al., 2005). Hurricane Katrina, in August 2005, generated surges over 4 m, with catastrophic consequences (NOAA, 2005). In Venice, Italy, the frequency of surges has averaged around 2 per year since the mid-1960s, compared with only 0.19 surges per year between 1830 and 1930, with land subsidence, which was exacerbated by groundwater pumping between 1930 and 1970 (Carminati et al., 2005), and expanded sea-lagoon interactions (due to channel dredging) playing a greater role than global sea-level rise (Camuffo and Stararo, 2004). Surges have shown a slight decrease in Brittany, France, in recent decades, largely due to changes in wind patterns (Pirazzoli et al., 2004).

Apparent global increases in extreme high water levels since 1975 are related to mean sea-level rise and to large-scale inter-decadal climate variability (Woodworth and Blackman, 2004). Wave height increases have been documented in the north-east Atlantic Ocean (Woolf et al., 2002), along the US Pacific North-west coast (Allan and Komar, 2006) and in the Maldives (Woodworth and Blackman, 2004), but decreases have been found in some areas of the Mediterranean from 1958 to 2001 (Lionello, 2005; Lionello and Sanna, 2005).