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PROPERTY AGEMENT MAN PROGRAM

Coastal Region Systems Coasts are dynamic systems, undergoing adjustments of form and process (termed morphodynamics) at different time and space scales in response to geomorphological and oceanographical factors (Cowell et al., 2003a,b). Human activity exerts additional pressures that may dominate over natural processes. Often models of coastal behaviour are based on palaeoenvironmental reconstructions at millennial scales and/or process studies at sub-annual scales (Rodriguez et al., 2001; Storms et al., 2002; Stolper et al., 2005). Adapting to global climate change, however, requires insight into processes at decadal to century scales, at which understanding is least developed (de Groot, 1999; Donnelly et al., 2004). Coastal landforms, affected by short-term perturbations such as storms, generally return to their pre-disturbance morphology, implying a simple, morphodynamic equilibrium. Many coasts undergo continual adjustment towards a dynamic equilibrium, often adopting different ‘states’ in response to varying wave energy and sediment supply (Woodroffe, 2003). Coasts respond to altered conditions external to the system, such as storm events, or changes triggered by internal thresholds that cannot be predicted on the basis of external stimuli.

COORDINATING LEAD AUTHORS: Robert J. Nicholls (UK), Poh Poh Wong (Singapore). LEAD AUTHORS: Virginia Burkett (USA), Jorge Codignotto (Argentina), John Hay (New Zealand), Roger McLean (Australia), Sachooda Ragoonaden (Mauritius), Colin D. Woodroﬀe (Australia) CONTRIBUTING AUTHORS: Pamela Abuodha (Kenya), Julie Arblaster (USA/Australia), Barbara Brown (UK), Don Forbes (Canada), Jim Hall (UK), Sari Kovats (UK), Jason Lowe (UK), Kathy McInnes (Australia), Susanne Moser (USA), Susanne Rupp-Armstrong (UK), Yoshiki Saito (Japan), Richard S.J. Tol (Ireland) REVIEW EDITORS: Job Dronkers (The Netherlands), Geoﬀ Love (Australia), Jin-Eong Ong (Malaysia)

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COASTAL REGION AREA

COASTAL REGION MAP

COASTAL REGION SYSTEM

Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.eralPoh Poh Wong (Singapore)

Introduction: scope, summary of processes. Often models of coastal behaviour Third Assessment Report concluare based on palaeoenvironmental reconsions and key issues structions at millennial scales and/or process studies at sub-annual scales (Rodriguez et al., This chapter presents a global perspective on 2001; Storms et al., 2002; Stolper et al., 2005). the impacts of climate change and sea-level Adapting to global climate change, however, rise on coastal and adjoining lowlying areas, requires insight into processes at decadal with an emphasis on post-2000 insights. to century scales, at which understanding is Here, coastal systems are considered as least developed (de Groot, 1999; Donnelly the interacting low-lying areas and shallow et al., 2004). Coastal landforms, affected by coastal waters, including their human comshort-term perturbations such as storms, ponents (Figure 6.1). This includes adjoining generally return to their pre-disturbance coastal lowlands, which have often develmorphology, implying a simple, morphooped through sedimentation during the dynamic equilibrium. Many coasts undergo Holocene (past 10,000 years), but excludes the continental shelf and ocean margins (for marine ecosystems see Chapter 4). Inland seas are not covered, except as analogues. In addition to local drivers and interactions, coasts are subject to external events that pose a hazard to human activities and may compromise the natural functioning of coastal systems (Figure 6.1). Terrestrial-sourced hazards Figure 1. Climate change and the coastal system showing the major climate change factors, including external marine and terrestrial influences. include river floods and inputs of sediment or continual adjustment towards a dynamic pollutants; marine-sourced hazards include equilibrium, often adopting different ‘states’ storm surges, energetic swell and tsunamis. in response to varying wave energy and Natural coastal systems sediment supply (Woodroffe, 2003). Coasts Coasts are dynamic systems, undergoing respond to altered conditions external to the adjustments of form and process (termed system, such as storm events, or changes morphodynamics) at different time and triggered by internal thresholds that cannot space scales in response to geomorphologbe predicted on the basis of external stimuli. ical and oceanographical factors (Cowell et This natural variability of coasts can make al., 2003a,b). Human activity exerts additional it difficult to identify the impacts of climate pressures that may dominate over natural change. For example, most beaches world-

Examples of extreme water level simulations for impact studies Although inundation by increases in mean sea level over the 21st century and beyond will be a problem for unprotected low-lying areas, the most devastating impacts are likely to be associated with changes in extreme sea levels resulting from the passage of storms (e.g., Gornitz et al., 2002), especially as more intense tropical and extra-tropical storms are expected (Meehl et al., 2007). Simulations show that future changes are likely to be spatially variable, and a high level of detail can be modelled (see also Box 11.5 in Christensen et al. (2007). Figures 6.4 and 6.5 are based on barotropic surge models driven by climate change projections for two ﬂood-prone regions. In the northern Bay of Bengal, simulated changes in storminess cause changes in extreme water levels.

When added to consistent relative sea-level rise scenarios, these result in increases in extreme water levels across the Bay, especially near Kolkata (Figure 6.4a). Around the UK, extreme high sea levels also occur. The

Figure 2. Increases in the height (m) of the 50-year extreme water level. In the northern Bay of Bengal under the IS92a climate scenario in 2040-2060 (K – Kolkata (Calcutta), C – Chittagong) (adapted from Mitchell et al., 2006).

largest change near London has important implications for ﬂood defence (Figure 6.4b; Dawson et al., 2005; Lavery and Donovan, 2005). Figure 6.5 shows the change in ﬂooding due to climate change for Cairns

Figure 3. Flooding around Cairns, Australia during the >100 year return-period event under current and 2050 climate conditions based on a 2xCO2 scenario. The road network is shown in black (based on McInnes et al., 2003).