|
|
 |
 |
 |
 |
|
IPCC Fourth Assessment Report: Climate Change 2007 |
|
 |
|
 |
|
|
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability 1.3.3.1 Changes in coastal geomorphology Sea-level rise over the last 100 to 150 years is probably contributing to coastal erosion in many places, such as the East Coast of the USA, where 75% of the shoreline removed from the influence of spits, tidal inlets and engineering structures is eroding (Leatherman et al., 2000; Daniel, 2001; Zhang et al., 2004) (Table 1.4; see Table SM1.4 for observations of changes in storm surges, flood height and areas, and waves). Over the last century, 67% of the eastern coastline of the UK has retreated landward of the low-water mark (Taylor et al., 2004).
Table 1.4. Changes in coastal processes. | Type of change | Observed changes | Period | Location | References |
|---|
| Shoreline erosion | 75% of shoreline, uninfluenced by inlets and structures, is eroding | mid-1800s to 2000 | East Coast USA | Zhang et al., 2004 | | Shoreline retreat, 0.61 m/yr | 1855-2002 | Louisiana, USA | Penland et al., 2005 | | Shoreline retreat, 0.94 m/yr | 1988-2002 | | | | Beach erosion prevalent due to sea-level rise, mangrove clearance | 1960s-1990s | Fiji | Mimura and Nunn, 1998 | | Beach erosion due to coral bleaching, mangrove clearance, sand mining, structures | 1950s-2000 | Tropics: SE Asia, Indian Ocean, Australia, Barbados | Wong, 2003 | | 19% of studied shoreline is retreating, in spite of land uplift, due to thawing of permafrost | 1950-1995 | Manitounuk Strait, Canada | Beaulieu and Allard, 2003 | | Shoreline erosion, recent acceleration | Pre-1990s to present | Estuary and Gulf of St. Lawrence, Canada | Bernatchez and Dubois, 2004; Forbes et al., 2004 | | Increased thermokarst erosion due to climate warming | 1970-2000 rela-tive to 1954-1970 | Arctic Ocean, Beaufort Sea coasts, Canada | Lantuit and Pollard, 2003 | | Beach erosion due to dams across the Nile and reduced river floods due to precipitation changes | Late 20th century | Alexandria, Egypt | Frihy et al., 1996 | | Coastal erosion | 1843-present | UK coastline | Taylor et al., 2004 | | Wetland changes | About 1,700 ha of degraded marshes became open water; non-degraded marshes decreased by 1,200 ha | 1938-1989 | Chesapeake Bay, USA | Kearney et al., 2002 | | Decreases in salt marsh area due to regional sea-level rise and human impacts | 1920s-1999 | Long Island, NY; Connecticut, USA | Hartig et al., 2002; Hartig and Gornitz, 2004 | | Salt marshes keep up with sea-level rise with sufficient sediment supply | 1880-2000 | Normandy, France | Haslett et al., 2003 | | Landward migration of cordgrass (Spartina alterniflora) due to sea-level rise and excess nitrogen | 1995-1999; late 20th century | Rhode Island, USA | Donnelly and Bertness 2001; Bertness et al., 2002 | | | | | | | Decrease from 12,000 to 4,000 ha, from land reclamation, wave-induced erosion and insufficient sediment | 1919-2000 | Venice, Italy | Day et al., 2005 | | Seaward-prograding mudflats replacing sandy beaches, due to increased dredged sediment supply | 1897-1999 | Queensland coast, Australia | Wolanski et al., 2002 | | Wetland losses due to sea-level rise, land reclamation, changes in wind/wave energy, tidal dynamics | 1850s-1990s | Greater Thames Estuary, UK | van der Wal and Pye, 2004 | | Decreased rates of deltaic wetland progradation due to reduced sediment supply from dam construction | 1960s-2003 | Yangtze River Delta, Peoples Republic of China | Yang et al., 2005 | | Coastal vegetation changes | Grassy marshes replaced by mangrove due to sea-level rise, water table changes | 1940-1994 | South-east Florida, USA | Ross et al., 2000 | | Mangrove encroachment into estuarine wetlands due to changing water levels, increased nutrient load, and salt-marsh compaction during drought | 1940s-1990s | South-east Australia | Saintilan and Williams,1999; Rogers et al., 2006 |
In addition to sea-level change, coastal erosion is driven by other natural factors such as wave energy, sediment supply, or local land subsidence (Stive, 2004). In Louisiana, land subsidence has led to high average rates of shoreline retreat (averaging 0.61 m/yr between 1855 and 2002, and increasing to 0.94 m/yr since 1988) (Penland et al., 2005); further erosion occurred after Hurricanes Katrina and Rita in August 2005. These two hurricanes washed away an estimated 562 km2 of coastal wetlands in Louisiana (USGS, 2006). Climate variability also affects shoreline processes, as documented by shoreline displacement in Estonia associated with increasing severe storms and high surge levels, milder winters, and reduced sea-ice cover (Orviku et al., 2003). Significant sections of glacially rebounding coastlines, which normally would be accreting, are nonetheless eroding, as for example along Hudson Bay, Canada (Beaulieu and Allard, 2003). Reduction in sea-ice cover due to milder winters has also exacerbated coastal erosion, as in the Gulf of St. Lawrence (Bernatchez and Dubois, 2004; Forbes et al., 2004). Degradation and melting of permafrost due to climate warming are also contributing to the rapid retreat of Arctic coastlines in many regions, such as the Beaufort and Laptev Sea coasts (Forbes, 2005). Anthropogenic activities have intensified beach erosion in many parts of the world, including Fiji, Trinidad and parts of tropical Asia (Mimura and Nunn, 1998; Restrepo et al., 2002; Singh and Fouladi, 2003; Wong, 2003). Much of the observed erosion is associated with shoreline development, clearing of mangroves (Thampanya et al., 2006) and mining of beach sand and coral. Sediment starvation due to the construction of large dams upstream also contributes to coastal erosion (Frihy et al., 1996; Chen et al., 2005b; Georgiou et al., 2005; Penland et al., 2005; Syvitski et al., 2005b; Ericson et al., 2006). Pumping of groundwater and subsurface hydrocarbons also enhances land subsidence, thereby exacerbating coastal erosion (Syvitski et al., 2005a). |
|
|
|