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Multi-decadal shoreline change in coastal natural world heritage sites – a global assessment

Multi-decadal shoreline change in coastal natural world heritage sites – a global assessment
Multi-decadal shoreline change in coastal natural world heritage sites – a global assessment
Natural World Heritage Sites (NWHS), which are of Outstanding Universal Value, are increasingly threatened by natural and anthropogenic pressures. This is especially true for coastal NWHS, which are additionally subject to erosion and flooding. This paper assesses shoreline change from 1984 to 2016 within the boundaries of 67 designated sites, providing a first global consistent assessment of its drivers. It develops a transferable methodology utilising new satellite-derived global shoreline datasets, which are classified based on linearity of change against time and compared with global datasets of geomorphology (topography, land cover, coastal type, and lithology), climate variability and sea-level change. Significant shoreline change is observed on 14% of 52 coastal NWHS shorelines that show the largest recessional and accretive trends (means of −3.4 m yr−1 and 3.5 m yr−1, respectively). These rapid shoreline changes are found in low-lying shorelines (<1 m elevation) composed of unconsolidated sediments in vegetated tidal coastal systems (means of −7.7 m yr−1 and 12.5 m yr−1), and vegetated tidal deltas at the mouth of large river systems (means of −6.9 m yr−1 and 11 m yr−1). Extreme shoreline changes occur as a result of redistribution of sediment driven by a combination of geomorphological conditions with (1) specific natural coastal morphodynamics such as opening of inlets (e.g. Río Plátano Biosphere Reserve) or gradients of alongshore sediment transport (e.g. Namib Sea) and (2) direct or indirect human interferences with natural coastal processes such as sand nourishment (e.g. Wadden Sea) and damming of river sediments upstream of a delta (e.g. Danube Delta). The most stable soft coasts are associated with the protection of coral reef ecosystems (e.g. Great Barrier Reef) which may be degraded/destroyed by climate change or human stress in the future. A positive correlation between shoreline retreat and local relative sea-level change was apparent in the Wadden Sea. However, globally, the effects of contemporary sea-level rise are not apparent for coastal NWHS, but it is a major concern for the future reinforcing the shoreline dynamics already being observed due to other drivers. Hence, future assessments of shoreline change need to account for other drivers of coastal change in addition to sea-level rise projections. In conclusion, extreme multi-decadal linear shoreline trends occur in coastal NWHS and are driven primarily by sediment redistribution. Future exacerbation of these trends may affect heritage values and coastal communities. Thus shoreline change should be considered in future management plans where necessary. This approach provides a consistent method to assess NWHS which can be repeated and help steer future management of these important sites.
Accretion, Coastal heritage, Conservation, Erosion, Local and global scales, Multi-decadal, Recession, Sea-level rise, Shoreline change, UNESCO, World natural heritage sites
1748-9326
Sabour, Salma
dae16302-03bf-4a88-aea8-e1fdacdfa8b3
Brown, Sally
dd3c5852-78cc-435a-9846-4f3f540f2840
Nicholls, Robert J
4ce1e355-cc5d-4702-8124-820932c57076
Haigh, Ivan D
945ff20a-589c-47b7-b06f-61804367eb2d
Luijendijk, Arjen P
13bfb5aa-a279-4f7f-b20d-abdf5ab96925
Sabour, Salma
dae16302-03bf-4a88-aea8-e1fdacdfa8b3
Brown, Sally
dd3c5852-78cc-435a-9846-4f3f540f2840
Nicholls, Robert J
4ce1e355-cc5d-4702-8124-820932c57076
Haigh, Ivan D
945ff20a-589c-47b7-b06f-61804367eb2d
Luijendijk, Arjen P
13bfb5aa-a279-4f7f-b20d-abdf5ab96925

Sabour, Salma, Brown, Sally, Nicholls, Robert J, Haigh, Ivan D and Luijendijk, Arjen P (2020) Multi-decadal shoreline change in coastal natural world heritage sites – a global assessment. Environmental Research Letters, 15 (10), [104047]. (doi:10.1088/1748-9326/ab968f).

Record type: Article

Abstract

Natural World Heritage Sites (NWHS), which are of Outstanding Universal Value, are increasingly threatened by natural and anthropogenic pressures. This is especially true for coastal NWHS, which are additionally subject to erosion and flooding. This paper assesses shoreline change from 1984 to 2016 within the boundaries of 67 designated sites, providing a first global consistent assessment of its drivers. It develops a transferable methodology utilising new satellite-derived global shoreline datasets, which are classified based on linearity of change against time and compared with global datasets of geomorphology (topography, land cover, coastal type, and lithology), climate variability and sea-level change. Significant shoreline change is observed on 14% of 52 coastal NWHS shorelines that show the largest recessional and accretive trends (means of −3.4 m yr−1 and 3.5 m yr−1, respectively). These rapid shoreline changes are found in low-lying shorelines (<1 m elevation) composed of unconsolidated sediments in vegetated tidal coastal systems (means of −7.7 m yr−1 and 12.5 m yr−1), and vegetated tidal deltas at the mouth of large river systems (means of −6.9 m yr−1 and 11 m yr−1). Extreme shoreline changes occur as a result of redistribution of sediment driven by a combination of geomorphological conditions with (1) specific natural coastal morphodynamics such as opening of inlets (e.g. Río Plátano Biosphere Reserve) or gradients of alongshore sediment transport (e.g. Namib Sea) and (2) direct or indirect human interferences with natural coastal processes such as sand nourishment (e.g. Wadden Sea) and damming of river sediments upstream of a delta (e.g. Danube Delta). The most stable soft coasts are associated with the protection of coral reef ecosystems (e.g. Great Barrier Reef) which may be degraded/destroyed by climate change or human stress in the future. A positive correlation between shoreline retreat and local relative sea-level change was apparent in the Wadden Sea. However, globally, the effects of contemporary sea-level rise are not apparent for coastal NWHS, but it is a major concern for the future reinforcing the shoreline dynamics already being observed due to other drivers. Hence, future assessments of shoreline change need to account for other drivers of coastal change in addition to sea-level rise projections. In conclusion, extreme multi-decadal linear shoreline trends occur in coastal NWHS and are driven primarily by sediment redistribution. Future exacerbation of these trends may affect heritage values and coastal communities. Thus shoreline change should be considered in future management plans where necessary. This approach provides a consistent method to assess NWHS which can be repeated and help steer future management of these important sites.

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Accepted/In Press date: 26 May 2020
Published date: 30 September 2020
Keywords: Accretion, Coastal heritage, Conservation, Erosion, Local and global scales, Multi-decadal, Recession, Sea-level rise, Shoreline change, UNESCO, World natural heritage sites

Identifiers

Local EPrints ID: 444770
URI: http://eprints.soton.ac.uk/id/eprint/444770
ISSN: 1748-9326
PURE UUID: 449a9b4f-c240-4999-884e-4234826ab93b
ORCID for Sally Brown: ORCID iD orcid.org/0000-0003-1185-1962
ORCID for Robert J Nicholls: ORCID iD orcid.org/0000-0002-9715-1109

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Date deposited: 04 Nov 2020 17:31
Last modified: 18 Feb 2021 17:11

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