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.
Highlights
World Heritage Sites are locations of Outstanding Universal Values (OUV) selected by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as having cultural, historical, scientific, or other forms of significance [1]
This study comprises the first global assessment of multi-decadal shoreline change from 1984 to 2016 within coastal Natural World Heritage Sites (NWHS) asking: ‘how are coastal NWHS shorelines changing around the world and why?’
Based on newly available open-access datasets, shoreline change was analysed for 67 NWHS worldwide, in terms of linear behaviour, recessional or accretive trends, and potential drivers of change
Summary
World Heritage Sites are locations of Outstanding Universal Values (OUV) selected by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as having cultural, historical, scientific, or other forms of significance [1]. The UNESCO World Heritage Centre established a list of 14 primary factors of deterioration of the OUV ranging from human activities (development, pollution, social and cultural use), climate change and severe weather events, to invasive species, management and institutional factors [4]. 88 NWHS intersect the coast and include sites most at risk from climate change [8] They have pristine environments, their coastlines are increasingly subject to anthropogenic pressures inside and outside their boundaries such as pollution, population growth, and development including port facilities, dams and pumping stations. The OUV of about two thirds of coastal NWHS are at high to very high threat from deteriorating factors These sites are subject to physical processes such as sea-level rise (SLR) [10–14] and human modifications to sediment budgets [15]. As sites that have very limited internal anthropogenic disturbance, they present significant opportunities to analyse how and why shorelines change due to natural drivers and/or external pressures
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