Abstract
Changes in coastal morphology have broad consequences for the sustainability of coastal communities, structures and ecosystems. Although coasts are monitored locally in many places, understanding long-term changes at a global scale remains a challenge. Here we present a global and consistent evaluation of coastal morphodynamics over 32 years (1984–2015) based on satellite observations. Land losses and gains were estimated from the changes in water presence along more than 2 million virtual transects. We find that the overall surface of eroded land is about 28,000 km2, twice the surface of gained land, and that often the extent of erosion and accretion is in the order of km. Anthropogenic factors clearly emerge as the dominant driver of change, both as planned exploitation of coastal resources, such as building coastal structures, and as unforeseen side effects of human activities, for example the installment of dams, irrigation systems and structures that modify the flux of sediments, or the clearing of coastal ecosystems, such as mangrove forests. Another important driver is the occurrence of natural disasters such as tsunamis and extreme storms. The observed global trend in coastal erosion could be enhanced by Sea Level Rise and more frequent extreme events under a changing climate.
Highlights
Coastal environments form the interface between the land and sea or ocean
Exploiting the extensive monitoring capabilities of satellites[29,30], here we developed a global-scale and consistent database of coastal morphodynamics, valid for any type of shore
This study is based on the Global Surface Water Explorer (GSWE) dataset, a global database derived from the analysis of over 3 million satellite images that maps water presence over 32 years[29]
Summary
Coastal environments form the interface between the land and sea or ocean. They host key infrastructures, ecosystems and about 40% of the world’s global population[1,2]. These studies are generally characterized by high resolution data for rather small areas Their local character, together with the use of different measures of change (e.g. cross-shore lengths referred to different estimated coastlines, or surfaces, or surface per year of erosion/accretion) and differing space-time settings, hamper their use for comparative analyses. Because these techniques are demanding in terms of manpower, equipment and costs, it is difficult to deploy them at larger scales. The remainder of this paper is structured as follows: in Section 2 the results are summarized; in Section 3 the results are discussed, examining extreme and noticeable cases of erosion/accretion and relating these with known drivers of coastal morphodynamics; in Section 4 the conclusions drawn from the study are presented
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