Multi-decadal coastal evolution of remote Pacific islands: armouring of Taha’a, Raiatea, Maupiti, and Rangiroa (French Polynesia)

International audienceCoastal urbanisation is not constrained only to heavily industrialised cities. It has reached the coastlines of French Polynesia islands (South Pacific). In the context of climate change–induced cyclones and storms, sea level rise, and ecosystem damage, characterising the evolution and current extent of man-made structures along coastlines is of key importance for managers. In French Polynesia, three high volcanic islands (Taha’a, Raiatea, Maupiti) and one atoll (Rangiroa) were selected as case studies to highlight the increasing extent of artificial coastal structures in a tropical setting. Using high-resolution aerial imagery from the mid-twentieth century and from recent years, changes in coastal typology were assessed. The proportion of natural coastlines decreased from over 90% to under 40% within seven decades on the volcanic islands, mostly due to a boom in private embankments. This decrease was more limited in Rangiroa (93 to 89%), possibly due to its different morphological characteristics and coastal protection requirements. Based on these changes, for more sustainable management of island coasts, we recommend adopting case-by-case policies to rectify past and current management and urban planning strategies, especially relating to private embankments