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The coastal zones of Small Island States are hotspots of human habitation and economic endeavour. In the Pacific region, as elsewhere, there are large gaps in understandings of the exposure and vulnerability of people in coastal zones. The 22 Pacific Countries and Territories (PICTs) are poorly represented in global analyses of vulnerability to seaward risks. We combine several data sources to estimate populations to zones 1, 5 and 10 km from the coastline in each of the PICTs. Regional patterns in the proximity of Pacific people to the coast are dominated by Papua New Guinea. Overall, ca. half the population of the Pacific resides within 10 km of the coast but this jumps to 97% when Papua New Guinea is excluded. A quarter of Pacific people live within 1 km of the coast, but without PNG this increases to slightly more than half. Excluding PNG, 90% of Pacific Islanders live within 5 km of the coast. All of the population in the coral atoll nations of Tokelau and Tuvalu live within a km of the ocean. Results using two global datasets, the SEDAC-CIESIN Gridded Population of the World v4 (GPWv4) and the Oak Ridge National Laboratory Landscan differed: Landscan under-dispersed population, overestimating numbers in urban centres and underestimating population in rural areas and GPWv4 over-dispersed the population. In addition to errors introduced by the allocation models of the two methods, errors were introduced as artefacts of allocating households to 1 km x 1 km grid cell data (30 arc-seconds) to polygons. The limited utility of LandScan and GPWv4 in advancing this analysis may be overcome with more spatially resolved census data and the inclusion of elevation above sea level as an important dimension of vulnerability.

Compare estimates of the numbers of people living within 1, 5, and 10 km from the coast in Pacific Island Countries and Territories (PICTs). These distances are somewhat arbitrary, but in the absence of generally agreed definitions of the ‘coastal zone’ and of more integrated analyses that include elevation above sea level, livelihood portfolios and other measure of exposure to the ocean, they provide a logical basis for the analyses. Three coastal zones at 1, 5, and 10 km were mapped onto every populated island for each PICT. People residing within 1 km were considered to live on the coast, those within 5 km included those who could still easily walk to the coast and 10 km, those who interact with coastal communities (e.g. in terms of access to markets or other activities) and who would be able to easily get to the coast with some form of transport. The two global datasets used to spatially distribute populations were the SEDAC-CIESIN Gridded Population of the World v4 and the Oak Ridge National Laboratory LandScan™. GPWv4 is a minimally modelled population dataset that uniformly distributes census data from their native enumeration areas. LandScan™ allocates population census data using dasymetric cartographic techniques relying on ancillary data such as land cover, roads, terrain slope, urban extent, and accessibility to model population density at 30 arc-second grid resolution within administrative boundaries. Both global datasets distributed populations within enumeration areas to 30 arc second cells (approximate 1 km2 at the Equator). The following protocol explains the workflow used to calculate the Coastal Population Estimates for PICTs. The protocol involves three main steps: Generation of 1, 5 and 10 km coastal buffers Spatial disaggregation of the census population datasets using one of the three methods based on data availability. This step is not applicable for the global population grids. Overlay the coastal buffer mask on the disaggregated population datasets and sum the population contained within the coastal buffers to calculate the percentage of the country’s population within each of the three coastal zones.