Shoreline changes interpreted from multi-temporal aerial photographs and high resolution satellite images: Wotje Atoll, Marshall Islands

Wotje Atoll is located at 9°25′N and 170°04′E within the Republic of the Marshall Islands in the central Pacific Ocean. As on other atolls, the islands perched along the rim of Wotje are low-lying and considered highly vulnerable to the impacts of climate change. A widely anticipated impact of continued sea level rise is the chronic erosion of island shorelines. Using a combination of aerial photographs and satellite imagery shoreline changes are assessed over a 67-year period characterized by rising sea level. Results indicate that between 1945 and 2010 shoreline accretion is more prevalent than erosion, with an average Net Shoreline Movement (NSM) of + 1.74 m, indicating accretion. Shorelines were accretionary along the lagoon, ocean and channel facing shorelines, as well as on elongate spits and small islands. A high-frequency assessment of shoreline change on a subset of islands in the east of Wotje reveals that islands were stable, with a balance between shoreline accretion and erosion. Shorelines interpreted from high resolution satellite imagery captured between 2004 and 2012 indicate that shorelines within this sample of islands are largely in an erosive state. The post-2004 shift toward erosion may be sea level rise induced, or part of an unresolved shoreline oscillation. This study demonstrates the critical need for improved shoreline change monitoring within atoll settings in order to assess sea level rise impacts along island shorelines.