TIME-EVOLUTION OF COASTAL FLOODING UNCERTAINTIES USING GLOBAL SENSITIVITY ANALYSIS: INSIGHTS FROM OREWA BEACH, NEW ZEALAND

Coastal flooding is caused by the combined effect of a variety of oceanographic processes that cause a rise in seawater levels, eventually leading to the breach of natural and man-made coastal defences like beaches, dunes, and coastal vegetation, as well as sea walls, revetments, and dikes. When combined with the expansion of coastal urbanisation, the negative effects of flooding events are exacerbated, impacting both environmental and socio- economic landscapes. To aid with adaptation, coastal scientists have worked over the past decades to develop predictions for future coastal flooding scenarios. Diverse methodologies, models, and datasets have been employed, each influenced by numerous variables. However, at present, the uncertainty associated to each variable is still unknown. Therefore, understanding the role of such uncertainties is critical for prioritizing research on those components that will have a larger effect and so for developing more accurate models. In this work, we applied a variance-based global sensitivity analysis to estimate the contributing uncertainty in total water levels by sea level rise, astronomical tide, storm surge and runup dynamics, both historically and until 2099. The study area is Orewa, New Zealand, a beach that is already suffering the consequences of coastal flooding and beach erosion