Using global sensitivity analysis to evaluate the uncertainties of future shoreline changes under the Bruun rule assumption

International audienceFuture sandy shoreline changes are often assed by summing the contributions of longshore and cross-shore effects.In such approaches, a contribution of sea-level rise can be incorporated by adding a supplementary term based onthe Bruun rule. Here, our objective is to identify where and when the use of the Bruun rule can be (in)validated, inthe case of wave-exposed beaches with gentle slopes. We first provide shoreline change scenarios that account forall uncertain hydrosedimentary processes affecting the idealized low- and high-energy coasts described by Stive(2004)[Stive, M. J. F. 2004, How important is global warming for coastal erosion? an editorial comment, ClimaticChange, vol. 64, n 12, doi:10.1023/B:CLIM.0000024785.91858. ISSN 0165-0009]. Then, we generate shorelinechange scenarios based on probabilistic sea-level rise projections based on IPCC. For scenario RCP 6.0 and 8.5and in the absence of coastal defenses, the model predicts an observable shift toward generalized beach erosionby the middle of the 21st century. On the contrary, the model predictions are unlikely to differ from the currentsituation in case of scenario RCP 2.6. To get insight into the relative importance of each source of uncertainties, wequantify each contributions to the variance of the model outcome using a global sensitivity analysis. This analysisshows that by the end of the 21st century, a large part of shoreline change uncertainties are due to the climatechange scenario if all anthropogenic greenhousegas emission scenarios are considered equiprobable. To conclude,the analysis shows that under the assumptions above, (in)validating the Bruun rule should be straightforwardduring the second half of the 21st century and for the RCP 8.5 scenario. Conversely, for RCP 2.6, the noise inshoreline change evolution should continue dominating the signal due to the Bruun effect. This last conclusion canbe interpreted as an important potential benefit of climate change mitigation