Influence of Climate Change on Bimodal Cross‐Shore Distributions of the Longshore Sediment Transport Rate and Current Velocity on a Dissipative Sandy Beach

Abstract Changes in waves and wind caused by climate change would induce changes in the cross‐shore distribution of the longshore sediment transport rate, which would lead to morphological changes on the updrift and downdrift sides of coastal structures. Therefore, the impacts of climate change on the cross‐shore distributions of the longshore sediment transport rate and the longshore current velocity, which induces sediment transport, were examined at a sandy beach in Japan using a one‐dimensional numerical model and 9‐year wave and wind data simulated at 2‐hr intervals for the present and future climates. Both the present‐climate distributions had northward and southward predominant values near the shore and offshore, respectively, as a result of the combination of the southerly and northerly waves. Under the RCP8.5 scenario, the distributions shifted southward in the nearshore region, even though the mean wave direction did not change. This occurred because the significant wave height of the southerly waves decreased more than that of the northerly waves under this scenario. In the offshore region, northward longshore sediment transport became predominant because the number of large southerly waves increased. The results obtained using the peak wave directions differed from those obtained using the mean wave directions. There was a significant shift in the distributions to the south, and the bimodal distributions became unimodal. Future changes in the distributions can be estimated using 1‐day interval data instead of 2‐hr interval data with an error of 30% in the nearshore region.