Projected Future Changes of Australian Boundary Currents—Insights From Dynamical Downscaling Simulations

Abstract

Australian boundary currents strongly influence regional circulation, ecosystems, and coastal environments, yet remain inadequately resolved in coarse‐resolution global climate models, especially along mid‐latitude coasts. To assess their future evolution, we examine boundary‐current changes under an intermediate‐emissions scenario with a 1/12° regional ocean model forced by ensemble‐mean climate‐change signals from Coupled Model Intercomparison Project Phases 6 (CMIP6), using the Australian Regional Ocean Downscaling (AUSROD) framework. The model realistically simulates the East Australian Current (EAC) and its extension, Leeuwin Current (LC), South Australian Current (SAC), and Flinders Current (FC) during 1993–2023, in close agreement with reanalysis and observations. Projections show a slight weakening of the EAC and a marked strengthening of its extension, consistent with enhanced positive wind‐stress curl over the South Pacific south of ∼30°S. LC weakening, associated with a reduced meridional sea‐level gradient, is primarily driven by intensified subsurface thermosteric expansion linked to Subantarctic Mode Water warming. Along southern Australia, the FC strengthens consistent with Sverdrup Balance response, while the SAC weakens in the west due to the reduced LC but shows little change in the east under intensified local westerlies. While the tendencies align with coarse‐resolution CMIP6 ensemble results, the downscaled projections resolve substantially finer spatial and vertical structures. This study provides a systematic, dynamically consistent projection of Australian boundary currents at the end of the 21st century and highlights the added value of dynamical downscaling for resolving coastal and shelf processes. The AUSROD framework is practical for application to other regions, offering reliable information for future adaptation.