Downscaled projections of regional wave climate inherit this uncertainty and are highly variable, especially for Pacific regions directly impacted by ENSO and on sub-annual timescales (Mori et al., 2013, Hemer et al., 2013). There remains considerable uncertainty in the prediction of future shifts in ENSO behaviour from Global Climate Modelling (GCM) because of the non-linearity of ENSO and complex coupled feedbacks (Watanabe et al., 2012). Our methods provide a second-order approach to project coastal response and predict the discrete shoreline rotations for ENSO flavours. Results indicate that shoreline response to ENSO in most headland-bay beach coasts is not as simple as the existing paradigm that (anti-) clockwise rotation occurs during El Niño (La Niña). We show that the alongshore variability in beach morphological type can be used to model the static equilibrium planform response for each ENSO phase. Morphodynamic modelling in a headland-bay beach indicates that CP ENSO leads to higher coastal erosion potential and slower post-storm recovery than EP ENSO during an El Niño/La Niña cycle. This is because variability in trade wind wave generation is masked in deepwater by the persistence of high power extra-tropical waves that have reduced impact on nearshore processes due to high wave refraction. We also show that coastal change between CP and EP ENSO cannot be inferred from shifts in the deepwater wave climate. The modulation of the trade wind wave climate during CP ENSO has thus far been neglected in existing coastal process studies. We show that CP ENSO events produce different patterns of directional wave power to EP ENSO along the southeast Australian shelf and southwest Pacific region, because of significant variability in trade-wind wave generation. Wave climate and Pacific basin coastal behaviour associated with El Niño Southern Oscillation (ENSO) is understood at a reconnaissance level, but the coastal response to different central Pacific (CP) versus eastern Pacific (EP) flavours of ENSO is unknown.

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