On the fore-reef (Fig. 6), typically, this ratio is always less than 1, with reductions in wave-orbital velocities of order 20–30% at these locations for SLR = 1 m. Conversely, on the reef flat, the ratio is strongly dependent on the global reef bathymetry, and the magnitude of the change varies according to the depth and width of the reef flat, i.e. changes in the wave dynamics vary reef by reef (Fig. 7). The largest changes in the wave dynamics tend to occur on shallower and narrower reefs, but changes are not monotonic, with the velocity switching between being greater or less than the baseline condition as width and depth vary. Changes are subtle and differ reef by reef. For example, for reefs at the same depth, SLR decreases wave-orbital velocities (Urms/Urms0 < 1) on narrow reefs, but increases wave-orbital velocities (Urms/Urms0 > 1) on wide reefs. However, a maximum in the ratio Urms/Urms0 is observed on shallower reefs, so on very wide reefs velocities reduce back toward the baseline. There are also significant differences in the response to SLR on rough and smooth reefs, with smooth reefs being influenced by SLR to a greater extent than rough reefs. This has implications for potential feedback between the reef ecology and the wave dynamics (see discussion). Further, there is interplay between the influence of depth, width and roughness in terms of the impact of SLR, such that rough reefs show virtually no change in the hydrodynamic conditions for certain bathymetry, while smooth reefs show no change on different bathymetry. Changes to the hydrodynamic environment can be very significant, with increases in wave-orbital velocities from the baseline condition of up to 50–200% for average wave conditions. During cyclonic conditions the pattern of change in the velocities for different bathymetry is very similar to that for average wave conditions (not shown) but the changes are magnified, with increases of up to 400% in wave-orbital velocity on shallow narrow reef flats at SLR = 1 m.