In the recent decade, many global and regional sea‐level rise (SLR) projections have been published, which raises questions for users. Here, we present a series of strategies to help users to see the forest for the trees, by reducing the number of choices to be made. First, we use the similarities in the methodologies and contributing sources of the projections to group 82 projections from 29 publications into only 8 families. Second, we focus on the timing of reaching several global mean SLR thresholds, and the uncertainty therein, rather than the projected value in the year 2100. Finally, we combine the information on timing and families to define three categories which can support decision making. For global mean SLR up to 0.50 m the differences in timing are small, regardless of climate scenario or family, clearly indicating a timing window for adaptation decisions. For larger global mean SLR (0.75–1.00 m), the climate scenario becomes more important for the uncertainties in timing, but the SLR threshold will be crossed within a limited window of time, supporting adaptation decision making on the medium to long term. Beyond 1.00 m the differences between the families and climate scenario strongly determine the uncertainties in timing, and more information is needed, for instance using early warning signals, before decisions for adaptation can be made. We make recommendations on how each of these three categories, combined with the lead time and lifespan of adaptation options, can inform decisions on adaptation strategies using adaptation pathways planning.

Sediment produced on fringing coral reefs that is transported along the bed or in suspension affects ecological reef communities as well as the morphological development of the reef, lagoon, and adjacent shoreline. This study quantified the physical process contribution and relative importance of sea‐swell waves, infragravity waves, and mean currents to the spatial and temporal variability of sediment in suspension. Estimates of bed shear stresses demonstrate that sea‐swell waves are the key driver of the suspended sediment concentration (SSC) variability spatially (reef flat, lagoon, and channels) but cannot fully describe the SSC variability alone. The comparatively small but statistically significant contribution to the bed shear stress by infragravity waves and currents, along with the spatial availability of sediment of a suitable size and volume, is also important. Although intratidal variability in SSC occurs in the different reef zones, the majority of the variability occurs over longer slowly varying (subtidal) timescales, which is related to the arrival of large swell waves at a reef location. The predominant flow pathway, which can transport suspended sediment, consists of cross‐reef flow across the reef flat that diverges in the lagoon and returns offshore through channels. This pathway is primarily due to subtidal variations in wave‐driven flows but can also be driven alongshore by wind stresses when the incident waves are small. Higher frequency (intratidal) current variability also occurs due to both tidal flows and variations in the water depth that influence wave transmission across the reef and wave‐driven currents.

Rocky reef coastlines typically feature highly variable and often abrupt cross‐shore and alongshore changes in bathymetry. The effects of this irregular rocky bathymetry on the dynamics of infragravity waves are largely unknown. Most models of infragravity wave dynamics have been developed and validated on smooth alongshore‐uniform bathymetries, which may break down over these highly variable bathymetries. A 2 week field experiment was conducted on a rocky reef‐fringed beach to investigate how the variable bathymetry affects the spatial and temporal variability of infragravity waves. The height of short (sea‐swell) waves decreased over the shallow reef due to breaking, whereas the height of infragravity waves increased toward the shoreline. Both during a storm event (H_m0 = 2.3 m) and under moderate wave conditions (H_m0 = 1.0–1.8 m), the infragravity waves formed a persistent cross‐shore standing wave pattern along the entire shoreline, despite the irregular bathymetry. In addition, the alongshore components of infragravity waves refracted by the presence of the nearshore reef were observed to propagate in opposite directions up and down the coast resulting in a local alongshore standing wave pattern. Thus, the presence of highly variable nearshore bathymetry, which commonly occurs along rocky reef coastlines, may produce both cross‐shore and alongshore standing wave patterns.

This study demonstrates the skills of D-FLOW Flexible Mesh (FM) and SFINCS (Super-Fast INundation of CoastS) in combination with the Delft Dashboard Tsunami Toolbox to numerically simulate tsunami offshore propagation and inundation based on the example of the 2011 Tōhoku tsunami in Japan. Caused by a megathrust earthquake, this is one of the most severe tsunami events in recent history, resulting in vast inundation and devastation of the Japanese coast. The comparison of the simulated with the measured offshore water levels at four DART buoys located in the north-western Pacific Ocean shows that especially the FM but also the SFINCS model accurately reproduce the observed tsunami propagation. The inundation observed at the Sendai coast is well reproduced by both models. All in all, the model outcomes are consistent with the findings gained in earlier simulation studies. Depending on the specific needs of future tsunami simulations, different possibilities for the application of both models are conceivable: (i) the exclusive use of FM to achieve high accuracy of the tsunami offshore propagation, with the option to use an all-in-one model domain (no nesting required) and to add tsunami sediment dynamics, (ii) the combined use of FM for the accurate simulation of the tsunami propagation and of SFINCS for the accurate and time efficient simulation of the onshore inundation and (iii) the exclusive use of SFINCS to get a reliable picture of the tsunami propagation and accurate results for the onshore inundation within seconds of computational time. This manuscript demonstrates the suitability of FM and SFINCS for the rapid and reliable assessment of tsunami propagation and inundation and discusses use cases of the three model combinations that form an important base for tsunami risk management.