Downscaling Changing Coastlines in a Changing Climate: The Hybrid Approach

Abstract

Shifts in the frequency of typical meteorological patterns in an ocean basin, over interannual to decadal time scales, cause shifts in the patterns of wave generation. Therefore, ocean basin‐scale climate shifts produce shifts in the wave climates affecting the coastlines of the basin. We present a hybrid methodology for downscaling observed (or predicted) climate shifts into local nearshore wave climates and then into the associated coastline responses. A series of statistical analyses translate observed (or predicted) distributions of meteorological states into the deep water wave climate affecting a coastal region and dynamical modeling combined with statistical analyses transform the deep water wave climate into the nearshore wave climate affecting a particular coastline. Finally, dynamical modeling of coastline evolution hindcasts (or predicts) how coastline shapes respond to climate shifts. As a case study, we downscale from meteorological hindcast in the North Atlantic basin since 1870 to the responses of the shape of the coast of the Carolinas, USA. We test the hindcasts using shoreline change rates calculated from historical shorelines, because shifts in coastline shape equate to changes in the alongshore pattern of shoreline change rates from one historical period to another. Although limited by the availability of historical shorelines (and complicated by historical inlet openings), the observations are consistent with the predicted signal of ocean basin‐scale climate change. The hybrid downscaling methodology, applied to the output of global climate models, can be used to help forecast future patterns of shoreline change related to future climate change scenarios.

Predicting Climate‐Driven Coastlines With a Simple and Efficient Multiscale Model

“…Interpolation functions are trained from the offshore boundary wave climate series to reconstruct continuous hourly wave climate series at a depth relevant to the shoreline change modeling (in this study 20‐m water depth). The methodology has been previously applied in other long‐term morphological studies (Antolínez et al, ). Further details on the hybrid nearshore wave propagation are given in Appendix ).…”

“…High‐LST gradients can quickly produce large impacts such as inlet closures (Ranasinghe & Pattiaratchi, ), rapid build‐up of ebb/flood shoals (Oertel, ), headland bypassing of large volumes of sand (Kristensen et al, ; Storlazzi & Field, ), and rotation of pocket beaches and changes in curvature (Harley et al, ; Ratliff & Murray, ). Persistent alongshore gradients in LST (even small gradients) can result in chronic impacts shaping our coastlines (Antolínez et al, ; Ashton et al, , ; Ashton & Murray, , ; Falqués et al, ; Idier et al, ; Kaergaard & Fredsoe, , ; Moore et al, ; Murray & Ashton, ).…”

“…These cycles are superimposed on an accelerating background climate change arising from human activities (IPCC, ). Each of these climate signals—the cycles and the trends—will tend to cause shifts in coastline position and planview shape (e.g., Antolínez et al, ; Coco et al, ; Davidson et al, ; Moore et al, ; Ruggiero, Buijsman, et al, ; Ruggiero et al, ; Vitousek, Barnard, & Limber, ). Accelerated sea level rise (SLR) is also occurring and the associated change in sediment transport patterns can lead to long‐term shoreline erosion (e.g., Bruun, ; Cowell, Stive, Niedoroda, Swift, et al, ; Cowell, Stive, Niedoroda, Vriend, et al, ; Moore et al, ; Ranasinghe & Stive, ; Wolinsky & Murray, ).…”

“…In this paper we present a novel shoreline evolution model (A COupled CrOss‐shOre, loNg‐shorE, and foreDune evolution model, COCOONED), which combines a hybrid nearshore propagation of offshore waves using a physics‐driven model, data mining and statistical methods following Antolínez et al (), and a process‐driven coastal model combining (1) longshore transport and shoreline change due to waves with a one‐line approach similar to Vitousek and Barnard (), (2) cross‐shore transport and equilibrium shoreline change due to waves and varying water levels (e.g., SLR, monthly sea level anomalies, and storm surge) using a modified version of the Miller and Dean () model, (3) FDE using a modified version of the model proposed by Mull and Ruggiero () based on Kriebel and Dean (), and (4) the inclusion of profile adjustment by sediment supply. With this model we account for the combined effects of waves, varying water levels, and sediment supply in shoreline and FDE covering a wide range of spatial and temporal scales, including sequencing and clustering of storm events, and seasonal, interannual, and decadal oscillations.…”

Marine climate variability based on weather patterns for a complicated island setting: The New Zealand case

“…Relating wave conditions to large-scale synoptic patterns has been used to describe and project wave climate variability in the North Atlantic (Camus et al, 2014b;Perez et al, 2015;Antolínez et al, 2018) and eastern pacific (Hegermiller et al, 2017a;Rueda et al, 2017b). In New Zealand, Coggins et al (2015) used the Kidson´s types (KT) to categorize the wave field surrounding the main islands.…”