World - An assessment of whether long-term global changes in waves and storm surges have impacted global coastlines
"We conclude that the available datasets do not show clear forcing/response linkages between long-term shoreline change and changes in waves and storm surge over the past three decades."
Ghanavati, M., Young, I., Kirezci, E. et al. An assessment of whether long-term global changes in waves and storm surges have impacted global coastlines. Sci Rep13, 11549 (2023). https://doi.org/10.1038/s41598-023-38729-y
Abstract
A common inference in research studies of observed and projected changes in global ocean wave height and storm surge, is that such changes are potentially important for long-term coastal management. Despite numerous studies of the impacts of anthropogenic climate change on trends in global wind and waves, a clear link to impacts on sandy coastlines, at global scale, is yet to be demonstrated. This study presents a first-pass assessment of the potential link between historical trends in global wave and storm surge values and recession/progradation rates of sandy coastlines since the 1980s. Global datasets of waves, surge and shoreline change rate are used for this purpose. Over the past 30 + years, we show that there have been clear changes in waves and storm surge at global scale. The data, however, does not show an unequivocal linkage between trends in wave and storm surge climate and sandy shoreline recession/progradation. We conclude that these long-term changes in oceanographic parameters may still be too small to have a measurable impact on shoreline recession/progradation and that primary drivers such as ambient imbalances in the coastal sediment budget may be masking any such linkages.
Introduction
Being home to between 10 to 13% of the global population, the low elevation coastal zone (LECZ: coastal land zone at less than 10 m above mean sea level) is arguably the most inhabited land zone in the world1. Close to one third (31%) of the global coastline is classified as sandy coastlines2, which are very dynamic systems, changing at a multitude of spatio-temporal scales in response to local oceanographic drivers such as waves, tides, storm surges and sea level rise, as well as in response to terrestrial drivers (e.g. fluvial sediment loads) and human activities (e.g. engineering structures, land reclamations). Climate change, and associated mean sea level rise, is projected to result in widespread coastal recession along sandy coasts through the twenty-first century3, potentially disrupting lives and leading to massive socio-economic losses4,5. Therefore, adequately understanding how climate change may affect sandy coastlines is of great importance. Although, some first-pass projections of how sandy shorelines may change over the twenty-first century are now available4,6,7, these estimates have been obtained using simplistic models that facilitated global scale assessments. Currently available data sets of sandy shoreline change (recession/progradation) and associated oceanographic drivers (sea level rise, waves, storm surges) over the last few decades do, however, lend themselves to a more detailed historical analysis of the potential forcing-response linkages between oceanographic drivers of sandy shoreline change, at global scale. Such an analysis constitutes the focus of the present study.
In recent years, significant research has focused on studies of historical long-term variability of ocean wave climate, including trends of wave height and storm frequency both at the global and regional scale8,9,10,11,12,13,14,15,16. Several studies have also focused on regional and global trends in storm surge level, intensity and frequency17,18,19,20,21,22,23. The global climate and hence winds, waves, and storm surge change at multiple scales. Muti-decadal oscillations (e.g. El Niño) are known to influence wind and wave conditions and have also been shown to impact coastal erosion24,25,26. The above studies also show that long-term anthropogenic changes in climate give rise to trends in winds and waves. It is often claimed that these long-term changes in ocean wave climate and extremes may potentially have impacts on coastal ecosystems, sandy beach recession, evolution and beach alignment5,16,27,28,29,30,31,32. If this is the case, future changes in wave and storm surge conditions, could be projected to impact beaches. Despite the many claims of a potential link between changing wave and surge conditions and sandy shoreline change, to our knowledge, no study has ever been undertaken to determine whether there is, in fact, a measurable link between historical sandy shoreline recession/progradation trends and wind waves and storm surge trends, at global scale.
In the following, we use the terminology recession/progradation to respectively describe the shoreward/seaward movement of the mean beach location averaged over a long period of time (here 3 decades). This can be contrasted with erosion/accretion which are associated with short-term changes in shoreline position as a result of individual storms or medium-term changes in weather patterns (e.g. El Niño)24.
In this paper, we combine data from a variety of global and regional datasets to examine trends in recent decades in wave and surge parameters at coastal locations, globally. These are compared with satellite derived recession/progradation rates at sandy beaches over the same period. It should be noted that the purpose of this study is to investigate if there is a clear linkage between long term trends in wave and storm surge conditions and rates of recession/progradation over three decades, rather than shorter-term shoreline changes. Global data for wave parameters (wave energy flux, wave height, wave period, wave direction and number of extreme wave events) and storm surge (surge level and number of storm surge events) at coastal locations are considered, using available global datasets. Also, to add more detail and to validate the use of global-scale deep water wave model data, a high-resolution regional dataset of wave conditions for southern Australia is used. The historical recession/progradation of sandy beaches is determined using two satellite derived global datasets. A regional recession/progradation dataset for the Australian coastline is used for further validation. Finally, potential linkages between long-term changes in oceanic waves, storm surge and sandy shoreline recession/progradation are investigated at global-scale.
