Twenty-first-century projections of shoreline change along inlet-interrupted coastlines

Abstract

Sandy coastlines adjacent to tidal inlets are highly dynamic and widespread landforms, where large changes are expected due to climatic and anthropogenic influences. To adequately assess these important changes, both oceanic (e.g., sea-level rise) and terrestrial (e.g., fluvial sediment supply) processes that govern the local sediment budget must be considered. Here, we present novel projections of shoreline change adjacent to 41 tidal inlets around the world, using a probabilistic, reduced complexity, system-based model that considers catchment-estuary-coastal systems in a holistic way. Under the RCP 8.5 scenario, retreat dominates (90% of cases) over the twenty-first century, with projections exceeding 100 m of retreat in two-thirds of cases. However, the remaining systems are projected to accrete under the same scenario, reflecting fluvial influence. This diverse range of response compared to earlier methods implies that erosion hazards at inlet-interrupted coasts have been inadequately characterised to date. The methods used here need to be applied widely to support evidence-based coastal adaptation.

Monitoring Coastline Changes of the Malay Islands Based on Google Earth Engine and Dense Time-Series Remote Sensing Images

“…Considering that the coastline will change because of natural factors, such as sedimentation, seawater erosion, global warming, and human-made factors (e.g., port construction, land reclamation, and marine engineering) [20,49,50], the coastline at different periods also may change. Great changes likely will occur.…”

Climate Change Induced Coastline Change Adjacent to Small Tidal Inlets

“…The general behaviour of STIs is a function of fluvial processes (e.g., fluvial sediment fluxes) and oceanic processes [e.g., wave driven longshore sediment transport (LST)], all of which are projected to change as a result of climate change (Ranasinghe et al, 2013;Duong et al, 2016). Several studies over the last decade or so have shown that climate change will lead to multiple impacts in STI environs, including a decrease in inlet stability, erosion of inlet-adjacent coasts, erosion of estuary margin shorelines, permanent or frequent inundation of low lying areas along estuary margins, estuarine eutrophication, and toxic algal blooms (Duong et al, 2017(Duong et al, , 2018Bamunawala et al, 2020aBamunawala et al, ,b, 2021.…”

Probabilistic projections of the stability of small tidal inlets at century time scale using a reduced complexity approach

“…Changes to the inlet or the adjacent coast could therefore impact some or all of these human activities, leading to substantial socio-economic losses, and in some situations, threaten the safety of coastal communities 8 – 10 . Several recent studies have shown that, due to climate change, such system changes are all but inevitable over the twenty-first century 13 , 14 , and effective adaptation strategies therefore need to be developed and implemented. To properly inform such adaptation strategies, long term (~ 50–100 years) projections of how inlets may change in future, including quantification of the uncertainty associated in these projections, are required.…”

“…Unlike uninterrupted coasts that are governed only by oceanic processes such as tides, waves and mean sea level (MSL), inlet-interrupted coasts are also governed by terrestrial processes such as riverflow and fluvial sediment 6 , 8 – 10 , 14 – 18 . Therefore, projected climate change driven variations in any of these drivers can lead to many negative physical impacts on inlet-interrupted coasts, such as shoreline retreat adjacent to the inlet, erosion of estuary margin shorelines, inundation of low lying areas along estuary margins, estuarine eutrophication, and toxic algal blooms etc 17 .…”

“…However, following the adaptation pathways philosophy 27 , 28 , knowledge of how systems evolve through time is necessary to be able to develop and implement the right adaptation strategies at the right times as we move along the twenty-first century. This would typically require continuous century scale model morphodynamic simulations of inlet-interrupted coasts, which have to date only been undertaken with physics based, reduced complexity models such as SMIC 10 or G-SMIC 8 , 9 , 14 . However, while these models are able to provide projections of shoreline change near inlets, they do not provide detailed information of the time evolution of inlet Type and stability, knowledge of which is essential for developing effective adaptation strategies for fragile STI systems.…”