Abstract
Inlet-interrupted sandy coasts are dynamic and complex coastal systems with continuously evolving geomorphological behaviors under the influences of both climate change and human activities. These coastal systems are of great importance to society (e.g., providing habitats, navigation, and recreational activities) and are affected by both oceanic and terrestrial processes. Therefore, the evolution of these inlet-interrupted coasts is better assessed by considering the entirety of the Catchment-Estuary-Coastal (CEC) systems, under plausible future scenarios for climate change and increasing pressures due to population growth and human activities. Such a holistic assessment of the long-term evolution of CEC systems can be achieved via reduced-complexity modeling techniques, which are also ably quantifying the uncertainties associated with the projections due to their lower simulation times. Here, we develop a novel probabilistic modeling framework to quantify the input-driven uncertainties associated with the evolution of CEC systems over the 21stcentury. In this new approach, probabilistic assessment of the evolution of inlet-interrupted coasts is achieved by (1) probabilistically computing the exchange sediment volume between the inlet-estuary system and its adjacent coast, and (2) distributing the computed sediment volumes along the inlet-interrupted coast. The model is applied at three case study sites: Alsea estuary (United States), Dyfi estuary (United Kingdom), and Kalutara inlet (Sri Lanka). Model results indicate that there are significant uncertainties in projected volume exchange at all the CEC systems (min-max range of 2.0 million cubic meters in 2100 for RCP 8.5), and the uncertainties in these projected volumes illustrate the need for probabilistic modeling approaches to evaluate the long-term evolution of CEC systems. A comparison of 50thpercentile probabilistic projections with deterministic estimates shows that the deterministic approach overestimates the sediment volume exchange in 2100 by 15–30% at Alsea and Kalutara estuary systems. Projections of coastline change obtained for the case study sites show that accounting for all key processes governing coastline change along inlet-interrupted coasts in computing coastline change results in projections that are between 20 and 134% greater than the projections that would be obtained if only the Bruun effect were taken into account, underlining the inaccuracies associated with using the Bruun rule at inlet-interrupted coasts.
Highlights
The coastal zone is the dynamic link that connects the land and oceans and has always attracted human settlement because of its multiple uses, rich bio-diversity and resources
Where VT is the cumulative change in the total sediment volume exchange between the estuary and its adjacent coast, VBI is the sediment demand of the basin due to sea-level rise-driven change in basin volume, VBV is the change in basin volume due to variation in river discharge, and VFS is the change in fluvial sediment supply due to combined effects of climate change and anthropogenic activities, with all volumes in m3
The results highlight that the deterministic projections of VT for Representative Concentration Pathway (RCP) 8.5 presented in Bamunawala et al (2020) are consistently greater than the 50th percentile values of the probabilistic projections, by as much as
Summary
The coastal zone is the dynamic link that connects the land and oceans and has always attracted human settlement because of its multiple uses, rich bio-diversity and resources. Due to predicted population growth, economic development and urbanization, human pressures on coasts and coastal ecosystems will very likely increase significantly over the 21st century, with over 1 billion people expected to live in the coastal zone by 2050 (Hugo, 2011; Wong et al, 2014; Merkens et al, 2016). In conjunction with rising sea level, regional changes in wave and storm conditions and increased river flows will likely result in more frequent and intense episodic coastal flooding (Ranasinghe, 2016). Forced migration due to sea-level rise driven coastline recession over this century is expected to cost about 1 trillion USD (Hinkel et al, 2013) while the potential economic losses in coastal cities due to flooding are expected cost more than 1 trillion USD by 2050 (Hallegatte et al, 2013)
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