Large regional variability in coastal erosion caused by ENSO

Abstract

In the Pacific Basin, El Niño/Southern Oscillation (ENSO) is the dominant mode of interannual climate variability and drives substantial changes in oceanographic forcing, likely having a significant impact on Pacific coastlines. Yet, how sandy coasts respond to these basin-scale changes has to date been limited to a few long-term beach monitoring sites, predominantly on developed coasts. Here we use 35 years of Landsat imagery to map shoreline variability around the Pacific Rim (72,000 beach transects) and identify coherent patterns of beach erosion and accretion controlled by ENSO. We find that approximately one third of all beaches experience significant erosion during El Niño phases, with the Eastern Pacific particularly vulnerable to widespread erosion (most notably during the large 1997/1998 event). In contrast, La Niña events coincide with significant accretion for approximately one quarter of all beaches, although conversely drives substantial erosion in south-east Australia and other localized regions. The significant regional variability in coastal response to ENSO should be considered in light of future projected intensification and shifts in ENSO amplitudes and flavors.

Primary drivers of multidecadal spatial and temporal patterns of shoreline change derived from optical satellite imagery

“…Dodet et al, 2019). The recent work of Vos et al (2022) is a notable exception, where SDS anomaly around the Pacific Basin was computed during extreme (El Niño/Southern Oscillation) ENSO index phases (multivariate index larger than half of its standard deviation). The authors found significant and coherent regional variability in coastal response to ENSO.…”

Morphodynamics of wave-dominated beaches

“…Such data sets are generally not collected at the temporal scale (< 10 years) and resolution (monthly) commensurate with beach morphodynamics, which can change from day to day [e.g., during storms Almar et al, 2010] and can display decadal variability due to hemispheric-scale fluctuations in the wave climate [ e.g., Masselink et al, 2014;Barnard et al, 2017;Dodet et al]. Global satellite data sets going back to the 1980s are beginning to be analysed to explore hemispheric-scale climate forcing of beach change [Vos et al, 2022], and the availability of high-resolution geostationary satellite data also opens new perspectives by increasing data frequency and reducing satellite-derived products uncertainties.…”

Improving multi-decadal coastal shoreline change predictions by including model parameter non-stationarity

“…An average beach slope was used in line with previous studies on satellite-derived shorelines, where using a time-evolving beach slope did not result in better shoreline mapping (Castelle et al, 2021). The reader is referred to Vos et al (2021) for further details on this dataset.…”