Abstract
In addition to the tsunami hazard posed by distant great earthquakes, Rapa Nui (Easter Island), in the Southeast Pacific Ocean, is exposed to frequent and intense coastal storms. Here, we use sea-level records and field surveys guided by video and photographic footage to show that extreme sea levels at Rapa Nui occur much more frequent than previously thought and thus constitute an unrecognized hazard to the inland’s maritime supply chain. We found that extreme sea-level events, including the two most extreme (March 5th and May 5th, 2020) in our 17-month-long analyzed period (from January 1st, 2019, to May 31st, 2020), resulted from constructive superpositions of seiches on the shelf, storm surges and high tides. By further analyzing time series of atmospheric and wind-generated wave data, we conclude that these extreme sea levels are ultimately driven by the breaking of large waves near the coastline (i.e., wave setup), with lesser contribution of barometric setup and even less of wind setup. We also propose that these large waves were mainly generated from strong, long-lasting, NW winds associated with intense atmospheric rivers (long, narrow regions in the atmosphere that transport abundant water vapor) passing over Rapa Nui. Given that the intensity of atmospheric rivers and sea level are thought to increase as climate changes, a deeper understanding of the relation between meteorological and oceanographic processes at Rapa Nui is strongly needed.
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Data availability
All the used data is provided in the Acknowledgment Section.
Code availability
All calculations were done with regular mathematical software.
Notes
The integrated water vapor transport (IVT) is a vector that gauges the flux of moisture through the entire troposphere over a given grid box. Its zonal and meridional components are obtained by the vertical integration of uq and vq, where (u,v) are zonal and meridional wind and q is the water vapor mixing ratio (e.g., Viale et al. 2018).
Time zones Easter Island: UTC-5 in summer time (September-March) and UTC-6 in winter time (April–August).
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Acknowledgements
This work is dedicated to Lomito. We deeply thank Mauricio Hadida (the Chilean Maritime Governor), Javier Icka Acuña, Felipe Morales Guajardo and Caleb, who provided and discussed the footage analyzed here, and Mauricio Molina and Sebastián Correa for their aid in generating the wave dataset. We also thank Patricio Catalán, Rodrigo Cienfuegos and Kwok Fai Cheung for fruitful discussions in initial phases of this study, and Roberto Carvajal for connecting us with the local Maritime Authority and for showing us the video that motivated this study. The atmospheric data were provided by the “Dirección Meteorológica de Chile” (http://www.meteochile.gob.cl). The sea-level data were provided by the “Servicio Hidrográfico y Oceanográfico de la Armada de Chile” (http://www.shoa.cl) through the Intergovernmental Oceanographic Commission's sea level station monitoring facility (http://www.ioc-sealevelmonitoring.org/). Wind fields for wave modeling are from NOAA’s Global Forecast System GFS database https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-forcast-system-gfs. We sincerely thank three anonymous reviewers and Alexander Rabinovich (Guest editor), who, besides providing valuable comments and suggestions to improve our paper, encouraged us to tell the story in a much focused way. PW thanks grant ANID FONDAP 15110017 (CIGIDEN) for the financial support during this study. Funding came from the Iniciativa Científica Milenio (ICM) through Grant Number NC160025 “Millennium Nucleus CYCLO: The Seismic Cycle Along Subduction Zones.” and by Chile’s Fondo Nacional de Desarrollo Científico y Tecnológico, FONDECYT Projects N°1190258 and N°1181479.
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Iniciativa Científica Milenio (ICM) through Grant Number NC160025 “Millennium Nucleus CYCLO: The Seismic Cycle Along Subduction Zones.”
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Carvajal, M., Winckler, P., Garreaud, R. et al. Extreme sea levels at Rapa Nui (Easter Island) during intense atmospheric rivers. Nat Hazards 106, 1619–1637 (2021). https://doi.org/10.1007/s11069-020-04462-2
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DOI: https://doi.org/10.1007/s11069-020-04462-2