Coastal Wave Extremes around the Pacific and Their Remote Seasonal Connection to Climate Modes

Abstract

At first order, wind-generated ocean surface waves represent the dominant forcing of open-coast morpho-dynamics and associated vulnerability over a wide range of time scales. It is therefore paramount to improve our understanding of the regional coastal wave variability, particularly the occurrence of extremes, and to evaluate how they are connected to large-scale atmospheric regimes. Here, we propose a new “2-ways wave tracking algorithm” to evaluate and quantify the open-ocean origins and associated atmospheric forcing patterns of coastal wave extremes all around the Pacific basin for the 1979–2020 period. Interestingly, the results showed that while extreme coastal events tend to originate mostly from their closest wind-forcing regime, the combined influence from all other remote atmospheric drivers is similar (55% local vs. 45% remote) with, in particular, ~22% coming from waves generated remotely in the opposite hemisphere. We found a strong interconnection between the tropical and extratropical regions with around 30% of coastal extremes in the tropics originating at higher latitudes and vice-versa. This occurs mostly in the boreal summer through the increased seasonal activity of the southern jet-stream and the northern tropical cyclone basins. At interannual timescales, we evidenced alternatingly increased coastal wave extremes between the western and eastern Pacific that emerge from the distinct seasonal influence of ENSO in the Northern and SAM in the Southern Hemisphere on their respective paired wind-wave regimes. Together these results pave the way for a better understanding of the climate connection to wave extremes, which represents the preliminary step toward better regional projections and forecasts of coastal waves.

A Multidecadal Assessment of Mean and Extreme Wave Climate Observed at Buoys off the U.S. East, Gulf, and West Coasts

“…The wave climate in the Northern Hemisphere is also influenced by waves generated in the Southern Hemisphere, especially during austral winters. This is illustrated by the correlation between the SAM index and the wave energy at a region from the Eastern South Pacific to mid-latitude regions of the Eastern North Pacific [57]. Thus, the variability in the SAM, which is associated with the north-south movement of the westerly wind belt surrounding Antarctica, could influence the calculated trends in the SWH.…”

“…In the Eastern North Pacific Ocean, the wave climate is correlated with the El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM) [21,56,57]. During El Niño events (+0.5 • C SST anomaly in the NINO3.4 region), the northern jet stream intensifies and shifts southward, resulting in an equatorward shift in the storm tracks of the North Pacific [58].…”

Seasonal forecasts of the world’s coastal waterline: what to expect from the coming El Niño?

“…Because 600 million people live in coastal areas less than 10 meters above sea level, the links between ENSO and coastal vulnerability have been studied extensively [20][21][22][23][24][25][26][27][28][29][30] . In particular, a recent study has built on the many theoretical breakthroughs in understanding the complex and diverse regimes of ENSO and their teleconnections 31 , including their remote effects on drivers of coastal variability (e.g., waves, sea level, and rivers) [32][33][34] , to formulate a climate-based conceptual model of global coastal waterline evolution 35 taking advantage of a new data resource allowing to assess multi-year fluctuations in its position.…”

A Systematic Review of Oceanic-Atmospheric Variations and Coastal Erosion in Continental Latin America: Historical Trends, Future Projections, and Management Challenges

“…ENSO phases influence wave systems along the Eastern Pacific coasts, with wave power increasing during El Niño in some areas and decreasing in others [24,36]. In winter, El Niño impacts the tropical northeast, reducing trade winds and intensifying wave activity, while in summer it affects the tropical northwest, increasing tropical cyclone activity and extreme waves [35,37]. Tropical Atlantic temperature, linked to ENSO, affects La Niña conditions in the North Tropical Atlantic, altering trade winds and storm intensity [10,34,38,39].…”

“…In addition to ENSO, the Southern Annular Mode (SAM) is another significant driver of climate variability affecting various Latin American coasts. SAM influences temperature and precipitation in southern South America, correlating with sea surface warming in tropical latitudes, and heightened wave events in the southern Pacific at low latitudes [34,37,41]. A trend toward the positive SAM phase, possibly due to anthropogenic influence and climate change, has been observed in recent decades [27,45].…”