Wave climate trends and breakpoints during the Atlantic Multidecadal Oscillation (AMO) in southern Brazil

Abstract

Understanding how wave climate variability and its trends change over time are crucial analyses required to mitigate potential wave-induced impacts and adapt coastal areas to such effects. The long-term trends and breakpoints of the wave energy flux (WEF) and its relationship with teleconnection patterns in southern Brazil were studied using ERA-5 wave reanalysis with validation using a waverider. We determined that the interannual mean WEF (WEFm) and extreme WEF (WEF98) that reaches the southern Brazil have increased over the past four decades, with a increment of 0.063 and 0.17 kW/m/year, respectively 0.63 and 0.29% per year. By the Muggeo method we determined that subperiods with increasing WEFm trends are related to the SSE and SSW quadrants and that these are also the most energetic ones and with the highest annual increment rates of WEFm and WEF98. Our results also suggest that the positive trends observed in interannual WEF values are likely related to the long term transition of cold to warm Atlantic Multidecadal Oscillation (AMO) phase in the western South Atlantic Ocean. From a coastal risk perspective, it is important to understand the relationship between climatic indices and the wave climate to support long-term coastal management policies.

Long-term trends and wave climate variability in the South Atlantic Ocean: The influence of climate indices

“…Global wave models thus provide a useful alternative to address the space and time variability and trends of wave conditions in the SH (Hemer et al, 2010). We used the 3-hourly 72-years global wave hindcast produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) -ERA 5 (see Hersbach et al, 2020) from 1950 to 2021, from which significant wave height (Hs), peak wave period (Tp) and direction (θ) were extracted, from which the wave energy flux WEF was also computed (Antolínez et al, 2016;Mentaschi et al, 2017;Marshall et al, 2018;Reguero et al, 2019;Odériz et al, 2020a;Odériz et al, 2020b;Maia et al, 2022) through the equation:…”

“…Outputs were extracted on a regular grid with 0.5° resolution covering the southern Atlantic Ocean between 5°N-60°S and 69.5°W-20°E, thus a total of 23,580 individual grid points. ERA5 validation for the South Atlantic Ocean is given in Odériz et al, 2020a, Odériz et al, 2020b, Maia et al, 2022and Cotrim et al, 2022 showing a generally good performance in replicating wave high inter-annual variability compared to altimetry and buoy measurements. Three virtual wave buoys were used to address the spatial distribution of wave heights in deep waters along the South Atlantic Ocean: Nt: North; Ct: Central; St: South (Figure 1).…”

“…The wave climate therefore deeply affects where and how coastal and offshore infrastructures such as harbors and wave power generation plants can be built (Reguero et al, 2013(Reguero et al, , 2019. It is thus critical to understand the ocean wave climate variability and trends (Barnard et al, 2015;Mentaschi et al, 2017;Marshall et al, 2018;Reguero et al, 2019;De Leo et al, 2021;Maia et al, 2022). In addition, according to Morim et al (2019), approximately 50% of the world's coastline is at risk from wave climate change, with ~40% revealing robust changes in wave properties.…”

“…Large-scale patterns of atmospheric and/or oceanic variability are often addressed though climate indices such as the Southern Annular Mode (SAM) (also referred to as the high-latitude mode and the Antarctic Oscillation (AAO)), Tropical Southern Atlantic Index (TSA), Tropical Northern Atlantic Index (TNA), Western Hemisphere Warm Pool (WHWP) and the Atlantic Multidecadal Oscillation (AMO) (Thompson and Wallace 2000;Kerr 2000;Trenberth et al, 2002;Hemer et al, 2010;Reguero et al, 2013). Given that these patterns mostly superimpose and that waves are generated from different locations, the wave climate variability at a given location is modulated by the combination of several climate indices and teleconnections patterns Reguero et al, 2019;Silva et al, 2020;Maia et al, 2022), and a given mode of variability can affect multiple ocean basins and hemispheres (Oliveira et al, 2019). According to Silva et al (2020), in the recent decades the predominant wind-wave climate has been shifting in both direction and magnitude in both the Northern and Southern Hemispheres (Reguero et al, 2019), a phenomenon likely in response to altered atmospheric dynamics and interhemispheric teleconnections in association with increasing global temperature (Morim et al, 2019;Meucci et al, 2020;O'Grady et al, 2021).…”

“…According to Wang et al (2008) and Kayano et al (2019), the hurricanes and cyclones behaviors in the Atlantic Ocean are modulated by AMO oscillations, respectivly. Reguero et al (2019) and Maia et al (2022) identified strong correlations between the wave energy flux (WEF) and AMO behavior in the Southern Ocean and western South Atlantic Ocean, respectively. Another relevant climate index with important influence in the Atlantic Ocean is the TSA pattern which is associated with wave height increase in the northern equatorial Atlantic border of the continent and in the Rio dela Plata area, whereas the WEF affects wave directionality (Reguero et al, 2013).…”