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How the waves off the west coast may change in the future?
12 November 2015

Global climate models predict the increased warming of the earth's atmosphere and oceans. Climate change will affect mean sea-levels, the frequency and severity of extreme weather events, winds and ocean waves. Because Ireland's marine resource is so important, it is necessary to quantify the potential impact global climate change might have.  These changes then need to be carefully assessed for long-term marine and coastal planning. The primary goal of our study is to examine what kind of changes in the wave climate Ireland can expect in the future (at the end of the 21st century) and contrast them to the present wave climate.

Figure 1: Left panel: The three wave model grids used in the computer simulation of the future wave climate of Ireland, including the North Atlantic basin. Right panel: a zoomed in image of the wave model grid around Ireland (shown in magenta in the left panel).

Met Éireann researchers have examined future wave climate projections for Ireland using the WAVEWATCH III wave model (a numerical computer simulation) to model the ocean waves around Ireland. Global atmosphere-ocean-sea-ice climate model EC-Earth winds were used to drive a basin scale wave model (of the North Atlantic) in order to capture distant swells. These were then used to force two higher resolution nested grids zooming in on Ireland (see Figure 2). Looking at Figure 2, the resolution, or distance between each grid point, decreases (gets smaller) as the computer simulation calculates the waves around Irish shores. The finest horizontal resolution is 1 km in the near-shore. This is because we want the most accurate results to be modelled for the area of interest: Ireland. It is not possible to have the same high resolution over the entire North Atlantic basin, as it would require too much computing power.

The wave model projections show that for the Representative Concentration Pathway (RCP) 8.5 an overall decrease (up to 10-15%) in the average and extreme (the highest 5% of waves) for annual, Boreal winter and summer significant wave heights around Ireland. So the wave climate model projections predict a small overall reduction in the mean wave heights that will reach Ireland's shores towards the end of the 21st century. However, don't hang up your surf boards just yet, there will still be plenty of big waves to go around!

Figure 2: Projected future changes in significant wave height (m) to the end of the 21st century. Left panel: The modelled annual (a), winter (c) and summer (e) means of significant wave height from 1980-2009. Right panel: The projected changes in significant wave height for 2070 to 2099 under the RCP8.5 scenario.

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