Waves and climate change in the Sea of the Hebrides

There is mounting evidence for the effects of climate change both globally and regionally. Global warming and sea level rise are now established but may appear insignificant locally, although the expected acceleration in rate may make this more noticeable. The most important issue for individuals and communities, who have to make decisions (based on existing evidence) about how to manage response to climate change, is the likely local impact. This may be in terms of secondary effects, e.g changes in rainfall, and may vary greatly from the global average. Wave height in the North Atlantic, as observed from in-situ and altimeter observations, has increased over the last quarter-century. The North Atlantic Oscillation (NAO) appears to be correlated with increasing wave height in the North Atlantic over recent decades. Prediction of future impacts requires understanding the role of such decadal oscillations and their likely future evolution as well as long-term trends in sea level and wave height due to global warming and possible rapid climate change scenarios. It is important to understand these effects on relatively small scales. Here we examine the impacts of changing wave climate on the rocky coast of NW Scotland, specifically the Sea of the Hebrides.

The Sea of the Hebrides is the body of water that lies between the Outer and Inner Hebrides island groups in NW Scotland. The impact of any increase in wave height in the North Atlantic at the coastline will be most significant in this area Crofting, fishing, fish fanning and tourism are the most significant economic activities. Impacts of climate change in this area may include interference to ferries and fishing activity, changes in potential wave energy availability and changes in coastal erosion and habitats.

Wave models provide a tool to study detailed impacts of various climate change scenarios. The model system used here comprises three nested models using both the PRO-WAM and SWAN models, from a V North Atlantic model, through a 7.5km Malin/Hebrides Shelf model to a 1.85km Sea of Hebrides model. This allows the effect of winds over the whole North Atlantic to be investigated while also studying the local coastal wave impact including refraction and shoaling around the Western Isles of Scotland and make the connection between the statistical results from altimeter data to the dynamics.