Waves
Extreme waves are a hazard both at the coast and at sea. Waves from winter storms cause large impacts around our coastline, with potential for coastal erosion, flooding, and overtopping of sea-defences in extreme conditions. The largest waves in UK waters are found on the Atlantic (west-facing) coasts where waves can propagate over large fetches from the ocean. Many factors affect the height of waves in UK waters, but for the Atlantic margin the persistence and strength of westerly winds are particularly important.
There is much interest in whether we can detect a change in wave climate. Rather dramatic increases in wave height occurred between 1960 and 1990, but these are now seen as just one feature within a longer history of variability. There is no clear pattern in results since 1990. Natural variability in wave climate is strong and the role of anthropogenic forcing is uncertain. Although there have been many suggestions of increased winter storminess both in the climate change literature and the media, any significant changes have been contradicted in the most recent climate projections for the UK. Some projections of climate predict a southward change in the location of the winter storm track (the jetstream), which could result in lower wave heights to the north of the UK and slightly greater wave heights in some southern regions. There is however no consensus on the future storm or wave climate, or storm track.
(Extracted from Woolf, D., and J. Wolf (2010) Storms and Waves in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 15pp. www.mccip.org.uk/arc)
The largest waves occur in deep water, away from the coast. Exceptional wave heights were recorded in the northern Rockall Trough during a UK research cruise in February 2000. Individual wave heights of up to 29.1 m and significant wave heights of 18.5m were observed by a ship-borne wave recorder on RRS Discovery. The measured significant wave height exceeded any previously recorded values, including those observed under hurricanes in the tropical North Atlantic. During a 12-hour period on 8-9 February, a total of 23 waves exceeded 20 m peak-to-trough height (Figure 1). The extreme waves were generated by a long fetch and resonant conditions, during which the wave group travelled at the same speed as the high wind feature across the North Atlantic.
