5 Climate driven changes in waves

In this chapter we examine the projections of future wave climate around the UK driven by winds from a subset of the Met Office climate model ensemble members. The wave model which is used is based on the well-tested third-generation spectral model WAM implemented on two grids: a coarse 1° grid for the whole and a 12 km model of the NW European continental shelf. The models were run using three sets of atmospheric model wind forcing from low, mid and high climate senstivity variants of the Met Office perturbed physics ensemble (PPE). All results are for the medium emissions scenario.

Key Findings

• The wave model has been well-validated previously and here it is shown to be in reasonable agreement with the ERA-40 reanalysis (which is a comprehensive global hind-cast of the last 40 yr of waves and wind, combining model fields with a wide range of observations) for the present-day wave climate for the NE Atlantic.

• Seasonal mean and extreme waves are generally expected to increase slightly to the SW of the UK, reduce to the north of the UK and experience little change in the North Sea. There are large uncertainties especially with the projected extreme values.

• Changes in the winter mean wave height are projected to be between –35 cm and + 5 cm. Changes in the annual maxima are projected to be between –1.5 m and +1 m. Projections of longer return period wave heights will reflect the same pattern but with larger error bars.

• Here we present a first look at the range of uncertainty. Only three ensembles were used (out of 11) so the spread is clearly a minimum estimate. The simulation corresponding to low climate sensitivity shows larger increases of wave height but the latitudinal pattern remains similar in each case.

• One wave model simulation was carried out for the whole 140 yr to examine natural variability. The large inter-annual variability in wave parameters, especially extreme values, shows that looking at differences between two 30-yr time slices is of limited value in determining trends. Statistically significant trends in annual maximum wave height of –0.3 cm/yr are identified to the north of Scotland.

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