# Marine & coastal projections images Figures 4.3-4.6: surges

Figures 4.3-4.6 show the PPE ensemble mean trend in return level for four different return periods (2, 10, 20-and 50 yr) for locations around the UK mainland coast.*

The figures also show a measure of the uncertainty in the PPE ensemble mean trends and a measure of the probabilities of such trends occurring due to variability (rather than climate change). As may be expected, the statistical significance generally decreases as we move to longer return periods and the uncertainties increase. The probabilities of the increases being due to variability (shown in the right-hand panels) are based on the assumption of a normal distribution of the ratio of trend to uncertainty. Whilst the extremes themselves follow a different (extreme value) distribution, this assumption is not unreasonable for the trends. The probabilities are assessed on a point-by-point basis, without regard to any spatial coherence.

* Negative trends are included in the grey shading of each plot, since their magnitude is of little interest. However, for completeness, we remark that in each case the absolute value of the most negative trend is comparable to the largest positive trend.

**Figure 4.4**: PPE ensemble mean trends in skew surge 10 yr return level from the storminess component only. Negative trends are included in the grey shading.

**Figure 4.5**: PPE ensemble mean trends in 20 yr skew surge return level from the storminess component only. Negative trends are included in the grey shading.

**Figure 4.6**: PPE ensemble mean trends in 50 yr skew surge return level from the storminess component only. Negative trends are included in the grey shading.

- Last updated: Tuesday, 11 November 2014