Two uncertainty distributions were used (normal and raised-cosine); Fig. 2 and Fig. 4, and Appendix B, show the results for a normal distribution which has fatter tails and which yields a slightly higher allowance. Planning allowances have typically been selected by choosing a specific percentile of a projection of future global-average sea-level rise. Often the 95-percentile upper limit, which is the one provided by the IPCC AR4 (Meehl et al., 2007), has been chosen. However, PD-166866 datasheet as shown in Fig. 3 (for the period 1990–2100), if sea-level rise were globally uniform, an allowance equal to the 95-percentile limit is generally significantly

larger than would be required STA-9090 supplier to preserve the frequency of flooding events under sea-level rise; for the period 1990–2100, only 2.6% of the locations considered have allowances greater than the 95-percentile upper limit. The spread of allowances in Fig. 3 is entirely due to spatial variations in the statistics of storm tides (specifically, the Gumbel scale parameter). When the spatial variation of projected sea-level rise (due to ongoing changes in the Earth’s loading and gravitational field,

thermal expansion, ocean dynamics and GIA) is included, the distribution of the allowances widens significantly (Fig. 5, for the period 1990–2100). This widening is related to locations (in northern regions of North America and Europe) which experience strongly negative GIA, and others (in the northwest region of North America) which are influenced by present changes in glaciers and icecaps. These processes contribute a significant fall in sea level, leading to negative

‘allowances’, some of which are less than −1 m. The spread of allowances covers the entire 90-percentile range of the A1FI projections of global-average sea-level rise, with 9% of the locations having allowances less than the 5-percentile lower limit and 29% of the locations having allowances greater than the 95-percentile upper limit. Fig. 4 shows the global distribution of the allowances for the period 1990–2100. Obvious features are the low and negative allowances during in the northern regions of North America and Europe (where the land is rising due to GIA and to present changes in glaciers and icecaps), and higher allowances along the eastern coastline of North America (where the land is sinking, again due to GIA). Appendix B provides a table of allowances for the periods 1990–2100 and 2010–2100. These may be used as a starting point for the determination of allowances for planning and policy decisions. However, the following caveats should be recognised: 1. The determination of allowances given in this paper is based on the assumption that the Gumbel scale parameter (and hence the variability of the storm tides) will not change in time.