A simple technique for estimating an allowance for uncertain sea-level rise
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Projections of climate change are inherently uncertain, leading to considerable debate over suitable allowances for future changes such as sea-level rise (an ‘allowance’ is, in this context, the amount by which something, such as the height of coastal infrastructure, needs to be altered to cope with climate change). Words such as ‘plausible’ and ‘high-end’ abound, with little objective or statistically valid support. It is firstly shown that, in cases in which extreme events are modified by an uncertain change in the average (e.g. flooding caused by a rise in mean sea level), it is preferable to base future allowances on estimates of the expected frequency of exceedances rather than on the probability of at least one exceedance. A simple method of determining a future sea-level rise allowance is then derived, based on the projected rise in mean sea level and its uncertainty, and on the variability of present tides and storm surges (‘storm tides’). The method preserves the expected frequency of flooding events under a given projection of sea-level rise. It is assumed that the statistics of storm tides relative to mean sea level are unchanged. The method is demonstrated using the GESLA (Global Extreme Sea-Level Analysis) data set of roughly hourly sea levels, covering 198 sites over much of the globe. Two possible projections of sea-level rise are assumed for the 21st century: one based on the Third and Fourth Assessment Reports of the Intergovernmental Panel on Climate Change and a larger one based on research since the Fourth Assessment Report.
KeywordsScale Parameter Exceedance Probability Uncertainty Distribution Gumbel Distribution Glacial Isostatic Adjustment
This paper was supported by the Australian Government’s Cooperative Research Centres Programme through the Antarctic Climate & Ecosystems Cooperative Research Centre. Sea-level data were supplied by European Sea-Level Service, Global Sea Level Observing System (GLOSS) Delayed Mode Centre, Helpdesk Water (Netherlands), Instituto Español de Oceanographia (Spain), Istituto Talassografico di Trieste (Italy), Marine Environmental Data Service (Canada), National Oceanography Centre Liverpool (UK), National Tidal Centre (Bureau of Meteorology, Australia), Norwegian Mapping Authority, Service Hydroographique et Océanographique de la Marine (France), Swedish Meteorological and Hydrological Institute and University of Hawaii Sea Level Centre (USA).
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