Information for Australian impact and adaptation planning in response to sea-level rise

Abstract

Sea levels along Australia's coastline are influenced by natural climate variability and anthropogenic climate change. Projections of sea-level rise (SLR) for 2090 for the Australian coastline are similar to the global mean sea-level projections. The global and regional projections are almost independent of the Representative Concentration Pathways (RCPs) for greenhouse gas emissions chosen for the first decades of the 21 st century, but they begin to diverge significantly from about 2050. For the business-as-usual scenario (RCP8.5), the rates increase steadily through the 21 st century, reaching almost 12 mm yr -1 by 2100 at all locations. For the intermediate scenarios of RCP 6.0 and RCP 4.5, the rates stabilise in about 2090 and 2060 at about 7-8 and 6 mm yr -1 , respectively. For the strong mitigation scenario (RCP 2.6, requiring significant and urgent mitigation of greenhouse gas emissions), the rate of rise stabilises much earlier than the other scenarios and then reduces slightly to about 4 mm yr -1 . On the north and west coasts of Australia, the observed sea-level trends from the start of the projections in 1996 to 2010 are larger than the model projections as a result of the combined effect of SLR and internal modes of climate variability.The impacts of SLR will be felt most profoundly during extreme sea-level events. The meteorological and climate processes that contribute to extreme sea levels around the coast of Australia are highly regionally heterogeneous. Allowances were calculated that provide estimates of the height that present assets or their protective measures would need to be raised to ensure that the likelihood of exceedance of those levels in the future does not change from the present climate. These allowances vary according to SLR projections, their uncertainties and the variability of extreme sea levels. For 2030, when the uncertainty surrounding future SLR scenarios is small, the allowances are approximately the median projected SLR. However by 2090, the larger uncertainties associated with the projections lead to allowances that typically lie towards the upper end of the range of projected SLR. IntroductionSea-level rise (SLR) is a significant concern for Australia with about half the population living within 7 km of the coast (Chen and McAneney, 2006) and a significant amount of industry and infrastructure located in the coastal zone. Between 22 and 35% of residential dwellings in Australia have been identified as potentially exposed to flooding under a SLR scenario of 1.1 metres (Department of Climate Change, 2009 Coastal infrastructure and coastal ecosystems are most at risk during extreme sea-level events, caused by storm surges and other contributing factors such as astronomical tides. It is therefore of vital importance that credible and robust up-to-date information on SLR projections and the impacts on extreme events are available for coastal planning and adaptation.The Intergovernmental Panel for Climate Change (IPCC) assessments are a major source of SLR information, with ...

Sea Level Change and Coastal Climate Services: The Way Forward

“…While flexible probabilistic modelling approaches for estimating setback lines from erosion are increasingly being developed [106,116,132,133], care is required in interpreting the uncertainties reported in IPCC SLR scenarios, particularly when representing the uncertainties by probability distributions (see Section 3.4.3 below). Similar cautions apply to the calculation of sea level allowances [32,[90][91][92]. Furthermore, in many areas where active sediment processes are taking place, changing bathymetries modify coastal hydrodynamic processes and the related flooding hazards [55,134].…”

“…For example, the state of Victoria has stipulated since 2008 (and reassessed in 2014) that planning authorities must plan for a SLR increase of 'not less than' 0.8 m by 2100, whereas in South Australia new developments should take into consideration 0.3 m SLR by 2050 and a further 0.7 m SLR between 2050 and 2100 [58]. To support local council planning and management, CCS in the form of regional sea level projections and their uncertainties up to 2100, including sea level allowances to support coastal defense upgrades, have been developed [32]. These are delivered as a national climate service along with other projected atmospheric and oceanic variables such as temperature, precipitation, wind, ocean and pH [59], but also as a more specific coastal climate service at the scale of individual Australian coastal councils on the 'CoastAdapt' web site [60].…”

“…Lack of understanding of the decision-making context [3] Partial (see Section 2): for example, sea level projections have been used in coastal engineering design at the municipality scale in Australia [32,106] Differences in working times for scientists and decision makers providing or using climate services [4] Yes: the French example shows that by establishing a regulation in favour of adaptation, coastal stakeholders require operational products within six months or a year (e.g., multidecadal shoreline erosion predictions), while research has hardly provided with a satisfactory level of confidence so far in this area (Section 3.1). Lack of formalized requirements from translators of climate information into services [101,103] Partial: coastal service providers have hardly provided detailed formalized requirements for sea level information besides Nicholls et al [78]; see Section 3.3)…”

“…For example, coastal impacts studies are commonly used to justify "low-regret" strategies, such as maintaining ecological services and quality in coastal zones [115], relocating some buildings or activities, or to limit further urbanization in low lying or erodible coastal areas [116]. They are also used to anticipate the upgrade of defence works in coastal areas, which will be necessary to control safety levels despite sea level rise, demographic growth and land use pressure [32,36,89,90]. Moreover, other products are emerging: for example, coastal engineers not only design coastal defences that anticipate future upgrades [117], but also perform vulnerability assessments for existing infrastructure, which may have already experienced changing sea levels over a century or more [100].…”

Projected 21st Century Sea-Level Changes, Observed Sea Level Extremes, and Sea Level Allowances for Norway

“…Allowances are calculated in two alternative ways using a normal distribution: (1) assuming that the model spread does in fact correspond to the 5% and 95% probability bounds (e.g., [62,63]) and (2) assuming that the model spread being defined as the likely range in IPCC AR5 (p > 66%) corresponds to the 17% and 83% probability bounds. Note that the latter is one interpretation of the likely range.…”