Sea‐level scenarios for evaluating coastal impacts

Abstract

Global-mean sea-level rise will drive impacts and adaptation needs around the world's coasts over the 21st century and beyond. A key element in assessing these issues is the development of scenarios (or plausible futures) of local relative sea-level rise to support impact assessment and adaptation planning. This requires combining a number of different but uncertain components of sea level which can be linked to climatic and non-climatic (i.e., uplift/subsidence of coastal land) factors. A major concern remains about the possibility of significant contributions from the major Greenland and Antarctic ice sheets and this must be factored into the assessments, despite the uncertainty. This paper reviews the different mechanisms which contribute to sea-level change and considers a methodology for combining the available data to create relative (or local) sea-level rise scenarios suitable for impact and adaptation assessments across a range of sophistication of analysis. The methods that are developed are pragmatic and consider the different needs of impact assessment, adaptation planning, and long-term decision making. This includes the requirements of strategic decision makers who rightly focus on low probability but high consequence changes and their consequences. Hence plausible high end sea-level rise scenarios beyond the conventional Intergovernmental Panel on Climate Change (IPCC) range and which take into account evidence beyond that from the current generation of climate models are developed and their application discussed. Continued review and development of sea-level scenarios is recommended, starting with assimilating the insights of the forthcoming IPCC AR5 assessment.

Sea Level Change and Coastal Climate Services: The Way Forward

“…Global to national level users, for example, require assessments of impacts over varying spatio-temporal scales, in order to stimulate the implementation of adaptation plans or regulations, as in the French example (Row 3a in Table 2). Other users at regional to local scales require services to support preparedness to current sea level and flood hazards (Row 3b in Table 2) and to understand local to regional adaptation needs over multi-decadal timescales [78], including critical infrastructure where relevant [11] (Row 3c in Table 2). The U.S. example shows that coastal researchers and engineers have already partly responded to these needs, for example by providing annual predictions of high-water event frequencies to help budget appropriately in terms of costs of preparedness and crisis management (e.g., road closures, installation of pumps, sandbags, inflow preventers in storm water systems).…”

“…In the remainder of this section, we thus examine current interactions and information flows among stakeholders of coastal climate services (arrows in Figure 2), in order to identify specific barriers to their further development. Specifically, we successively examine three important barriers in the development phase (see Table 3 Insufficient awareness regarding vulnerability to climate change [4] Partial (see Section 2): sea level projections beyond the likely range of IPCC are frequently used [7,78,100], but most users are unaware about long term SLR commitment.…”

A review of potential physical impacts on harbours in the Mediterranean Sea under climate change

“…-Projections of SLR in the Mediterranean area: Lionello (2013), Scarascia and, Nicholls et al (2014) and Lionello et al (2015).…”

“…differences between scenarios are not seen until after mid-century. Higher rises are considered possible (up to 2m per century), although with a lower probability (Nicholls et al 2014). …”

“…Dynamic oceanography associated with episodic events may introduce several centimetres (up to more than 5 cm in the Mediterranean) of mean sea level variation (Adloff et al 2015) although there is no predicted seasonal bias in the obtained sea level rise, indicating that the seasonal cycles will remain unaffected. The resulting relative (sea referred to land) levels also reflect more local anthropogenic impacts that can add a few millimetres to centimetres per year (Nicholls et al 2014). This combination of factors must be considered for the assessment of harbour operability, where also the local settling of heavy infrastructure (e.g.…”