• Energy Research

Coastal hazards result from erosion of the shore, or flooding of low-elevation land when storm surges combine with high tides and/or large waves. Future sea-level rise will greatly increase the frequency and depth of coastal flooding and will exacerbate erosion and raise groundwater levels, forcing vulnerable communities to adapt. Communities, local councils and infrastructure operators will need to decide when and how to adapt. The process of decision making using adaptive pathways approaches, is now being applied internationally to plan for adaptation over time by anticipating tipping points in the future when planning objectives are no longer being met. This process requires risk and uncertainty considerations to be transparent in the scenarios used in adaptive planning. We outline a framework for uncertainty identification and management within coastal hazard assessments. The framework provides a logical flow from the land use situation, to the related level of uncertainty as determined by the situation, to which hazard scenarios to model, to the complexity level of hazard modeling required, and to the possible decision type. Traditionally, coastal flood hazard maps show inundated areas only. We present enhanced maps of flooding depth and frequency which clearly show the degree of hazard exposure, where that exposure occurs, and how the exposure changes with sea-level rise, to better inform adaptive planning processes. The new uncertainty framework and mapping techniques can better inform identification of trigger points for adaptation pathways planning and their expected time range, compared to traditional coastal flooding hazard assessments.

Decision makers face challenges in coastal areas about how to address the effects of ongoing and uncertain sea-level rise. Dynamic adaptive pathways planning (DAPP) and Real Options Analysis (ROA) can support decision makers to address irreducible uncertainties in coastal areas. This paper sets out what we learned by complementing multi-criteria decision analysis with DAPP and ROA when developing a 100-year coastal adaptation strategy in Hawke's Bay, New Zealand. Lessons include the value of collaborative community and decision maker processes for increasing understanding about the changing risk over time, and the need to take early actions that enable a shift in pathway before those actions become ineffective. Modifications to the methods highlighted the importance of using several plausible scenarios for stress-testing options; considering costs and consent-ability early, to avoid the perception that hard protection will last; which criteria are appropriate for communities to assess; and making many pathways visible for future decision makers. We learned about the difficulties shifting thinking from short-term protection actions to longer-term anticipatory strategies. We found that a pathways system will require ongoing political leadership and governance with monitoring systems that can manage the adaptive process over long timeframes, by governments and their constituent communities.

Coastal flooding from extreme sea levels will increase in frequency and magnitude as global climate change forces sea-level rise (SLR). Extreme sea-level events, rare in the recent past (i.e., once per century), are projected to occur at least once per year by 2050 along many of the world’s coastlines. Information showing where and how built-environment exposure increases with SLR, enables timely adaptation before damaging thresholds are reached. This study presents a first national-scale assessment of New Zealand’s built-environment exposure to future coastal flooding. We use an analytical risk model framework, “RiskScape”, to enumerate land, buildings and infrastructure exposed to a present and future 100-year extreme sea-level flood event (ESL100). We used high-resolution topographic data to assess incremental exposure to 0.1 m SLR increases. This approach detects variable rates in the potential magnitude and timing of future flood exposure in response to SLR over decadal scales. National built-land and asset exposure to ESL100 flooding doubles with less than 1 m SLR, indicating low-lying areas are likely to experience rapid exposure increases from modest increases in SLR expected within the next few decades. This highlights an urgent need for national and regional actions to anticipate and adaptively plan to reduce future socio-economic impacts arising from flood exposure to extreme sea-levels and SLR.