Future Changes in Built Environment Risk to Coastal Flooding, Permanent Inundation and Coastal Erosion Hazards

Abstract

Sea-level rise will cause erosion of land, deeper and increasingly frequent flooding and will eventually permanently inundate low-elevation land, forcing the adaptation of seaside communities to avoid or reduce risk. To inform adaptation planning, we quantified the effects of incremental relative sea-level rise (RSLR) on exposed land area, number and replacement value of buildings within Tauranga Harbour, New Zealand. The assessment compared three coastal hazards: flooding, permanent inundation and erosion. Increasingly frequent coastal flooding will be the dominant trigger for adaptation in Tauranga. In the absence of adaptation, coastal flooding, recurring at least once every 5 years on average, will overtake erosion as the dominant coastal hazard after about 0.15–0.2 m RSLR, which is likely to occur between the years 2038–2062 in New Zealand and will rapidly escalate in frequency and consequence thereafter. Coastal erosion will remain the dominant hazard for the relatively-few properties on high-elevation coastal cliffs. It will take 0.8 m more RSLR for permanent inundation to reach similar impact thresholds to coastal flooding, in terms of the number and value of buildings exposed. For buildings currently within the mapped 1% annual exceedance probability (AEP) zone, the flooding frequency will transition to 20% AEP within 2–3 decades depending on the RSLR rate, requiring prior adaptive action. We also compared the performance of simple static-planar versus complex dynamic models for assessing coastal flooding exposure. Use of the static-planar model could result in sea level thresholds being reached 15–45 years earlier than planned for in this case. This is compelling evidence to use dynamic models to support adaptation planning.

The Global Drivers of Chronic Coastal Flood Hazards Under Sea‐Level Rise

“…It is therefore unclear a priori whether it is more extreme and unprecedented episodic flooding (e.g., Kirezci et al., 2020) or more frequent occurrences of present‐day minor, moderate and major floods (this study) that will trigger adaptive actions to be taken (Stephens et al., 2018). Recent studies have sought to answer this question for specific coastal communities (Buchanan et al., 2019; Ghanbari et al., 2020; Stephens et al., 2021), but no similar studies have occurred over regional or national domains. This study has identified that when floods become frequent, they are driven by different physical processes than episodic flooding.…”

High-frequency sea-level extremes: Global correlations to synoptic atmospheric patterns

“…The latter study revealed that, in some climate scenarios, meteotsunami intensity may increase substantially (for about 30% till 2 100 in the RCP 8.5 greenhouse gas emission scenario). With all of this taken into a planning, the last component of the sea level budget, still not taken in coastal hazard assessment studies (Stephens et al, 2021), may be finally used in coastal planning and risk estimates at high resolution.…”

Price recovery after the flood: risk to residential property values from climate change‐related flooding*

“…There have been some general assessments of New Zealand asset exposure and risk from coastal inundation due to sea level rise (e.g. PCE 2015; Paulik et al 2019;Paulik et al 2021;Stephens et al 2021). To date, research on the financial impacts of climate-change related flood hazards [CCRFH] in New Zealand has focused on insurability (Storey et al 2017), historical insurance losses (Fleming et al 2018;Frame et al 2018), the burden of responsibility (Ellis 2018) and impacts on local government infrastructure (Simonson and Hall 2019).…”

“…2021; Stephens et al . 2021). To date, research on the financial impacts of climate‐change related flood hazards [CCRFH] in New Zealand has focused on insurability (Storey et al .…”