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Scott Stephens
National Institute of Water and Atmospheric Research, P.O. Box 11 115, Hamilton 3251, New Zealand

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Journal article
Published: 24 March 2020 in Natural Hazards and Earth System Sciences
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Coastal flooding is a major global hazard, yet few studies have examined the spatial and temporal characteristics of extreme sea level and associated coastal flooding. Here we analyse sea-level records around the coast of New Zealand (NZ) to quantify extreme storm-tide and skew-surge frequency and magnitude. We identify the relative magnitude of sea-level components contributing to 85 extreme sea level and 135 extreme skew-surge events recorded in NZ since 1900. We then examine the spatial and temporal clustering of these extreme storm-tide and skew-surge events and identify typical storm tracks and weather types associated with the spatial clusters of extreme events. We find that most extreme storm tides were driven by moderate skew surges combined with high perigean spring tides. The spring–neap tidal cycle, coupled with a moderate surge climatology, prevents successive extreme storm-tide events from happening within 4–10 d of each other, and generally there are at least 10 d between extreme storm-tide events. This is similar to findings from the UK (Haigh et al., 2016), despite NZ having smaller tides. Extreme events more commonly impacted the east coast of the North Island of NZ during blocking weather types, and the South Island and west coast of the North Island during trough weather types. The seasonal distribution of both extreme storm-tide and skew-surge events closely follows the seasonal pattern of mean sea-level anomaly (MSLA) – MSLA was positive in 92 % of all extreme storm-tide events and in 88 % of all extreme skew-surge events. The strong influence of low-amplitude (−0.06 to 0.28 m) MSLA on the timing of extreme events shows that mean sea-level rise (SLR) of similarly small height will drive rapid increases in the frequency of presently rare extreme sea levels. These findings have important implications for flood management, emergency response and the insurance sector, because impacts and losses may be correlated in space and time.

ACS Style

Scott A. Stephens; Robert G. Bell; Ivan D. Haigh. Spatial and temporal analysis of extreme storm-tide and skew-surge events around the coastline of New Zealand. Natural Hazards and Earth System Sciences 2020, 20, 783 -796.

AMA Style

Scott A. Stephens, Robert G. Bell, Ivan D. Haigh. Spatial and temporal analysis of extreme storm-tide and skew-surge events around the coastline of New Zealand. Natural Hazards and Earth System Sciences. 2020; 20 (3):783-796.

Chicago/Turabian Style

Scott A. Stephens; Robert G. Bell; Ivan D. Haigh. 2020. "Spatial and temporal analysis of extreme storm-tide and skew-surge events around the coastline of New Zealand." Natural Hazards and Earth System Sciences 20, no. 3: 783-796.

Journal article
Published: 18 February 2020 in Sustainability
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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.

ACS Style

Ryan Paulik; Scott Stephens; Robert Bell; Sanjay Wadhwa; Ben Popovich. National-Scale Built-Environment Exposure to 100-Year Extreme Sea Levels and Sea-Level Rise. Sustainability 2020, 12, 1513 .

AMA Style

Ryan Paulik, Scott Stephens, Robert Bell, Sanjay Wadhwa, Ben Popovich. National-Scale Built-Environment Exposure to 100-Year Extreme Sea Levels and Sea-Level Rise. Sustainability. 2020; 12 (4):1513.

Chicago/Turabian Style

Ryan Paulik; Scott Stephens; Robert Bell; Sanjay Wadhwa; Ben Popovich. 2020. "National-Scale Built-Environment Exposure to 100-Year Extreme Sea Levels and Sea-Level Rise." Sustainability 12, no. 4: 1513.

Preprint content
Published: 28 January 2020
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ACS Style

Scott Stephens. Reply to Franck Mazas. 2020, 1 .

AMA Style

Scott Stephens. Reply to Franck Mazas. . 2020; ():1.

Chicago/Turabian Style

Scott Stephens. 2020. "Reply to Franck Mazas." , no. : 1.

Preprint content
Published: 28 January 2020
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ACS Style

Scott Stephens. Reply to Anonymous Referee #1, 23 Dec 2019. 2020, 1 .

AMA Style

Scott Stephens. Reply to Anonymous Referee #1, 23 Dec 2019. . 2020; ():1.

Chicago/Turabian Style

Scott Stephens. 2020. "Reply to Anonymous Referee #1, 23 Dec 2019." , no. : 1.

Preprint content
Published: 28 November 2019
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ACS Style

Scott A. Stephens; Robert G. Bell; Ivan Haigh. Supplementary material to "Spatial and temporal analysis of extreme sea level and skew surge events around the coastline of New Zealand". 2019, 1 .

AMA Style

Scott A. Stephens, Robert G. Bell, Ivan Haigh. Supplementary material to "Spatial and temporal analysis of extreme sea level and skew surge events around the coastline of New Zealand". . 2019; ():1.

Chicago/Turabian Style

Scott A. Stephens; Robert G. Bell; Ivan Haigh. 2019. "Supplementary material to "Spatial and temporal analysis of extreme sea level and skew surge events around the coastline of New Zealand"." , no. : 1.

Preprint content
Published: 28 November 2019
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Coastal flooding is a major global hazard, yet few studies have examined the spatial and temporal characteristics of extreme sea level and associated coastal flooding. Here we analyse sea-level records around the coast of New Zealand (NZ) to quantify extreme sea level and skew-surge frequency and magnitude. We identify the relative magnitude of sea level components contributing to 85 extreme sea level and 135 extreme skew-surge events recorded in NZ since 1900. We then examine the spatial and temporal clustering of these extreme sea-level and skew-surge events and identify typical storm-tracks and weather types associated with the spatial clusters of extreme events. We find that most extreme sea levels were driven by moderate skew-surges combined with high perigean-spring tides. The spring–neap tidal cycle, coupled with a moderate surge climatology, prevents successive extreme sea-level events from happening within 4–10 days of each other and generally there are at least 10 days between extreme sea-level events. This is similar to findings from the UK (Haigh et al., 2016), despite NZ having smaller tides. Extreme events more commonly impacted the east coast of the North Island of NZ during Blocking weather types, and the South Island and west coast of the North Island during Trough weather types. The seasonal distribution of both extreme sea-level and skew-surge events closely follows the seasonal pattern of mean sea-level anomaly (MSLA) – MSLA was positive in 92 % of all extreme sea-level and in 88 % of all extreme skew-surge events. The strong influence of low-amplitude (−0.06 to 0.28 m) MSLA on the timing of extreme events shows that mean sea-level rise (SLR) of similarly small height will drive rapid increases in the frequency of presently rare extreme sea levels. These findings have important implications for flood management, emergency response and the insurance sector, because impacts and losses may be correlated in space and time.

ACS Style

Scott A. Stephens; Robert G. Bell; Ivan Haigh. Spatial and temporal analysis of extreme sea level and skew surge events around the coastline of New Zealand. 2019, 2019, 1 -23.

AMA Style

Scott A. Stephens, Robert G. Bell, Ivan Haigh. Spatial and temporal analysis of extreme sea level and skew surge events around the coastline of New Zealand. . 2019; 2019 ():1-23.

Chicago/Turabian Style

Scott A. Stephens; Robert G. Bell; Ivan Haigh. 2019. "Spatial and temporal analysis of extreme sea level and skew surge events around the coastline of New Zealand." 2019, no. : 1-23.

Journal article
Published: 02 September 2019 in International Journal of Climatology
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ACS Style

Laura Cagigal; Ana Rueda; Sonia Castanedo; Alba Cid; Jorge Perez; Scott A. Stephens; Giovanni Coco; Fernando J. Méndez. Historical and future storm surge around New Zealand: From the 19th century to the end of the 21st century. International Journal of Climatology 2019, 40, 1512 -1525.

AMA Style

Laura Cagigal, Ana Rueda, Sonia Castanedo, Alba Cid, Jorge Perez, Scott A. Stephens, Giovanni Coco, Fernando J. Méndez. Historical and future storm surge around New Zealand: From the 19th century to the end of the 21st century. International Journal of Climatology. 2019; 40 (3):1512-1525.

Chicago/Turabian Style

Laura Cagigal; Ana Rueda; Sonia Castanedo; Alba Cid; Jorge Perez; Scott A. Stephens; Giovanni Coco; Fernando J. Méndez. 2019. "Historical and future storm surge around New Zealand: From the 19th century to the end of the 21st century." International Journal of Climatology 40, no. 3: 1512-1525.

Letter
Published: 27 September 2018 in Environmental Research Letters
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Dynamic adaptive policy pathways (DAPP) is emerging as a 'fit-for-purpose' method for climate-change adaptation planning to address widening future uncertainty and long planning timeframes. A key component of DAPP is to monitor indicators of change such as flooding and storm events, which can trigger timely adaptive actions (change pathway/behavior) ahead of thresholds. Signals and triggers are needed to support DAPP—the signal provides early warning of the emergence of the trigger (decision-point), and the trigger initiates the process to change pathway before a harmful adaptation-threshold is reached. We demonstrate a new approach to designing signals and triggers using the case of increased flooding as sea level continues to rise. The flooding frequency is framed in terms of probable timing of several events reaching a specific height threshold within a set monitoring period. This framing is well suited to adaptive planning for different hazards, because it allows the period over which threshold exceedances are monitored to be specified, and thus allows action before adaptation-thresholds are reached, while accounting for the potential range of timing and providing a probability of premature warning, or of triggering adaptation too late. For our New Zealand sea level case study, we expect early signals to be observed in 10 year monitoring periods beginning 2021. Some urgency is therefore required to begin the assessment, planning and community engagement required to develop adaptive plans and associated signals and triggers for monitoring. Worldwide, greater urgency is required at tide-dominated sites than those adapted to large storm-surges. Triggers can be designed with confidence that a change in behavior pathway (e.g. relocating communities) will be triggered before an adaptation-threshold occurs. However, it is difficult to avoid the potential for premature adaptation. Therefore, political, social, economic, or cultural signals are also needed to complement the signals and triggers based on coastal-hazard considerations alone.

ACS Style

Scott A Stephens; Robert Bell; Judy Lawrence. Developing signals to trigger adaptation to sea-level rise. Environmental Research Letters 2018, 13, 104004 .

AMA Style

Scott A Stephens, Robert Bell, Judy Lawrence. Developing signals to trigger adaptation to sea-level rise. Environmental Research Letters. 2018; 13 (10):104004.

Chicago/Turabian Style

Scott A Stephens; Robert Bell; Judy Lawrence. 2018. "Developing signals to trigger adaptation to sea-level rise." Environmental Research Letters 13, no. 10: 104004.

Journal article
Published: 01 April 2018 in Environmental Science & Policy
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Sea-level rise challenges public policy-making because existing planning frameworks and methods are designed to promote certainty using static and time-bound planning and legal instruments. Sea-level rise is a dynamic and uncertain process, which is deeply uncertain towards the latter part of this century and beyond. Communities require decision making approaches that can enable adjustments to policies ahead of damage, without entrenching current exposure to hazards or incurring larger than necessary adjustment costs in the future. We first discuss the nature of the sea-level problem, the policy context that creates decision-making challenges and how they have been typically addressed through policy and practice. Secondly, we show how an assessment and planning approach, designed to address uncertainty and change (the Dynamic Adaptive Policy Pathways (DAPP) planning approach), has been integrated into national guidance for coastal hazard and climate change decision-making in New Zealand. The Guidance integrates hazard and sea-level rise assessments with uncertainty type and with the scale and scope of activity. It is underpinned with values-based community engagement, and uses signals and decision triggers for monitoring and adjusting pathways to meet objectives over time. The applicability of the approach in the Guidance for other policy problems involving uncertainty, is also discussed.

ACS Style

Judy Lawrence; Rob Bell; Paula Blackett; Scott Stephens; Sylvia Allan. National guidance for adapting to coastal hazards and sea-level rise: Anticipating change, when and how to change pathway. Environmental Science & Policy 2018, 82, 100 -107.

AMA Style

Judy Lawrence, Rob Bell, Paula Blackett, Scott Stephens, Sylvia Allan. National guidance for adapting to coastal hazards and sea-level rise: Anticipating change, when and how to change pathway. Environmental Science & Policy. 2018; 82 ():100-107.

Chicago/Turabian Style

Judy Lawrence; Rob Bell; Paula Blackett; Scott Stephens; Sylvia Allan. 2018. "National guidance for adapting to coastal hazards and sea-level rise: Anticipating change, when and how to change pathway." Environmental Science & Policy 82, no. : 100-107.

Journal article
Published: 29 August 2017 in Journal of Marine Science and Engineering
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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.

ACS Style

Scott A. Stephens; Robert G. Bell; Judy Lawrence. Applying Principles of Uncertainty within Coastal Hazard Assessments to Better Support Coastal Adaptation. Journal of Marine Science and Engineering 2017, 5, 40 .

AMA Style

Scott A. Stephens, Robert G. Bell, Judy Lawrence. Applying Principles of Uncertainty within Coastal Hazard Assessments to Better Support Coastal Adaptation. Journal of Marine Science and Engineering. 2017; 5 (3):40.

Chicago/Turabian Style

Scott A. Stephens; Robert G. Bell; Judy Lawrence. 2017. "Applying Principles of Uncertainty within Coastal Hazard Assessments to Better Support Coastal Adaptation." Journal of Marine Science and Engineering 5, no. 3: 40.

Journal article
Published: 01 December 2014 in Journal of Atmospheric and Oceanic Technology
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A technique to produce high-water alerts from coinciding high astronomical tide and high mean sea level anomaly is demonstrated for the Pacific Islands region. Low-lying coastal margins are vulnerable to episodic inundation that often coincides with times of higher-than-normal high tides. Prior knowledge of the dates of the highest tides can assist with efforts to minimize the impacts of increased exposure to inundation. It is shown that the climate-driven mean sea level anomaly is an important component of total sea level elevation in the Pacific Islands region, which should be accounted for in medium-term (1–7 months) sea level forecasts. An empirical technique is applied to develop a mean sea level–adjusted high-water alert calendar that accounts for both sea level components and provides a practical tool to assist with coastal inundation hazard planning and management.

ACS Style

Scott A. Stephens; Robert Bell; Douglas Ramsay; Nigel Goodhue. High-Water Alerts from Coinciding High Astronomical Tide and High Mean Sea Level Anomaly in the Pacific Islands Region. Journal of Atmospheric and Oceanic Technology 2014, 31, 2829 -2843.

AMA Style

Scott A. Stephens, Robert Bell, Douglas Ramsay, Nigel Goodhue. High-Water Alerts from Coinciding High Astronomical Tide and High Mean Sea Level Anomaly in the Pacific Islands Region. Journal of Atmospheric and Oceanic Technology. 2014; 31 (12):2829-2843.

Chicago/Turabian Style

Scott A. Stephens; Robert Bell; Douglas Ramsay; Nigel Goodhue. 2014. "High-Water Alerts from Coinciding High Astronomical Tide and High Mean Sea Level Anomaly in the Pacific Islands Region." Journal of Atmospheric and Oceanic Technology 31, no. 12: 2829-2843.

Proceedings article
Published: 28 September 2004 in Estuarine and Coastal Modeling (2003)
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Two- and three-dimensional hydrodynamic models of the Hauraki Gulf (Auckland, New Zealand) have been developed over several years, verified against several observational datasets for currents, temperature and tides. The modeling has reached a stage where it is now being used in a wide range of applications to support resource management and maritime operations. The underpinning modeling relates to both tidal and wind-generated currents and circulation in the Gulf over a variety of timescales from hours to multiple decades. Applications of the model described in this paper relate to sustainability of fisheries and aquaculture, surface wind drift (search & rescue, outfall plumes, water quality) and yacht racing (e.g., Americas Cup). The next stage in utilizing the models is the development of a nowcasting and forecasting hydrodynamic system.

ACS Style

Robert G. Bell; John W. Oldman; Scott A. Stephens. Recent Applications of 3D Wind-Driven Circulation Modeling to a Semi-Enclosed Sea: Hauraki Gulf, New Zealand. Estuarine and Coastal Modeling (2003) 2004, 288 -307.

AMA Style

Robert G. Bell, John W. Oldman, Scott A. Stephens. Recent Applications of 3D Wind-Driven Circulation Modeling to a Semi-Enclosed Sea: Hauraki Gulf, New Zealand. Estuarine and Coastal Modeling (2003). 2004; ():288-307.

Chicago/Turabian Style

Robert G. Bell; John W. Oldman; Scott A. Stephens. 2004. "Recent Applications of 3D Wind-Driven Circulation Modeling to a Semi-Enclosed Sea: Hauraki Gulf, New Zealand." Estuarine and Coastal Modeling (2003) , no. : 288-307.