Skip to main content.

Executive Summary

Risks related to coastal hazards are not new to planners and resource and hazard managers of New Zealand local government. However, the foreseeable future provides some challenges for those tasked with the sustainable management of coastal margins.

A high proportion of New Zealand’s urban development has occurred in coastal areas. Some of this development has been located in areas that are vulnerable to coastal hazards such as coastal erosion and inundation. In recent years, coastal development and associated infrastructure have intensified, and property values have increased enormously. As development and property values in coastal margins increase, the potential impacts and consequences of coastal hazards also increase. Managing this escalating risk over the coming decades now presents a significant challenge for planning authorities in New Zealand.

Climate change will exacerbate existing coastal hazards

Risk will be exacerbated in many places by the effects of climate change. Climate change will not introduce any new types of coastal hazards but it will affect existing coastal hazards by changing some of the hazard drivers. It will exacerbate coastal erosion and inundation on many parts of the New Zealand coast, further increasing the impacts of coastal hazards on coastal development.

Local government is required to take account of climate change

Climate change effects are gradual, but many land-use planning decisions have long-term implications because of the permanency of structures (eg, buildings, roads, network utilities). While it is a requirement under the planning framework of the Resource Management Act 1991, it is also wise and good business practice to consider climate change implications in coastal planning,

What this Guidance Manual does

This Guidance Manual has been written primarily to support local authorities (policy, planning, consents, building and engineering staff) in dealing with some of these challenges. It provides best practice information and guidance to strengthen the integration of coastal hazards and climate change considerations in land-use planning and during resource consent decision-making. More specifically, the Guidance Manual:

  • provides information on the key effects of climate change on coastal hazards

  • provides a risk assessment framework for incorporating coastal hazard and climate change considerations into the decision-making processes associated with policy development, planning and the awarding of resource consents

  • promotes the development of long-term adaptive capacity for managing coastal hazard risk through the adoption of adaptive management and no-regrets response options.

What’s new in this edition?

This is the second edition of this Guidance Manual, and it supersedes the first edition published in 2004. This edition’s publication follows an updated assessment of the science of climate change by the Intergovernmental Panel on Climate Change (IPCC) in 2007.

The IPCC’s Fourth Assessment, 2007 concluded that most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. The Fourth Assessment also showed that it is likely that anthropogenic warming has had a discernable influence on many physical and biological systems. The IPCC concluded that continued emission of greenhouse gases at or above current rates would cause further warming; this could induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.

This conclusion may have significant implications for some coastal infrastructure and development, especially those that will need to cope with climate conditions in 50–100 years’ time or even after that time.

The main changes in this edition of the Guidance Manual are:

  • it updates the climate change science and provides guidance and recommendations relevant to coastal margin issues in New Zealand

  • there is a new chapter on local government response to climate change, emphasising how climate change adaptation fits within the key principles of local government actions (Chapter 4)

  • there are minor revisions to the risk assessment process to enable local authorities to better characterise coastal hazard risk (Chapter 5)

  • the chapter on managing coastal hazards and climate change risk has undergone major revision (Chapter 6)

  • supporting material in the appendices has been revised and updated where necessary.

The structure and format of the Guidance Manual have also been significantly revised in response to stakeholder feedback, to make the document and the information in it more accessible to the user.

Sea-level rise

Relative mean sea levels have risen by 0.16 m on average over the last 100 years around New Zealand. This is comparable to global rates of mean sea-level rise over the same time period.

Sea-level rise projections for the next 100 years are based on different computer simulations of the atmosphere and ocean for a range of emission scenarios (ie, different greenhouse gas emission scenarios based on how the human race may live over the next 100 years). For New Zealand, there may be some variation in the rate of future sea-level rise compared to the global average, but these differences are not yet well defined.

In its Fourth Assessment Report, the IPCC has found that “Because understanding of some important effects driving sea-level rise is too limited, this report does not assess the likelihood, nor provide a best estimate or an upper bound for sea-level rise”. While there are uncertainties associated with the science around sea-level changes, national and local governments and individuals must continue to make decisions that either implicitly or explicitly make assumptions about what this rise will be over a planning timeframe.

This Guidance Manual advocates the use of a risk assessment process to assist incorporating sea-level rise and the associated uncertainties, within local government planning and decision-making. This requires a broader consideration of the potential impacts or consequences of sea-level rise on a specific decision or issue. Rather than define a specific climate change scenario or sea-level rise value to be accommodated, it is recommended in this Guidance Manual that the magnitude of sea-level rise accommodated is based on the acceptability of the potential risk.

To aid this risk assessment process, this Guidance Manual recommends that allowance for sea-level rise is based on the IPCC Fourth Assessment Report; and that consideration be given to the potential consequences from higher sea-levels due to factors not included in current global climate models.1

For planning and decision timeframes out to the 2090s (2090–2099):

a. a base value sea-level rise of 0.5 m relative to the 1980–1999 average should be used, along with

b. an assessment of the potential consequences from a range of possible higher sea-level rises (particularly where impacts are likely to have high consequence or where additional future adaptation options are limited). At the very least, all assessments should consider the consequences of a mean sea-level rise of at least 0.8 m relative to the 1980–1999 average. Guidance on potential sea-level rise uncertainties is provided within the Guidance Manual to aid this assessment.

For planning and decision timeframes beyond 2100 where, as a result of the particular decision, future adaptation options will be limited, an allowance for sea-level rise of 10 mm per year beyond 2100 is recommended (in addition to the above recommendation).

Other coastal hazard drivers

Climate change will also impact on other coastal hazard drivers, such as tides, storm surge, waves, swell and coastal sediment supply. The potential changes and their impacts are at present much less well understood, but this manual provides pragmatic guidance informed by expert judgement and the current state of scientific knowledge.

Tide range and relative frequency of high tides

The present Mean High Water Spring level will be exceeded much more frequently by high tides in the future, particularly on sections of the coast where the tide range is relatively small (compared with those sections of the coast where the tide range is relatively large). Sea-level rise will have a greater influence on storm inundation and rates of coastal erosion on the central parts of the east coast and Cook Strait / Wellington areas than on coastal regions with larger tidal ranges (eg, west coast).

Storms

The IPCC Fourth Assessment, 2007 suggests in general a likely:

  • decrease in the total number of extra-tropical cyclones

  • slight poleward shift of the storm track and associated precipitation, especially in winter

  • increased number of intense cyclones and associated strong wind, particularly in winter over the South Island.

Changes in storm conditions will affect coastal margins around New Zealand through possible changes in the frequency and magnitude of storm surges and storm tides, and in swell and wave conditions.

Storm surge and storm tides

This Guidance Manual recommends that planners assume that storm tide (ie, extreme) levels will rise at the same rate as mean sea level until more certainty emerges on likely changes to wind and central pressures associated with storm systems.

Wave climate

Expected changes in wind and atmospheric patterns, storms and cyclones around New Zealand and the wider southwest Pacific and Southern Ocean regions also have the potential to change the wave climate experienced around New Zealand. In turn, this will influence patterns of coastal erosion and the movements of beach and nearshore sediments within coastal zones. Little definitive guidance can be provided on how wave climates around New Zealand will change and what this may mean for coastal erosion and inundation.

This Guidance Manual sets out recommended assumptions for carrying out ‘what if’ scenarios for wave modelling, depending on the location of the coastline in question and whether it is exposed to, or sheltered from, oceanic swell.

Sediment supply to the coast

The potential for change in sediment supply will vary from place to place, with changes in the west–east gradient in rainfall (wetter in the west and drier in the east) likely to be a significant factor, along with increased rainfall intensities during severe rainstorms. Where changes in sediment delivery to the coast are an important consideration, sediment delivery from river systems will need to be determined based on detailed specific investigations and an assessment of how sediment volumes may change under future rainfall projections carried out.

Risk assessment process

The magnitude of the impacts of climate change on coastal margins will differ between regions and even between localities within regions. Such impacts will depend on the complex interaction between the localised impacts of climate change on the physical drivers that shape the coast, the natural characteristics of the coast and the influence that humans have had or are having on the coast. This Guidance Manual provides a risk assessment process to assist local authority staff in ensuring that coastal hazards, and the effects that climate change may have on these coastal hazards, are appropriately taken into account in policy, planning and resource consent decision-making. The assessment process permits a structured approach to thinking about, and working through, coastal hazard and climate change issues.

The risk assessment process and use of up-to-date knowledge of climate change can assist local government in helping communities adapt, especially through their regional and district plans. The risk assessment process fits comfortably into plan preparation and review, and the resource consent process.

Principles in managing coastal hazard risk

This Guidance Manual recommends that local authorities incorporate the following principles into all aspects of their decision-making about coastal margins:

  • precautionary approach: A precautionary approach is adopted when making planning decisions relating to new development, and to changes to existing development within coastal margins. Decision-making takes account of the level of risk, utilises existing scientific knowledge and accounts for scientific uncertainties

  • progressive risk reduction: New development is not exposed to, and does not increase the levels of, coastal hazard risks over their intended serviceable lifetime. Progressively, the levels of risk to existing development are reduced over time

  • coastal margin importance: The dual role of natural coastal margins as the fundamental form of coastal defence and as an environmental, social and cultural resource is recognised in the decision-making processes and, consequently, natural coastal margins are secured and promoted

  • integrated, sustainable approach: An integrated and sustainable approach to the management of development and coastal hazard risk is adopted, which contributes to the cultural, social and economic wellbeing of people and communities.

To achieve these principles, local government will need to:

  • identify and effectively account for coastal hazards, vulnerabilities and potential consequences within coastal margins

  • communicate effectively to build community awareness, and public and political support for activities associated with coastal hazard risk planning

  • engage the community in consultation and participation in achieving effective community planning outcomes.

1 Such factors relate to uncertainties associated with increased contribution from the Greenland and Antarctica ice sheets; carbon cycle feedbacks; and possible differences in mean sea level when comparing the New Zealand region with the global average.

[ |