Risk-based Approach to Planning

Principles for planning approaches

These guidelines are based on three overarching principles:

  1. Gathering accurate natural hazard information: Identifying and accurately locating hazard sites or zones on planning maps is essential for communicating and mitigating hazard risk. Collecting information often requires specialised technical knowledge and surveys. Maps showing the location of hazards in the vicinity of a property must be developed at an appropriate scale. As the existence of a particular hazard may have a major effect on a decision to purchase or build on a property, all information on hazards should be as accurate as technology and resources permit.
  2. Planning to avoid natural hazards before development and subdivision: Natural hazards can be avoided by preventing building and development on known hazard areas. Where natural hazards cannot be avoided, mitigation measures such as reducing risk through engineering works should be instigated. For example, the developer of a new subdivision may be required to avoid building directly on a landslide path and to mitigate its risk to other areas of the development through retaining structures. Whether outright avoidance or mitigation provides the best means in each case should be considered in terms of achieving an acceptable long-term solution. This consideration may include whether a decision now will create expectations for further development that would become unacceptable.
  3. Taking a risk-based approach in areas already developed or subdivided: Land already subdivided, developed or used for specified activities will have some existing use rights attached. However, further development or changes in use should require that any increase in hazard risk is considered. Planning for land use in a hazard zone helps to avoid or mitigate the increased risks from natural hazards caused by land-use intensification (such as urban infill) and inappropriate building or use.
    ISO 31000: 2009, Risk Management – Principles and Guidelines provides principles, definitions and a process for managing risk. Key steps in the process (establishing context, risk identification, analysis, and evaluation) are summarised below. The remainder of the guidance note focuses on ways to manage or treat natural hazard risks (including the RMA tools to manage specific hazards).

(a) Establishing the context: Applying the risk management process to natural hazards management depends very much on the context, for example working within an RMA plan review process or the consenting process. It will also be influenced by the specific nature of the hazard, the community context and those directly affected or interested parties. The application of the process can therefore vary and organisations should adapt it to suit their particular needs. For assessing natural hazards in a planning context, the standard has been tailored and is briefly described below. Identifying all stakeholders and developing a communication plan are important parts of this process.

More detailed information on selecting and applying systematic techniques for risk assessment is contained in IEC 31010: 2009 – Risk Assessment Techniques.

(b) Identification of risks: Identifying the 'hazardscape' is an important step to understanding the risks posed to communities by natural hazards. For those planning under the RMA, identifying the likely risks facing a district, city, or region is the first part in establishing whether issues, objectives, policies or rules need to be included for them in RMA plans. For those working on resource consents, checking for the presence of natural hazards is important in both preparing and considering assessments of environmental effects in accordance with Schedule 4 (clause 2(f)).

Hazard mapping

A starting point to identify hazards risks is a scan of hazard information, including recent hazard events (such as floods and slips) for the area. It is good practice for councils to map known hazards in their areas to help with plan preparation, and enable those processing consents to quickly understand the hazards that may impact on a proposal, or that may be exacerbated by a proposed activity or development.

The National Hazardscape Report, produced in 2007, provides a definitive snapshot of the knowledge on New Zealand's hazards and risks at that point in time.

In identifying risks through hazard mapping local authorities should:

  • adopt an all-inclusive approach to hazard mapping, starting with the regional setting, then focusing into the detailed scale
  • consider appropriate scales for hazard mapping to ensure information is portrayed accurately and not misrepresented. Suggested scales are:
    • National (1:1,000,000)
    • Regional (1:100,000 to 1:500,000) - QMAP series
    • Medium (1:25,000 to 1:50,000) - typically municipal or small metropolitan areas
    • Small (1:5,000 to 1:15,000) - typically site or property level This scale is recommended for district plan hazard mapping
  • map hazards at a scale that is appropriate to the end-use purpose (the end-use maps, for example those used in district plans, should not be significantly different to the scale the hazard was originally mapped at to avoid errors or misrepresentation of the information contained in the maps)
  • consider scale when combining hazard maps with other types of maps
  • ensure that hazard mapping information is not distorted when using GIS by limiting the use of the zoom tool on GIS systems to the scale the original hazard was mapped at
  • be mindful that hazard information available to the public should have clear statements as to its purpose and level of accuracy, any other limitations that are relevant, and may include disclaimers in this regard

The use of aerial photography

Aerial photography is useful for identifying various hazards, such as active faults and landslides. Comparing aerial photographs of an area over time can give an indication of the frequency and extent of various events. Different types of photography, including vertical (or oblique) aerial photos and orthophotos, provide different hazards information.

It is important to use photographs from different periods spanning as much time as possible, as land development can often conceal the presence of features (for example, earthworks can modify an environment so that the original features, such as fault lines and landslides, are 'removed' from the site).

Types of photography useful in natural hazard management

Vertical (or oblique) aerial photos: when taken as a series, these can be used to illustrate the features of concern, and highlight differences that have occurred over a period of time (for example, the erosion of coastlines over time).

Orthophotos: aerial photos with the distortion removed, and related to specific points on the ground. When overlaid with LIDAR (Light Detection and Ranging: a system used to measure the elevation of a surface, with greater than 1 metre accuracy), an accurate representation of the land use can be made in relation to natural hazards.

Orthophotos overlaid with LIDAR have the advantage of being able to be vertically exaggerated and manipulated as required.                         

 Whangaehu River Valley

Path of the 2007 lahar down the Whangaehu River valley

The photograph above shows the Whangaehu River channel at the location of the Round the Mountain Track (Tongariro National Park). It shows the path the 2007 lahar took down the Whangaehu River valley. This is an example of a digitally enhanced map from a LIDAR survey draped with a vertical orthophoto.


Identify natural hazard risk level

As part of risk identification ask questions about each of the key activities, projects or processes.

Good quality information is important in identifying risks. The starting point for risk identification is historical information and discussions with a wide range of stakeholders about historical, current and evolving issues. People involved in identifying risks are knowledgeable about the detailed aspects of the risk identification being undertaken. Identifying risks can also require imaginative thinking and appropriate experience. Allow for the pooling of experience. Team involvement helps build commitment and ownership into the risk management process and helps ensure that risks to different stakeholders are considered where appropriate.

In order to understand the risk a hazard may pose, start by establishing the hazardscape (from hazard identification studies), location, social environment, economic environment, etc. Alternative information sources can be used in the absence of detailed hazard studies. Alternative sources of information could include:

  • historical photographs, newspaper reports and firsthand accounts of prior events, and about changes to the environment that may mask or alter this pre-existing hazard
  • information held by local libraries
  • information collected for other purposes such as university research
  • information collected by old catchment boards
  • historical records for organizations such as the Ministry of Works and Development

Once the hazardscape has been defined, the hazard risks posed by different activities, processes or projects in a particular area can then be identified.

(c) Risk analysis: Having established the hazards that may be applicable to a given area, district or region the next step is to determine the significance of hazard risk. A risk analysis is often required to:

  • obtain more information about the consequences or the likelihood of decisions so that priorities are based on information and data rather than guesswork
  • better understand the risk and its causes so that treatment plans can be directed at true rather than superficial causes of problems
  • help people choose between options where each has different costs and benefits and potential opportunities and threats
  • provide a better understanding of risk to individuals who must operate with the risks
  • provide an understanding of residual risk after treatment strategies have been applied

Risks that are considered to be high or significant may require further evaluation and possible treatment (actions to avoid, remedy or mitigate them). Conversely, for some hazards the risk level may be low so as to not require immediate, or further, consideration.

Risk analysis establishes an understanding of the level of risk and its nature. Aside from the absolute level of risk, analysis will help to set treatment priorities and options. The level of risk is determined by combining consequence (potential impact) and likelihood (probability).

Risk analysis can be performed either qualitatively (using words to describe the magnitude of potential consequences and the likelihood that those consequences will occur), quantitatively (uses numerical values for both consequences and likelihood) or a combination of both. Suitable scales and methods for combining consequence and likelihood should be consistent with the criteria defined when establishing the context. For more technical analysis, the nature of the data and required output will dictate the required analysis methods.

Decisions as to which risk analysis method should be used are influenced by the context, objectives of the risk analysis and available resources. Some risks may need to be examined in detail and a risk analysis may be undertaken to varying degrees of detail depending upon the risk, purpose, and the information, data and resources available.

The order of complexity and costs of analyses, in ascending order, is qualitative, semi-quantitative and quantitative. In practice, qualitative analysis is often used first to obtain a general indication of the level of risk and to reveal the major risk issues. It can be used as a way of screening overall hazard risks and assigning priority for those that need further evaluation. Later it may be necessary to undertake more specific, quantitative, analysis on the major risk issues.

Qualitative analysis: Qualitative analysis uses words to describe the magnitude of potential consequences and the likelihood that those consequences will occur. These descriptions can be adapted or adjusted to suit the circumstances, and different descriptions may be used for different risks. Qualitative analysis may be used:

  • as an initial screening activity to identify risks which require more detailed analysis
  • where this kind of analysis is appropriate for decisions
  • where the numerical data or resources are inadequate for a quantitative analysis.

Qualitative analysis should be informed by factual information and data where available.

Semi-quantitative analysis: In semi-quantitative analysis, qualitative scales such as those described above are given values. The objective is to produce a more expanded ranking scale than is usually achieved in qualitative analysis, without reaching the level of highly precise and accurate values for risk such as is attempted in quantitative analysis. However, since the value allocated to each description may not bear an accurate relationship to the actual magnitude of consequences or likelihood, the numbers should only be combined using a formula that recognises the limitations of the kinds of scales used. Care must be taken with the use of semi-quantitative analysis because the numbers chosen may not properly reflect relativities and this can lead to inconsistent, anomalous or inappropriate outcomes. Semi-quantitative analysis may not differentiate properly between risks, particularly when either consequences or likelihood are extreme.

Quantitative analysis: Quantitative analysis uses numerical values (rather than the descriptive scales used in qualitative and semi-quantitative analysis) for both consequences and likelihood using data from a variety of sources. The quality of the analysis depends on the accuracy and completeness of the numerical values and the validity of the models used. Consequences may be determined by modelling the outcomes of an event or set of events, or by extrapolation from experimental studies or past data. Consequences may be expressed in terms of monetary, technical or human impact criteria. In some cases, more than one numerical value is required to specify consequences for different times, places, groups or situations.

The way in which consequences and likelihood are expressed, and the ways in which they are combined to provide a level of risk, will vary according to the type of risk and the purpose for which the risk assessment output is to be used. The uncertainty and variability of both consequences and likelihood should be considered in the analysis and communicated effectively.

Outputs of risk assessments can include susceptibility maps and matrices. For example, susceptibility maps for landslips or slumping can rank slope stability of an area into categories that range from stable to unstable. A susceptibility map can show where landslides may form.

Sensitivity analysis: Since some of the estimates made in risk analysis are imprecise, a sensitivity analysis should be carried out to test the effect of uncertainty in assumptions and data. A sensitivity analysis is also a way of testing the appropriateness and effectiveness of potential controls and risk treatment options. Consider engaging someone experienced in undertaking sensitivity analysis to undertake this task.

The example of a sensitivity analysis below shows bars of uncertainty for the tsunami risk. The dashed lines show the uncertainty at the 16th and 84th percentiles. The tsunami risk for each of the main centres was presented with these uncertainty bars in the Review of Tsunami Hazard and Risk in New Zealand (see the Ministry of Civil Defence and Emergency Management website).

The example of a sensitivity analysis 

(d) Risk evaluation and developing a treatment plan: Having established the presence of a natural hazard, and an approximation as to the level of risk associated with that hazard, the third step is to evaluate options in regard to managing risk (including the 'do nothing option'). This stage of the process helps inform s32 evaluation reporting, plan objectives and policies, or may form part of the process in considering whether avoidance or mitigation options proposed in a resource consent application are appropriate.

A s32 evaluation is a key requirement throughout the plan-making process and the Resource Management Amendment Act 2013 provides greater guidance and specificity about what is required in s32 reporting, particularly for the assessment of costs and benefits. These changes come into force on 3 December 2013 (3 months after Royal Accent) and require s32 evaluations to now:

  • specifically assess the benefits and costs of the environmental, economic, social and cultural effects
  • assess the opportunities for providing or reducing economic growth and employment
  • quantify the costs and benefits of provisions, where practicable.

The s32 evaluation process will help identify the degree and nature of issues and the effects and provide a framework from which to consider and test appropriate objectives, policies, and methods in plans (refer to the Ministry for the Environment's Fact Sheet 6: Section 32 of the RMA for further information on the new requirements as a result of the Resource Management Amendment Act 2013).

Evaluating options involves weighing the relative costs of each option with the losses that will occur if the risk is not treated. The costs and losses to all parties should be considered, noting also that who benefits and who pays may vary across options. Some costs may be indirect, for example loss of business opportunities during an event. Also maintaining a readiness and response capability imposes a cost and the trade-offs between reliance on this capability and undertaking reduction should also be considered. Any losses realised or benefits gained from avoiding or reducing risk, may only accrue over time. As such, the likely costs and benefits arising over the full 'lifetime' of each option should be analysed in Net Present Value terms.

For those preparing plans and strategies, determining acceptable levels of risk and willingness to pay for risk reduction across a community will require effective communication and consultation processes. These processes begin with determining the communities' goals for hazard risk reduction and end with evaluating outcomes.

Decisions should take account of the wider context of the risk and include consideration of how tolerable the risks are to various parties who receive no benefit from them. In some circumstances, the risk evaluation may lead to a decision to undertake further analysis.

One of the most difficult problems concerning natural hazards is dealing with urban areas where buildings are constructed on, or close to, a particular hazard, such as an active fault, floodway, or landslide. The ideal approach in this situation would be to avoid further development in high-risk areas, to limit existing-use rights to rebuilding (i.e. replacement buildings can only be the same scale and density as those existing), and to limit the use of buildings. Non-regulatory methods can actively discourage people rebuilding and encourage them to move elsewhere.
The most realistic approach, however, is to accept the status quo whilst ensuring that:

  • any further development and use of buildings is consistent with the level of risk posed
  • district plan maps clearly show hazard zones, and information for individual properties is placed on LIM reports.

Non-regulatory approaches, such as hazard education and engagement programmes, also ensure that landowners and building occupiers are made aware of the hazard, and of the probability of hazard events occurring. Hazard education initiatives must reflect the complex socio-economic nature of communities; programmes need to target a range of at-risk groups, and may require a mix of approaches.

The principles recognise that a different planning approach is needed for an area that has not been developed than for an area that has been developed or subdivided (or where there is an expectation to build). These principles are underpinned by a risk-based approach.

Risk prioritisation

A range of methods are available to prioritise risks. Generally, councils have used the Seriousness, Manageability, and Growth (SMG) analysis for prioritising hazards in their CDEM Group plans, based on the Risk Management Standard AS/NZ ISO 31000. There are also some other variations being used.

The SMG model is used to compare and prioritise hazards based on the seriousness, manageability, and growth characteristics of each hazard. SMG can also be used as a method of qualitative risk calculation.

Ideally, if undertaking a risk prioritisation process, councils should check what methods are contained in their CDEM Plan and adopt the same methodology where practicable. This will make it easier to ensure that the key priorities are the same under both CDEM and RMA processes (while recognising that a CDEM Plan is going to be wider than just natural hazards).

Residual risk

Residual risk is the risk that remains after all treatment steps are in place, in other words the fatalities, injuries and destruction that must be accepted either by default or because the costs of treatment are considered too high, and/or such outcomes are too uncertain or rare to plan for.

Supporting materials for risk management processes

The 2009 Australian/New Zealand Risk Management Standard – Principles and Guidelines 31000 provides organisations with guiding principles, a generic framework and a process for managing risk. I includes 11 risk management principles an organisation should comply with, and a management framework for the effective implementation and integration of these principles into an organisation’s management system.

An overview of the risk management process

An overview of the risk management process


EXPLANATION: This figure shows the risk management process, with the key actions (establish the context, identify risks, analyse risks, evaluate risks and treat risks) shown as five separate boxes. The monitoring and reviewing, and communicating and consulting of the key actions are shown to either side to indicate that they take place throughout the process.

The final step of the process, treating risks feeds directly into the monitoring and review process which feeds into the next round of risk management through providing information on the context of the risk. Note that the three middle steps (identifying, analysing, and evaluating the risk) are all considered to be part of the risk assessment stage (as indicated by the stippled box in the centre of the diagram).

The risk management process for landslide hazard



  • Where are the landslides in the district or region?


  • What is the likelihood of a landslide in the district? (landslide recurrence interval)  
  • What is the nature of the landslide? (type, size, mechanism, complexity)


  • What are the elements at risk at the proposed development site? (people, recurrence assets)  
  • What is the construction type? (building importance category)


  • Likelihood of hazard x consequences?



  • How does the risk compare with other hazards?  
  • Is the risk acceptable?
  • Are there alternatives or options?



  • What action should be taken to avoid or mitigate the risk within the landslide hazard area?  
  • Regulatory planning methods
  • Non-regulatory methods  
  • Limiting the risk posed by the building


  • Are our outcomes being achieved?  
  • Is new information available?
  • Does the district plan need to be updated?

EXPLANATION: The diagram above shows how the risk management approach can be applied to managing landslide hazards. The diagram is divided into three main boxes (labelled 'risk analysis', 'risk evaluation', and 'risk management' respectively). Within these three boxes there are seven steps that need to be undertaken.

Questions to assist in framing key hazard issues

In considering how to manage risks associated with natural hazards, the following questions can be of assistance in guiding decision makers:

  • What is the source of each risk?
  • What might happen that could:
    • increase or decrease the effective achievement of objectives of the risk management process?
    • make the achievement of the objectives more or less efficient (financial, people, time)?
    • cause stakeholders to take action that may influence the achievement of objectives?
    • produce additional benefits?
  • What would the effect on risk management objectives be?
  • When, where, why, how are these risks (both positive and negative) likely to occur?
  • Who might be involved or impacted?
  • What controls presently exist to treat this risk (maximise positive risks or minimise negative risks)?
  • What could cause the control not to have the desired effect on the risk?
  • What is the reliability of any information we have?
  • How confident are we that the list of risks is comprehensive?
  • Is there a need for additional research into specific risks?
  • Are the objectives and scope covered adequately?
  • Have the right people been involved in the risk identification process?

The SMUG model: a basis for hazard prioritisation

The SMG model was defined in the CDEM Group Plan review Director's Guideline on CDEM Groups (DGL 09/09). The definitions of seriousness, manageability and growth are as follows.

The relative impact in terms of people and/or dollars. The number of lives lost and potential for injury, and the physical, social and economic consequences of a hazard event were specifically considered while rating seriousness.

Manageability includes both a measure of how difficult a hazard's risks are to address and a measure of the cross-sector management effort being applied to hazards across the '4 Rs'.

The rate at which the risk from the hazard will increase through either an increase in the probability of the extreme event occurring, an increase in the exposure of the community, or a combination of the two.

Method for rating seriousness

Seriousness is defined as the relative impact in terms of people and/or dollars. When rating the seriousness of a hazard event, the following consequences are specifically considered:

  • human (potential number of lives lost and potential for injury)
  • economic
  • social
  • infrastructure
  • geographic.

For each of the applicable hazard types a seriousness score of 0-5 is assigned to each of the above five consequences. These are then averaged to give a total seriousness score.

Method for rating manageability

Manageability is defined as the relative ability to mitigate or reduce the hazard.

Manageability includes both a measure of how difficult a hazard's risks are to address and a measure of the cross-sector management effort being applied to hazards across the '4 Rs' directly or indirectly assisting in reduction of risk. The level of difficulty may, in some cases, be inversely proportional to the level of management effort, particularly where a hazard appears too big to address, and therefore little effort is being applied. Conversely, a lot of effort may be expended on a relatively easily managed hazard.

Method for rating growth

Growth is defined as the rate at which the risk from the hazard will increase through either an increase in the probability of the extreme event occurring, an increase in the exposure of the community or a combination of the two.

Assign a low, medium or high rating for the 'growth' criteria using the descriptions below.

Rate of growth

Low (1): risk increases from either an increase in the probability of an extreme event occurring or an increase in the exposure of the community.

Moderate (2): risk increases from both an increase in the probability of an extreme event occurring and an increase in the exposure of the community at a low-moderate rate.

High (3): risk increases from both an increase in the probability of an extreme event occurring and an increase in the exposure of the community at a high rate.

Note of caution: difficulties with prioritising hazards

There are several difficulties associated with assigning ratings to each of the above SMG criteria:

  • the seriousness rating assigned to a given hazard depends upon the magnitude of the hazard event under consideration.
  • there may be a lack of sufficiently robust quantitative data to evaluate all hazards and risks, particularly in ways that enable comparisons across hazards and risks. Lack of quantitative data means that evaluations of hazard consequences or risks may have to be qualitative only. Including advice from as many different experts as possible will strengthen such evaluations.

A toolbox for risk based land use planning for natural hazards

GNS Science has developed a toolbox which aims to support risk-based land use policy and plan development in local government. It offers a new approach where consequences of natural hazard events are the focus. It presents techniques, practice steps and options for enabling local government to review multiple natural hazard risks, both within councils and with external stakeholders. The toolbox is available on the GNS Science website.