Home / RBP / Risk based planning / A toolbox / Assumptions, limitations and uncertainties

Assumptions, limitations and uncertainties

A number of assumptions have been made in the development of the risk-based approach. These are outlined for each step of the approach, along with limitations and uncertainties.

STEP 1: Know your hazard

Assumptions

  • Any hazard assessment will be based on the best available knowledge at the time.
  • A hazard assessment report will include assumptions, limitations and uncertainties.

Limitations

  • If focussing on a single hazard, need to be aware of other hazards that can result i.e. cascading hazards. For example, if just assessing the earthquake hazard, need to be aware that the earthquake may trigger land instability, liquefaction, tsunami. These need to be included in the assessment in order for their consequences to be assessed.

Uncertainties

  • Any hazard assessment will involve uncertainties around the nature of the hazard.
  • If modelling is involved, uncertainties within the model need to be acknowledged.

STEP 2: Determine severity of consequences

Assumptions

  • A robust public engagement and risk communication process needs to be implemented alongside the table and associated process (provided as part of the Envirolink toolkit). This is to ensure that the community and key stakeholders are informed of the process and that the council can receive constructive and useful feedback. This public engagement process helps inform the acceptable, tolerable and intolerable risk levels and the associated consent categories.
  • The hazard information a Council has available is sufficiently accurate to allow for the calculation of the consequences from the hazard event. To be able to use the consequence table, the hazard information needs to be relatively detailed and scientifically robust. Furthermore, in order to be able to populate some of the consequence table categories, specialist information may be required (for example a risk modeller may be required to determine the number of deaths from a natural hazard scenario).
  • It is appropriate to consider mitigation measures where they reduce the consequences from an event. For example, an activity may be considered ‘moderate’ (using first past the post), but with effective mitigation the consequences could be reduced to ‘minor’.
  • For the majority of the consequences, the severity of impact is calculated based on the level of consequences in hazard zones (for example the extent of an area affected by flooding). The use of hazards zones is recommended as it prevents the effects of the natural hazard event from being diluted by including buildings from a wider geographical area that are not be impacted from the hazard. The exception to this is the calculation of consequences from the damage to lifelines. Lifelines are a network and therefore if one area of the lifeline is damaged, then it is likely to have an effect on people and property outside of the identified hazard zone.
  • Not all hazard events will result in catastrophic consequences. Many natural hazard events may only result in moderate of major consequences (e.g. flood vs earthquake).
  • The consequence table focuses on the primary effects associated with the natural hazard event (i.e. the immediate damage). It does not take into account secondary effects (for example the. loss of employment due to damage to buildings).
  • For the built environment consequence categories, the severity of impact is based on whether the building is functionally compromised. Functionally compromised means whether the building is able to be continued to be used immediately after the event for its intended use. For example, if an apartment building does not have a water supply, it is unable to be used for residential accommodate due to fire fighting requirements. As such, the functionality of this building has been compromised by the natural hazard event.
  • Critical buildings are buildings which have a post-disaster function. These include:
    • Buildings and facilities designed as essential facilities;
    • Buildings and facilities with special post-disaster function;
    • Medical emergency or surgical facilities;
    • Emergency service facilities such as fire and police stations;
    • Designated emergency shelters;
    • Designated emergency centres and ancillary facilities; and
    • Buildings and facilities containing hazardous materials capable of causing hazardous conditions that extends beyond the property boundaries.
  • Social and cultural buildings are buildings that are of social and cultural importance. These include:
    • Places of worship;
    • Museums;
    • Art galleries;
    • Marae; and
    • Educational facilities.

Sporting/recreational facilities are not included as these are often specifically located in hazardous areas e.g. flood paths. In some instances it is considered good practice to locate these types of activities in hazard zones, as the consequences associated with these activities can be low.

  • The built environment covers all buildings not considered to fall under the definitions of critical buildings and social and cultural buildings.
  • For the purposes of the consequence table, lifelines are considered to be the following:
    • Transportation;
    • Water and wastewater; and
    • Power distribution.

These lifelines may include both networks and nodes. Unlike the built environment categories, the consequences are assessed beyond the hazard zone. This is due lifelines being a network and therefore when they are damaged they often have effects beyond the hazard zone.

  • Economic consequences are measured as a percentage of Regional GDP as opposed to an absolute monetary amount rather than a dollar amount as recommended in the Risk Management Standard (4360). This method is preferred as the value of dollar amounts change over time, and does not allow for different scales e.g. $1 million of loss in a small provincial town would have a greater consequence than $1 million of loss in a large city. If the data is available, the GDP of the territorial authority could be used instead of the Regional GDP. The economic category only considers the immediate economic impact and is derived using the following equation:
    • Regional GDP / ((Value of buildings damaged + (number of deaths x $3.77 million) + (number of injuries x $207,000)) / Regional GDP) x 100.

The monetary value of deaths and injuries will change with time. The value used in the formula is based on the values of deaths and injuries as a result of vehicle accidents in New Zealand (Ministry of Transport, 2012).

  • Deaths are an absolute number and any calculations undertaken to estimate the deaths should be rounded up when a fractional number of deaths is calculated. For example, if the calculations result in 7.1 deaths, this should be rounded up to 8.
  • The risk-based approach can be used for cumulative and cascading hazards. The District Plan Chapter example (link) provides further information on how the consequence table can be completed for cumulative and cascading natural hazards.

Limitations

  • Scalability – while the table works well at the spatial plan, regional policy statement or district plan policy level or for larger scale developments (brownfield and greenfield), it is more limited at the individual consent application. In this case, a precautionary approach should be applied if required.
  • As with all frameworks that require specialist knowledge input, the content of the table has been developed with the best available knowledge at the time. This should not be a reason for not utilising the information – rather, where there are uncertainties around information (refer to Assumptions above), the precautionary principle should be applied.

Uncertainties

  • The parameters within the table have been based upon best available expert knowledge and opinion at the time of development. These may change over time and use.

STEP 3: Evaluate likelihood of event

Assumptions

  • The likelihoods provided are accepted by key stakeholders.
  • The table is scaleable, in that it allows of the evaluation of multi hazards i.e. flooding, landslides, tsunami, fault rupture.

Limitations

  • Likelihoods are based on the best available knowledge at the time.

Uncertainties

  • Likelihoods of certain hazard events are based on the best understanding of the hazard at the time of the assessment being undertaken. With time and as the science and understanding of the hazard improves, there could be changes in the likelihood of the event.

STEP 4: Take a risk-based approach

Assumptions

  • The decision around categorising the levels of risk (i.e. 1-4 permitted, 5-9 controlled, etc) is undertaken with consultation and engagement with local communities and stakeholders.
  • Not all consent categories (i.e. permitted, controlled, discretionary, restricted discretionary, non- complying, prohibited) may be required.

Limitations

  • Decision making process is based on the best available knowledge at the time

Uncertainties

  • Individual’s levels of risk acceptance are different, so final consent categories may reflect this.
  • Political influence and decision makers understanding and motives.

STEP 5: Monitor and review

Assumptions

  • The process of monitoring and reviewing policy will be undertaken as part of the Resource Management Act process.
  • The monitor and review process will be resourced and any findings will be given due consideration.

Limitations

  • Need to have base line data to provide something to measure progress against.

Uncertainties

  • Process and quality of monitoring process.
  • Quality of base line data to allow for monitoring.

Reference

Ministry of Transport (2012). Social cost of road crashes and injuries June 2012 update. Wellington, Financial, Economic and Statistical Analysis Team, Ministry of Transport.