4.1 Introduction to the use cases on changing risk and planning

The overall aim of e use cases in this chapter is to evaluate possible changes in risk to different natural hazards, in an area along the coast of a small Caribbean island state.

These changes may be related to possible risk reduction measures, but also to possible future scenarios related to land use change, population change, and climate change, and  the effect of possible intervention alternatives on top of these possible future scenarios

Keywords:

risk; risk reduction; alternatives; engineering structures; ecological structures, relocation; possible future scenarios; GIS analysis. 

Before you start: Use case Location: Uses GIS data: Authors:
You can first read the procedure on this web-page before downloading the data-set and software and carry out the hands-on training exercises  The use cases in this chapter are related to a hypothetical situation on one of the small Caribbean islands

Yes, the uses cases are accompanied by GIS exercises that utlize the ILWIS GIS software

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Cees van Westen

 

Introduction:

Download the text of the exerciseThe data set is based on original data that was prepared for an EU FP7 project SAFELAND (http://www.safeland-fp7.eu/) by the University of Salerno, Italy. The following persons have developed the original hazard maps:  Leonardo Cascini, Settimio Ferlisi and Sabatino Cuomo. They also supplied the high resolution image, the DEM, building footprints, roads etc. The original hazard maps have been modified in order to reflect the situation for the various alternatives. The land parcel maps have all been generated by ourselves based on available high resolution images. The whole dataset was modified to make it a generic case study reflecting a situation in an island country.

We also would like to thank Anna Scolobig from IIASA for her work on the risk reduction alternatives (which we have taken as they were) the stakeholder involvement and the stakeholder roleplay exercise.

Hari Narasimhan (ETH) and Emile Dopheide are thanked for their input in the cost-benefit analysis.  Also we would like to thank Andrea Tripodi for his work in the development of the case study.  Luc Boerboom and Ziga Malek are thanked for their input in the thinking about possible future scenarios. Kaixi Zhang is thanked for her feedback on the risk calculation method.

 

 

 

 

 

 

Objectives:

The use cases in this chapter can be used in different ways (see also the flow chart below): 

    1. Analyzing the current level of risk. In this workflow the stakeholders (e.g. local authorities) are interested to know the current level of risk in their municipality. They request expert organizations to provide them with hazard maps, asset maps, and vulnerability information, and use this information in risk modelling. They use the results in order to carry out a risk evaluation. 
    1. Analyzing the best alternatives for risk reduction. In this workflow the stakeholders want to analyse the best risk reduction alternative, or combination of alternatives. They define the alternatives, and request the expert organizations to provide them with updated hazard maps, assets information and vulnerability information reflecting the consequences of these alternatives. Once these hazard and asset maps are available for the scenarios, the new risk level is analysed, and compared with the existing risk level to estimate the level of risk reduction. This is then evaluated against the costs (both in terms of finances as well as in terms of other constraints) and the best risk reduction scenario is selected.
    1. The evaluation of the consequences of scenarios to the risk levels. The scenarios are related to possible changes related to climate, land use change or population change due to global and regional changes, and which are only partially  under the control of the local planning organizations.  The systems will evaluated how these trends have an effect on the hazard and assets (again here the updated maps should be provided by expert organizations) and how these would translate into different risk levels.
    1. The evaluation how different risk reduction alternatives will lead to risk reduction under different future scenarios (trends of climate change, land use change and population change). This is the most complicated workflow in the SDSS, as it requires to calculate the present risk level, the effect of different risk reduction alternatives, and the overprinting of these on the  scenarios. For each of these combinations of alternatives & scenarios new hazard, assets and risk maps need to be made.
    1. The use of a Spatial Decision Support System (RiskChanges) that allows you to do any of the above types of analysis using a  web-based analysis system.

Flowchart:

Problems definition and specifications:

1. Analyzing the current level of risk.

This will be treated in detail in use case 4.2: Analyzing the current level of risk

The steps in the  flowchart above are described here in more detail.

1.1 Stakeholders

Central in the whole process are the stakeholders. The envisaged users of the system are organizations involved in spatial planning, planning of risk reduction measures, or emergency preparedness and response. They work in a country with a specific legislation and planning process (See: Methodology Book chapter 7) and I organizations that have different mandates. These could be subdivided into:

  • Government departments responsible for the construction, monitoring, maintenance and protection of critical infrastructure (e.g. the Ministry of Public Works). Their mandate is to:
      • Plan the (re)location of critical infrastructure (roads, buildings and other critical infrastructure)
      • Design guidelines for construction of roads and buildings in potentially dangerous areas
      • Design of structural and non-structural  mitigation measures against flooding and landslides
      • Design of non-structural mitigation measures (e.g. watershed management)
  • Physical planning departments responsible for the with the mandate to make land development plans at different scales. Their mandate is to:
      • Develop national physical development plans
      • Develop local development plans
      • Develop guidelines for building construction in flood and landslide prone areas
      • Evaluate relocation options for settlements in endangered areas
      • Develop zoning maps with relevant hazard information for building control
      • Provide relevant hazard and risk information for land subdivision.
  • National Emergency Management Organizations (NEMO, ODM, NaDMA) with the mandate to:
      • Design disaster response plans
      • Organize volunteers for disaster response planning
      • Develop and management Early Warning systems
      • Shelter planning and management.

1.2 Hazard modeling and elements-at-risk/vulnerability assessment

The government organizations are generally rather small in the small Caribbean states involved in the CHARIM project. They normally have a few persons capable of visualizing spatial data using GIS, but are not sufficiently capable of carrying out the actual spatial hazard and risk analysis required as the basis for their work. Therefore they will work with external consultants that will carry out this type of analysis for them, and they have to specify the exact Terms of Reference of the work of the consultants.

These consultants may work on different topics:

Hazard modeling. Consultants provide the relevant information related to flood and landslide hazard for the required scales of analysis

  • National scale (for the entire island) with output at a scale of 1:25.000-1:50.000 for the island countries and 1:250.000 for Belize
  • Local scale (for specific areas) with output at a scale of 1:5.000 to 1:10.000 for specific planning areas (such as settlement areas)
  • Site-investigation scale (1:1000) for specific problem sites.

Hazard modeling involves the following components:

  • Analysis of triggering events. As hydro-meteorological hazards such as flooding and landslides are mostly related to extreme rainfall events, the analysis of historical rainfall from raingauges is essential. Magnitude-frequency analysis is used to analyse the return periods of specific rainfall scenarios, for which the corresponding hazard scenarios will be analysed.
  • Hazard initiation assessment. This involves the analysis of the the locations where hydro-meteorological hazards are like to be initiated, and quantify them. For flooding this involves a hydrological analysis, where triggering rainfall is translated into discharge for a given return period. For landslides this relates to the analysis of the susceptibility of landslide initiation through spatial analysis.
  • Hazard runout assessment. This involves the modelling of the possible intensities (spatial distribution of the quantified impact of the hazard) for the return periods used in the initiation assessment. For flooding this would result in flood height/flow velocity maps for different return periods. For landslides this would result ion potential runout areas of landslides and debrisflows.

Elements-at-risk and vulnerability assessment.

This refers to:

  • Creation of spatial elements-at-risk databases related to buildings, and to critical infrastructure. This requires extensive GIS work related to the creation of the spatial elements from high resolution satellite images and available data;
  • The characterization of these elements in terms of their types (e.g. occupancy types and building types for buildings, road types);
  • The characterization of these elements in terms of their replacement costs in collaboration with the Departments of Statistics and Economy;
  • The characterization of the distribution of the population for different temporal scenarios (e.g. daytime and nighttime, or for normal periods and tourist periods)
  • The selection of appropriate vulnerability curves for the various types of elements-at-risk that will be used in the risk assessment
  • To carry out social vulnerability assessment using data from the national census in collaboration with the Department of Statistics.

Part of this work should be done by the government organizations themselves as they have the mandate to collect spatial information on the elements-at-risk. For instance the Public works Department should develop a spatial database of the roads including all relevant characteristics related to road type, culverts, bridges , drainage, road cuts and embankment fills, and slope stabilization works. The Department of Physical Planning, together with other relevant Departments is responsible for collecting and maintaining a national building database with the relevant characteristics of buildings. In the establishment of these databases external consultants may play an important role, however on the long run for the respective government organizations would have the mandate to maintain and update these databases.

More information:

Read more on hazard assessment methods in the three books:

1.3 Risk Analysis

The crucial stage in the evaluation of possible risk reduction strategies is the analysis of risk, which is defined as the probability of losses related to potentially hazardous phenomena. Risk assessment is the use of available information to estimate the risk to individuals or populations, property, or the environment, from hazards. Risk analysis generally contains the following steps: hazard identification, hazard assessment, elements at risk/exposure analysis, vulnerability assessment and risk estimation.

Also this type of work generally is not carried out by the government organizations themselves, but rather by consultants, that have the right expertise to carry out this type of analysis for one or more types of hazards, in combination with one or more types of elements-at risk.  This work is done at the appropriate scale related to the objectives of the stakeholders. The risk assessment can be subdivided into the following components:

  • Exposure analysis. In this analysis hazard scenarios worked out by the hazard assessment consultants for different return periods (e.g. once in 10 , 25, 50 and 100 years) are combined spatially with the elements-at-risk and the number of elements-at-risk exposed to a certain hazard intensity is calculated. Also for each element-at-risk the (maximum) intensity is calculated given a certain return period.
  • Vulnerability assessment. The results from the exposure analysis in terms of the maximum intensity per return period are then used in combination with vulnerability curves or matrices for the respective elements-at-risk types. Through the vulnerability curves a translation is made from the intensities of the hazard to the expected degree of loss for the elements at risk.
  • Risk assessment. The results from the vulnerability assessment are then used in combination with the quantification of the elements-at-risk to calculated the expected losses. In the case of economic losses, the replacements costs for the elements-at-risk are used, resulting in specific losses per return period. In the case of population losses the number of people are used in combination with the population vulnerability resulting from the vulnerability assessment. The resulting losses for different return periods are summed up for given administrative units and integrated for the different return periods to provide the average annual losses.  These are used as the basis for the risk evaluation and for the formulation of possible risk mitigation measures.

More information:

Read more on risk assessment methods in the three books:

1.4 Risk Evaluation

After analyzing the risk it is important to determine whether the risk is too high, and where the risk is too high. This is called the risk evaluation stage, and is the stage at which values and judgements enter the decision process, explicitly or implicitly, by including consideration of the importance of the estimated risks and the associated social, environmental, and economic consequences, in order to identify a range of alternatives for managing the risks.Important considerations in this respect are:

  • Risk perception among stakeholders. Risk perception is about how individuals, communities, or governments perceive/judge/evaluate/rank the level of risk, in relation to many factors described in Chapter 6 of the Methodology book.
  • Risk acceptability. Ana acceptable risk is a risk which the society or impacted individuals are prepared to accept. Actions to further reduce such risk are usually not required unless reasonably practicable measures are available at low cost in terms of money, time and effort. The definition of acceptability levels is a responsibility of the national or local government in a country. Risk acceptability depends on many factors, and differs from country to country. Therefore it is also not possible to simply export them to other countries. Risk acceptability levels are generally done on this basis of individual risk levels or societal risk levels (using so-called F-N curves), which are described in chapter 6 of the Methodology book. 
  • Risk communication. An important component in determining the risk perception is the communication between the stakeholders of the levels of risk. Do government organizations actively involve other stakeholders in the consultation process of the actual level of risk and the possible risk reduction measures? 

More information:

Read more on risk acceptability methods in the three books:

2. Analyzing the best planning alternative

This will be treated in detail in use case 4.3: Analyzing the best planning alternative

The steps in the  flowchart above are described here in more detail.

2.1 Defining possible planning alternatives

In this workflow the stakeholders want to analyze the best planning alternative, or combination of alternatives. They define the alternatives, and request the expert organizations to provide them with updated hazard maps, elements-at-risk information and vulnerability information reflecting the consequences of these scenarios. Once these hazard and asset maps are available for the scenarios, the new risk level is analyzed, and compared with the existing risk level to estimate the level of risk reduction. This is then evaluated against the costs (both in terms of finances as well as in terms of other constraints) and the best risk reduction scenario is selected. The planning of risk reduction measures (alternatives) involves:

  • Disaster response planning: focusing on analyzing the effect of certain hazard scenarios in terms of number of people, buildings and infrastructure affected. It can also be used as a basis for the design of early warning systems.
  • Planning of risk reduction measures, which can be engineering measures (such as dikes, check-dams, sediment catchment basins), but also non-structural measures such as relocation planning, strengthening/protection of existing buildings etc. 
  • Spatial planning, focusing on where and what types of activities are planned and preventing that future development areas are exposed to natural hazards. 

The methods for risk reduction planning can be subdivided into :

  • Structural measures refer to any physical construction to reduce or avoid possible impacts of hazards, which include engineering measures and construction of hazard-resistant and protective structures and infrastructure. The strategy is to modify or reduce the hazard.
  • Non-structural measures refer to policies, awareness, knowledge development, public commitment, and methods and operating practices, including participatory mechanisms and the provision of information, which can reduce risk and related impacts. With the aim of modifying the susceptibility of hazard damage and disruption and/or modifying the impact of hazards on individuals and the community.

The planning alternatives that are evaluated may be designed without considering the possible impact of hazard and risk, and in these situation the analysis is carried out to evaluate the impact of the different alternatives on the hazard and risk (will it increase or decrease). There are mostly different planning alternatives that can be formulated, and each of them may have advantages and disadvantages. The aim of this analysis to quantify their advantages and disadvantages in terms of hazard and risk reduction, and to evaluate these against the costs for implementation through a cost-benefit analysis. Also other criteria that cannot be quantified can be used in deciding the best alternative, using a multi-criteria evaluation.

For example for this use case we will select the following planning alternatives:

Planning Alternatives

Description

Codes used in the dataset

A0 (no risk reduction)

Do nothing

2014_A0_S0

A1 Engineering

Construction of engineering structures (e.g. flood walls, sotriage basins)

2014_A0_S1

A2 Ecological

Ecological disaster risk reduction measures (e.g. protective forest, bioengineering)

2014_A0_S2

A3 Relocation

Relocation of high risk elements-at-risk

2014_A0_S3

 

More information:

Read more on defining risk reduction measures in the three books:

2.1 Re-analyzing hazards and elements-at-risk

The implementation of certain structural or non-structural risk mitigation measures might lead to a modification of the hazard, exposure and vulnerability. Risk is a function of Hazard * vulnerability of exposed elements-at-risk * the quantification of the elements-at-risk. So there are several possibilities, that risk mitigation measures will influence:

  • The hazard. In terms of the probability (or return period) of specific hazard events, the spatial distribution of the hazard and the intensity of the hazards. For instance, the construction of a flood wall along a river may reduce the area that will be flooded. For certain lower return periods the flood wall may retain all flood water, and therefore the intensity (flood height) outside of the flood wall will become zero for these return periods. For more extreme events the flood intensity may become lower as a result of the flood wall. Therefore it is required to re-analyze the hazard given the implementation of the risk reduction measure.
  • The exposure of elements-at-risk. The number of elements-at-risk might change as a result of the risk mitigation measure, or planning alternative.  For instance if one of the alternatives involves relocation, the number of exposed elements-at-risk will decrease, whereas the hazard might stay the same. In other planning alternatives the effect of future development on the number of exposed elements-at-risk might also be evaluated.
  • The vulnerability of the elements-at-risk. The type of elements-at-risk might change as a result of implementing the planning alternative. For instance when retrofitting is considered, the number of elements-at-risk might be the same, as well as the hazard, but the vulnerability of these elements-at-risk might decrease, leading to a lower risk level. The same can be said for the implementation of an Early Warnign system. It will decrease the number of exposed people, but also their vulnerability, if they would move to shelters where they are better protected. 
  • The quantification of the elements-at-risk might change. This might refer to planning alternatives where the value of the exposed elements-at-risk changes, e.g. they could increase when more expensive housing is considered in a certain planning alternative. 

Therefore experts should evaluate together with the stakeholders what would be the effect of the proposed alternative on the hazard, elements-at-risk location and characteristics and the vulnerability. If needed new hazard modeling should be carried out, or new elements-at-risk maps should be made representing the new situation.

2.3 Analyze risk reduction

After re-analyzing the hazard, elements-at-risk and vulnerability for the situation after the implementation of the planning alternative, the next step is to analyze the resulting  level of risk, and compare this with the current risk level. The difference between the average annual losses before and after the implementation of the planning alternative, provides information on the risk reduction. This should be done for all the possible planning alternatives. The risk reduction should be done preferable both in terms of economic risk reduction (reduction in the average annual losses in monetary values) as well as in population risk reduction (reduction in the expected casualties or exposed people).  The analysis of risk requires a repetitive procedure which has to be carried out for each hazard scenarios (different hazard types and return periods) in combination with elements-at-risk types, and then also for each possible alternative. This requires the use of automated procedures using Geographic Information Systems.

2.4 Compare alternatives

Once the effect of the various planning alternatives has been analyzed, in terms of their risk reduction, the next step is to compare them and decide which of the alternatives would be the best to implement. This could be done through different methods:

  • Cost-benefit analysis. Here both the benefits and the costs can be quantified. The benefit of a risk reduction alternative is represented by its annual risk reduction in monetary values, which was calculated in the previous step (risk after implementation minus current risk). The costs for the planning alternative can be quantified as well in terms of their investment costs, maintenance costs, project life time etc. Cost-benefit analysis can be carried out by calculating relevant indicators, such as the Net Present Value, Internal Rate of Return or Cost-Benefit ratio.
  • Cost-effectiveness analysis. This is carried out when the costs can be quantified and compared, but the benefits in terms of risk reduction cannot be quantified in monetary values . This is the case for instance when population risk is calculated, as it is generally considered not ethical to represent human lives in monetary values. 
  • Multi-Criteria Evaluation. When both the costs and benefits cannot be quantified in monetary values, or when additional to cost-benefit or cost-effectiveness also other non-quantifiable indicators are used, a (spatial) multi- criteria evaluation is generally considered the best option. In this analysis also social , ecological , cultural and other criteria can be incorporated in the decision making process. 

The comparison of alternatives is generally carried in a process where the other stakeholders are also involved before a decision is taken on the optimal alternative that will be implemented. 

2.5 Final Decision and implementation

The last step of this workflow related to the selection of the optimal planning alternative in relation to the reduction of risk to hydro-meteorological hazards is the consultation with the various stakeholders involved. This includes public hearings with the population, private sector, non-governmental organizations, and various social network groups (e.g. communities, churches). The stakeholders have the opportunity to request adjustment to the proposed plan of action, and if these adjustments are considered valid, and substantial, a new round of evaluation might be needed if the change of expected hazard and risk impact is substantial. Once the plan is approval the procedures will start for the implementation of the plan. 

3. Analyzing possible future scenarios

This will be treated in detail in use case 4.4: Analyzing possible future scenarios

The steps in the  flowchart above are described here in more detail

3.1 Identification of possible future scenarios

The scenarios are related to possible changes related to climate, land use change or population change due to global and regional changes, and which are only partially  under the control of the local planning organizations.  The stakeholders might like to evaluate how these trends have an effect on the hazard and elements-at-risk and how these would translate into different risk levels. The possible future could be of the following types:

  • Climate change scenarios. In that case the stakeholders require the involvement of experts that would indicate which climate change scenarios would be evaluated and what would be the expected effects in terms of changes in frequency and magnitude of hydro-meteorological triggers would be expected, such as changes in sea-level and extreme precipitation;
  • Land use change scenarios. In this case the stakeholders require the involvement of experts that would indicate possible land use changes based on macro-economic and political developments which would be translated into local changes. For instance scenarios could be envisaged where an increase in tourism would be translated into possible future expansion of tourist facilities would be evaluated. The future land use scenarios would also involve possible changes in population which should also be taken into account. 
  • Future planning scenarios. In the national physical development plans also possible future developments will be outlined and priorities for development indicated which have implications for the spatial distribution of land use and population. 
  • Also combinations of these drivers might be considered.  

The possible future changes should be expressed for certain years in the future, for instance for 2020 and 2030 and are considered as a basis for long term planning.

For example in the use case that will be treated in this chapter the four possible future scenarios are:

 

Name

Land use change

Climate change

Scenario 1

Business as usual

Rapid growth without taking into account the risk information

No major change in climate expected

Scenario 2

Risk informed planning

Rapid growth that takes into account the risk information and extends the alternatives in the planning

No major change in climate expected

Scenario 3

Worst case

Rapid growth without taking into account the risk information

Climate change expected, leading to more frequent extreme events

Scenario 4

Most realistic

Rapid growth that takes into account the risk information and extends the alternatives in the planning

Climate change expected, leading to more frequent extreme events

 

3.2 Re-analyzing hazards and elements-at-risk for possible future scenarios

The possible future scenarios might lead to a modification of the hazard, exposure and vulnerability in certain future years from now. Therefore it is required to reanalyze:

  • The hazard. Possible future scenarios of climate change might lead to a change in the frequency and magnitude of triggering events for floods and landslides. Therefore a new magnitude-frequency analysis might be required, that take into account changing trends in frequencies of extreme events. The same hazard event that now has an average return period of 50 years, might have an average return period which is much smaller in a number of years from now. Also the intensities of the hazard might change for instance due to changes in land use which might affect the hazardous processes (e.g. deforestation scenarios). 
  • The exposure of elements-at-risk. The possible land use scenarios might lead to substantial changes in land use/land cover, which also has an important effect on the number of elements-at-risk within the various land use classes. The analysis of future changes in land use/land cover  is generally carried out based on land parcel maps, rather than on the basis of building footprints maps, as it is generally very difficult to translate the land use changes directly into possible locations of buildings. 

Therefore experts should evaluate together with the stakeholders what would be the effect of the possible future scenarios on the hazard, elements-at-risk location and characteristics and the vulnerability. If needed new hazard modelling should be carried out, or new elements-at-risk maps should be made representing the new situation. 

3.3 Analyze possible changes risk for possible future scenarios

After analyzing the hazard, elements-at-risk and vulnerability for (a)m future year(s) given certain possible future scenarios, the next step is to analyze the resulting  change in risk, and compare this with the current risk level. The difference between the current average annual losses and those in a future year under a given change scenario provides information for decision makers on the possible negative consequences of climate change and land use change scenarios. They can be used as  a basis for designing appropriate strategies for adaptation. The risk reduction should be done preferable both in terms of changes in economic risk (average annual losses in monetary values) as well as in population risk reduction (expected casualties or exposed people).  It is also important to incorporate the uncertainty levels in this type of analysis, thus providing a range of change rather than concrete values. 

3.4 Changing risk evaluation

After assessing the possible changes in risk that might result from a number of possible future scenarios related to climate change and land use change, stakeholders should analyze these changes carefully in terms of :

  • Spatial location of changes in risk. Some areas might be much more impacted by these possible future changes than others. Based on the outcomes of the analysis stakeholders could then prioritize certain areas for critical interventions. 
  • Critical sectors. Changes in risk could be analysed for different sectors of society, such as economy, agriculture, tourism, education, transportation etc.
  • Development of adaptation strategies. The analysis of the expected level of changes in risk and areas where an increase in risk is expected according to the possible scenarios, should lead to the formulation of adaptation strategies that aim to reduce these possible impacts through planning alternatives that could be implemented now.

 4. Analyzing planning alternatives under possible future scenarios

This will be treated in detail in use case 4.5.: Analyzing planning alternatives under possible future scenarios

The steps in the  flowchart above are described here in more detail

4.1 Selection of alternatives, scenarios and future years.

The evaluation how different risk reduction alternatives will lead to risk reduction under different future scenarios (trends of climate change, land use change and population change) is the most complicated workflow, as it requires to calculate the present risk level, the effect of different risk reduction alternatives, and the overprinting of these on the  scenarios. For each of these combinations of alternatives & scenarios new hazard, assets and risk maps need to be made. However, this type of analysis allows Stakeholders to make the most optimal "change proof" selection of planning alternatives. This type of analysis is entirely based on experts and consultants which should evaluate both the effects of the planning alternatives as well as the associated effects of possible future scenarios on hazard, vulnerability and risk.  Such type of analysis could be applied to specific critical areas, such as the capitals or important critical infrastructure. If we would put the combinations in a matrix the result would look like this:

Scenario: Possible Future trends

Alternative: risk reduction options

Now

2014

Future years

 2020

2030

2040

S0 (Without including any future trends)

A0 (no risk reduction)

2014_A0_S0

No future trends are taking into account, and all hazards, elements at risk and vulnerabilities are considered constant in future.

A1 Engineering

2014_A0_S1

A2 Ecological

2014_A0_S2

A3 Relocation

2014_A0_S3

S1 Business as usual

A0 (no risk reduction)

Does not exist: use existing situation

2020_A0_S1

2030_A0_S1

2040_A0_S1

A1 Engineering

2020_A1_S1

2030_A1_S1

2040_A1_S1

A2 Ecological

2020_A2_S1

2030_A2_S1

2040_A2_S1

A3 Relocation

2020_A3_S1

2030_A3_S1

2040_A3_S1

S2 Risk informed planning

A0 (no risk reduction)

Does not exist: use existing situation

2020_A0_S2

2030_A0_S2

2040_A0_S2

A1 Engineering

2020_A1_S2

2030_A1_S2

2040_A1_S2

A2 Ecological

2020_A2_S2

2030_A2_S2

2040_A2_S2

A3 Relocation

2020_A3_S2

2030_A3_S2

2040_A3_S2

S3 Worst case (Rapid growth +  climate change)

A0 (no risk reduction)

Does not exist: use existing situation

2020_A0_S3

2030_A0_S2

2040_A0_S3

A1 Engineering

2020_A1_S3

2030_A1_S3

2040_A1_S3

A2 Ecological

2020_A2_S3

2030_A2_S3

2040_A2_S3

A3 Relocation

2020_A3_S3

2030_A3_S3

2040_A3_S3

S4 Climate resilience (informed planning under climate change)

A0 (no risk reduction)

Does not exist: use existing situation

2020_A0_S4

2030_A0_S3

2040_A0_S4

A1 Engineering

2020_A1_S4

2030_A1_S3

2040_A1_S4

A2 Ecological

2020_A2_S4

2030_A2_S3

2040_A2_S4

A3 Relocation

2020_A3_S4

2030_A3_S3

2040_A3_S4

 

The table above indicates the combination of the four scenarios (S1,S2,S3,S4) and the 3 risk reduction alternatives (A1,A2,A3) in 3 future years (2020, 2030, 2040). In the case study we will use the coding of the files in a similar way: future_year_Alternative_Scenario. So for example:  LP_2020_A1_S2 refers to the land parcels for future year 2020 under alternative A1 (Engineering solutions) and for scenario S2 (risk informed planning).

4.2 Re-analyzing hazards and elements-at-risk for alternatives/scenarios

The combination of  the implementation of certain planning alternatives (structural or non-structural risk mitigation measures) in combination with certain possible future scenarios  will certainly lead to a modification of the hazard, exposure and vulnerability. This is why both the hazard maps and the elements-at-risk maps should be updated for each combination. 

  • The hazard. In terms of the probability (or return period) of specific hazard events, the spatial distribution of the hazard and the intensity of the hazards. For instance, the construction of a flood wall along a river may reduce the area that will be flooded. For certain lower return periods the flood wall may retain all flood water, and therefore the intensity (flood height) outside of the flood wall will become zero for these return periods. For more extreme events the flood intensity may become lower as a result of the flood wall. However the magnitude-frequency relation might change over time as a consequence of climate change, so if the flood wall is designed for a flood with a return period of 100 years, this might have reduced to a flood with a return period of 50 years under a possible climate change scenario. Therefore it is required to re-analyze the hazard given the implementation of the risk reduction measure and the possible future climate change/land use change scenario.
  • The exposure of elements-at-risk. The number of elements-at-risk might change as a result of the risk mitigation measure, or planning alternative, and also as a result of the possible future scenario.  For instance if one of the alternatives involves relocation, the number of exposed elements-at-risk will decrease, whereas the hazard might stay the same. However, under certain land use scenarios the pressure on the land might be so high that previously related areas might become occupied again. In other planning alternatives the effect of future development on the number of exposed elements-at-risk might also be evaluated.
  • The vulnerability of the elements-at-risk. The type of elements-at-risk might change as a result of the planning alternative and scenario combination. For instance when retrofitting is considered, the number of elements-at-risk might be the same, as well as the hazard, but the vulnerability of these elements-at-risk might decrease, leading to a lower risk level. The same can be said for the implementation of an Early Warnign system. It will decrease the number of exposed people, but also their vulnerability, if they would move to shelters where they are better protected. 
  • The quantification of the elements-at-risk might change. This might refer to planning alternatives and possible future scenarios where the value of the exposed elements-at-risk changes, e.g. they could increase when more expensive housing is considered in a certain planning alternative/scenario. 

Therefore experts should evaluate together with the stakeholders what would be the effect of the proposed alternatives and scenarios on the hazard, elements-at-risk location and characteristics and the vulnerability for a given future year. If needed new hazard modelling should be carried out, or new elements-at-risk maps should be made representing the new situation.

4.3 Analyze risk reduction for alternatives/scenarios

After re-analyzing the hazard, elements-at-risk and vulnerability for the specific combinations of planning alternative, possible future scenario and future year, the next step is to analyze the resulting  level of risk, and compare this with the current risk level. The difference between the average annual losses before and after the implementation of the planning alternative, provides information on the risk reduction. This should be done for all the possible planning alternatives/ scenario combinations. The risk reduction should be done preferable both in terms of economic risk reduction (reduction in the average annual losses in monetary values) as well as in population risk reduction (reduction in the expected casualties or exposed people).  The analysis of risk requires a repetitive procedure which has to be carried out for each hazard scenarios (different hazard types and return periods) in combination with elements-at-risk types, and then also for each possible alternative. This requires the use of automated procedures using Geographic Information Systems.

4.4 Compare alternatives under different scenarios

Once the effect of the various planning alternatives has been analyzed, under different future years and future scenarios, in terms of their risk reduction, the next step is to compare them and decide which of the alternatives would be the best to implement. In the cost-benefit analysis both the benefits and the costs can be quantified. The benefit of a risk reduction alternative is represented by its annual risk reduction in monetary values, which was calculated in the previous step (risk after implementation minus current risk). However,  whereas the benefit would remain constant in the analysis which was presented earlier under "Analyzing planning alternative", when we analyze the risk reduction of planning alternatives for different future years under possible change scenarios, the risk reduction might also change considerably over time. The costs for the planning alternative can be quantified as well in terms of their investment costs, maintenance costs, project life time etc. Cost-benefit analysis can be carried out by calculating relevant indicators, such as the Net Present Value, Internal Rate of Return or Cost-Benefit ratio. When we take into account possible future changes the cost-benefit ratios of the various alternatives might be quite different than if we consider no future changes, which might lead to the selection of another planning alternative that may be the most "change proof". 

4.5 Final Decision and implementation

The last step of this workflow related to the selection of the optimal planning alternative in relation to the reduction of risk to hydro-meteorological hazards is the consultation with the various stakeholders involved. This includes public hearings with the population, private sector, non-governmental organizations, and various social network groups (e.g. communities, churches). The stakeholders have the opportunity to request adjustment to the proposed plan of action, and if these adjustments are considered valid, and substantial, a new round of evaluation might be needed if the change of expected hazard and risk impact is substantial. Once the plan is approval the procedures will start for the implementation of the plan. 

Data requirements:

The uses cases in this chapter are all dealing with a hypothetical case study of a mountainous slope along the coast of a Caribbean island. It was decided to choose a hypothetical case because of the difficulty in getting the right data for any of the target countries in the the CHARIM project at this stage. This analysis requires local scale hazard intensity maps, detailed element-at-risk maps, vulnerability curves, risk reduction alternatives and future scenarios. Many of these data are still not available for the target countries. Nevertheless we hope that by following the use cases uin this chapter, users get a better idea of the procedure and can eventually also apply it in their onw country, once data is available.

  


Last update: 01 - 01 - 2015