4.5 Alternatives & scenarios

This use case belong to a series of use cases dealing with the analysis of changing risk.

In the last (and most complicated) use case of this series  users might want to analyze the combined effect of planning decisions they take now in relation to possible future scenarios. In other words, they would like to know which decision is the most "Change-proof". Here both the risk reduction alternatives as well as the possible future scenarios are defined, and for each combination hazard data is used in combination with elements-at-risk data for that particular situation.  A matrix is made of alternatives and future years under different scenarios, and you calculate losses and risk for multi-hazard for each combination. This is then used to determine the risk reduction in future years under different scenarios. Also a Cost- Benefit analysis is carried out but now the benefits change through time. Finally also a Multi-Criteria Evaluation can be performed to select the best alternative  

Keywords:

Alternatives; risk reduction; scenarios; future years; benefits; costs.

Introduction:

This part integrates the previous components. It will allow you to analyze which risk reduction alternative is the best change-proof. The analysis follows the following steps:

• Analyse the changes in risk for risk reduction alternatives for the different scenarios in a number of future years (2020, 2030 and 2040);
• Calculate annualized risk for each combination of risk reduction alternative and future year;
• Calculate annualized risk reduction (benefit) for each combination of risk reduction alternative and future year by subtracting the annualized risk with and without the risk reduction alternative;
• Use these different values for annualized risk reduction (benefits) in a cost-benefit analysis that compares risk reduction alternatives by taking inot account their behaviour under different possible future scenarios;
• Determine the most "change proof" risk reduction alternative;

 Flowchart:

The following animation gives an overview of the data that is used in this use case. The table below shows the combination of possible future scenarios, future reference years, and risk reduction alternatives. You can click on any part of the table to move through the presentation. 

Analysis steps:

Step 1: Loss analysis

• Adapt the script Loss_input and add the specific combinations of scenarios, alternatives and future years that you want to analyse.
• The table on the next page shows all the loss combinations that should be calculated for scenario 1 in order to be able to calculate the multi-hazard  risk. So for each combination of scenario, future year and alternative we have loss for three hazard types (floods, landslides and debrisflow) and each of these for three return periods (20 , 50 and 100 years). For scenario 2 this would look similarly.
• For scenario 3 the losses are basically the same as for scenario 1, because we are using the same land use scenario, and the same hazard maps. Only the frequency of the hazard events will differ, but this has not effect on the individual losses, but only on the risk
• The Loss_input script might need many lines, with different combinations of scenario, year, alternative, hazard type and return period. You can use a text editor to copy and past, and find&replace text easier.
• Once the Loss_input script is completed, run it. It will take a considerable amount of time, so a coffee break might be useful
• After completion it might be good to copy the result file: Result_LP to another directory as a back-up. 

The table below shows all combinations for scenario S1 , the no risk reduction situation, and the three risk reduction alternatives, for 4 future years. For each combination there are 3 loss maps for flooding (for 20, 50 and 100 year return period), 4 for debrisflows and 3 for landslides