RiskCity Exercise: Quantitative annual multi hazard risk assessment using risk curves

1. RiskCityExercise:Quantitative annual multi hazard risk assessment using risk curves Cees van Westen United Nations University – ITC School for Disaster Geo-Information Management International Institute for Geo-Information Science and Earth Observation (ITC) Enschede, The Netherlands E-mail: westen@itc.nl Associated Institute of the ISL 2004

2. Loss estimation methods • Qualitative: • Overlay of hazard footprints and elements at risk • Using a simple matrix approach • Using indicator analysis ( e.g. SMCE) • Using risk indices • Semi-Quantitative: • Scenario-based loss estimation • Probabilistic loss estimation • R = H * V * A • Quantitative (QRA) • Based on economic losses • Involving direct and indirect losses RISK = HAZARD * VULNERABILITY * AMOUNT ISL 2004

3. Quantitative Multi-Hazard Risk Assessment Procedure • Normalize all specific risk scenarios: • RISK = HAZARD * VULNERABILITY * AMOUNT • Calculate annual risk • Annual probability( for some we have to assume) • Vulnerability (for some we have to assume) • Amount (that is what we calculated already) ISL 2004

4. Seismic risk • Step 1: Defining earthquake scenario. • Step 2: Calculate the attenuation • Step 3: Calculate soil amplification • Step 4: Convert PGA to MMI • Step 5: Apply Vulnerability Functions for Building types • Step 6: Apply Vulnerability Functions for Infrastructure types • Step 7: Apply Vulnerability Functions for casualties • If additional information is available: • Step 8: Apply cost information to the buildings and combine with vulnerability to calculate losses for different return periods. • Step 9: Combine loss information for different return periods and calculate the risk by adding up the losses from these periods. • Step 10: Combine information and make summary ISL 2004

5. Seismic risk • Risk = Hazard * Vulnerability * Amount ISL 2004

6. 100 Discharge 25 10 5 Time Flood hazard modeling • Sobek: a two dimensional hydraulic model. • Input: • Digital Surface Model (Lidar) • Discharge data • Roughness data (landuse) • Output: • Flood depth • Flow velocity (Per time step) ISL 2004

7. Flood risk 5 years 50 years 5 years 50 years 10 years 100 years 10 years 100 years 25 years Mapping units 25 years Hazard polygons Buildings Affected ISL 2004

8. Flood risk • Risk = Hazard * Vulnerability * Amount ISL 2004

9. Flood risk • Risk = Hazard * Vulnerability * Amount ISL 2004

10. Qualitative risk assessment Qualitative_risk = Qualitative_risk [Susceptibility,Vulnerability] Susceptibility Two dimensional table Vulnerability ISL 2004

11. Calculating buildings in hazard zones Building map Susceptibility Calculates the number of houses in High, Moderate and Low susceptibility zones using a Building footprint map Cross 4426 buildings 9645 buildings 22019 buildings ISL 2004

12. Results using mapping units High Moderate Low 4426 buildings 9645 buildings 22019 buildings Quantitative risk assessment Only susceptibility Still to do Known now Risk = Hazard * Vulnerability * Amount How much percentage of the high, moderate and low hazard classes may be affected by landsides? In which period will these landslides occur? What is the vulnerability to landslides? Hazard = Spatial probability * Temporal probability The temporal probability that landslides may occur due to a triggering event. Here we will link the return period of the triggering event with the landslides that are caused by it. We have differentiated return periods of: 50, 100, 200, 300 and 400 years. The spatial probability that a particular area would be affected by landslides of the given temporal probability. This is calculated as the landslide density within the landslide susceptibility class. ISL 2004

13. Density in high Density inmoderate Density inlow From susceptibility to hazard Landslide_ID map If the indication of the high, moderate and low areas susceptibility is correct, different landslide events with different return periods will give different distributions of landslides in these classes. Million dollar information!!! The probability can be estimated by multiplying the temporal probability (1/return/period for annual probability) with the spatial probability (= what is the chance that 1 pixel is affected) Landslide related to different return periods Susceptibility Cross ISL 2004

14. Calculating hazard Assumption is that events with a larger return period will also trigger those landslides that would be triggered by events from smaller return periods Return periods Susceptibility classes ISL 2004

15. Calculating Vulnerability Estimating landslide vulnerability is very complex. It requites knowledge on the building types and on the expected landslide volumes and velocities. These are difficult to estimate. In many study landslide vulnerability of buildings is simply taken as 1, assuming complete destruction of the elements at risk. This would, however, in our case give too exaggerated values of risk. Simple assumption: The more buildings there are with 3 floors or higher, the lower will be the landslide vulnerability, as it becomes less likely that large buildings will be destroyed by landslides. Vuln:=iff(PerVacant=1,0,1-(Perc3floor+Percover3floor)) ISL 2004

16. Calculate losses Losses = Spatial Probability * Consequences Losses = Spatial P * V * A Loss_50_high:=0.0181*vuln*nr_b_high Loss_50_moderate:= 1.31199E-06*vuln*nr_b_moderate Loss_50_low:= 5.96345E-07*vuln*nr_b_low etc ISL 2004

17. Calculate losses Losses for a return period = sum of losses in high, moderate and low susceptibility areas What can you conclude when you compare the spatial probabilities and consequences for the high, moderate and low susceptibility classes ? ISL 2004

18. Calculate risk Period ISL 2004

19. Calculate total risk Total Risk = Area under curve Two methods: 1: Add trendline and integrate trendline 2: Use graphical method with triangles and rectangles ISL 2004

20. Combine hazard types ISL 2004

21. Combine annual risk ISL 2004

22. Thank you ISL 2004