Some relevant issues in landslide risk assessment

Transcription

1 Geohazards Technical, Economical and Social Risk Evaluation A FIRST-ORDER SECONDMOMENT FRAMEWORK for PROBABILISTIC ESTIMATION of VULNERABILITY to LANDSLIDES

2 Some relevant issues in landslide risk assessment What are the sources of uncertainty in vulnerability to landslides? How can vulnerability be addressed accounting for uncertainties? How can uncertainty analysis help in achieving more rational decisionmaking? 2/13

3 Risk analysis for geohazards: reference definition RISK = HAZARD X ELEMENTS at RISK X VULNERABILITY 3/13

4 Vulnerability: social vs. technical; qualitative vs. quantitative Social vulnerability: the capacity of a society to cope with hazardous events Technical vulnerability: the degree of expected loss in a system in relation to a specific threat, from 0 (no loss) to 1 (total loss) Technical vulnerability is addressed herein in a quantitative sense 4/13

5 Uncertainties in vulnerability estimation Uncertainties in measured and derived parameters Uncertainties in models Uncertainties should not be ignored! Underestimation: dangerous Overestimation: uneconomic 5/13

6 Vulnerability: proposed quantitative definition VULNERABILITY = LANDSLIDE INTENSITY x EXPOSURE of VULNERABLE ELEMENTS 6/13

7 Categorisation of the built environment Different units should be used to quantify loss and risk for different categories Differerent components of the built environment behave differently to landslides Different approaches (e.g. models) are necessary to investigate the interaction between landslides and different components of the environment Examples of vulnerable categories: Structures; persons in structures; roads; persons in vehicles; environment; property; utlility lifelines; persons in open spaces 7/13

8 Exposure of vulnerable elements The proportion of each category of elements at risk expected to be affected by a reference landslide event (Lee & Jones 2004) Here: product of category-specific exposure factors E.g. structures: Structural-morphological characteristics, state of maintenance, strategic relevance E.g. persons: Age, capacity to anticipate and respond to a landslide Exposure can be temporally variable! 8/13

9 Landslide intensity A set of spatially distributed parameters describing the destructiveness of a landslide (Hungr 1997) No general quantitative parameter is available! Damaging aspects are essentially kinetic and spatial A composite (kinetic + spatial) intensity parameter is proposed 9/13

10 Influence of the scale of investigation Aleatory uncertainty is generally lower if vulnerability analysis is performed at site level rather than at regional level An additive model is proposed to estimate the global effect of the scale of investigation 10/13

11 FOSM approximation of vulnerability At category-level: Second-moment characterisation of exposure Second-moment characterisation of intensity FOSM approximation of vulnerability (product of random variates) 11/13

12 Importance of accounting for uncertainty: example output 1 Nominal value is greater in Area 2 2 Nominal + st.dev. is greater in Area 1! Area nominal value nominal + st.dev. This is an important information for planners, stakeholders, etc.! /13

13 Main closing remarks The interaction of landslides with the built environment is extremely complex and heterogeneous; this generates significant uncertainties in parameters and models for vulnerability assessment Main objective is the quantification uncertainties for rational decision-making It is hoped that better models and more data may be collected to reduce uncertainty associated with vulnerability assessment 13/13