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4 Landslide Loss and Risk Assessment An understanding of the economic and societal impacts of land- slides is essential for informed decisions that address the risks from landslides and other ground failure hazards. Documenta- tion of injuries and deaths, property damage, economic disruption, relief and repair costs, and environmental consequences is part of such an understanding. Undertaking risk assessments of prospective losses for failure-prone areas is an allied and equally important process. Loss and risk assessments are essential for · establishing a sound rationale for risk reduction programs based on documented economic and societal impacts; · evaluating the cost-effectiveness of proposed interventions for landslide-prone areas; · creating mechanisms for risk sharing involving the public and private sectors through insurance, special assessment districts, or other financial risk pooling; · partitioning responsibility for landslide-related cleanup, repair, and rehabilitation costs; and · understanding the noneconomic consequences of landslides events, especially to the environment (e.g., damage to critical watersheds). The terminology of loss and risk assessment can be confusing. The term loss assessment is generally used in reference to retrospective assess- ments of the economic and societal consequences of a given event, and more refined loss analyses go beyond an accounting of direct damages to 51
52 PARTNERSHIPS FOR REDUCING LANDSLIDE RISK consider the economic and societal consequences of the event. The term risk assessment is generally used in reference to systematic prospective analysis of the extent of a hazard, the exposure of people and property to that hazard, the likelihood of a damaging event, and the likely resultant economic and societal consequences of that event. As articulated in the National Research Council "red book" (NRC, 1983) on risk assessments, risk assessments are the foundation for making decisions about the best means for managing a particular risk. Risk assessments can involve quali- tative characterizations or more sophisticated quantitative calculations, and they can be based on scenarios describing individual events or proba- bilistic assessments across a series of potential events. 4.1 LOSS ASSESSMENT The need for and problems in obtaining usable assessments of eco- nomic and other impacts of disasters constitute a problem that has been recognized in a number of recent studies. The basic problem is articulated in an NRC report addressing loss estimation for natural disasters: "There is no widely accepted framework or formula for estimating the losses of natural disasters to the nation. Nor is any group or government agency responsible for providing such an estimate" (NRC, 1999, p. vii). This issue, as it relates to landslides, was recognized with the 1980 publication of a U.S. Geological Survey (USGS) Circular that documented the costs of selected landslide events and called for systematic collection of loss infor- mation (Fleming and Taylor, 1980; also see Schuster, 1996; Schuster and Highland, 2001~. Box 4.1 describes the conceptual and practical issues involved in undertaking systematic loss assessments. The proposed National Landslide Hazard Mitigation Strategy identi- fied the need for a ". . . framework for compiling and assessing a compre- hensive data base of losses from landslides and other ground failure hazards, which will help guide research, mapping, and mitigation activities nationwide" (Spiker and Gori, 2000, p. 15~. The Federal Emergency Man- agement Agency and the insurance industry are identified as prospective leaders for two activities. The first is an assessment of the current status of data on losses from landslides and other ground failures nationwide. The second is to establish and implement a national strategy for compilation, maintenance, and evaluation of data on the economic and environmental impacts of landslides and other ground failures. The proposed strategy designates federal and state entities as responsible for creating a "robust national landslide hazards information clearinghouse system," local and private entities as responsible for collecting and distributing needed information, and the academic community as responsible for developing and sharing information.
[~E LOSS ~~ R~K ~S=S~ENT ~3 Despite Me 1dent1Acat10n in We national strategy proposal of over entities as appropriately leading loss assessment activ1Ues' Me USES and Me Associabon of American State geologists (CASE) have already taken Me lead by est^Ushing a partnership to undertake a loss assessment pact protect (Davis ~ at.' 20037 Me USES provided Ending to Me ALSO for a trial program to determine annual losses attributable to landslides in seven states (results Tom Is pact program mere not livable at Me time
54 PARTNERSHIPS FOR REDUCING LANDSLIDE RISK of publication of this report). The committee commends the USGS and AASG for establishing this partnership and suggests that a series of such pilot projects will be necessary to determine optimum approaches to the collection and management of loss data that encompass both the economic and the social consequences of landslides. The committee endorses the USGS proposal for a "landslide loss information" clearinghouse to act as the focus for loss information (see section 5.3) and urges the USGS and state geological and other agencies to collaborate to ensure that appropri- ate protocols for data collection and storage are established as part of the National Spatial Data Infrastructure (OMB, 2002~. The committee further recommends creation of a Learning from Land- slides (LFL) program to constitute a focal point for documenting the losses and other detrimental effects caused by landslides. Such a program could be modeled after the existing Learning from Earthquakes program funded by the National Science Foundation and coordinated by the Earthquake Engineering Research Institute. This LFL program would fund reconnais- sance teams comprised of relevant specialists to examine and document notable landslide events and their impacts, including economic conse- quences (see section 6.3~. 4.2 RISK ASSESSMENT Risk assessments are the foundation for making decisions about the best means for managing a particular risk. The challenges of undertaking effective risk assessments include many of the issues associated with loss assessments, as well as others noted in Box 4.2. Figure 4.1 illustrates the role of risk assessment in guiding management of landslide risks, as pre- sented in guidelines developed by the Australian Geomechanics Society (AGS, 2000~. Risk assessments provide informed options for risk management. As shown in the upper half of Figure 4.1, risk assessments are prospective analyses of the extent of a hazard, the exposure of people and property to that hazard, the likelihood of a damaging event, and the likely resultant economic and societal consequences of that event. Risk assessments can involve qualitative characterizations or more sophisticated quantitative calculations. They can be based on scenarios describing individual events or probabilistic assessments across a series of potential events. Although a number of American researchers and practitioners have been leaders in the development of landslide risk assessments (e.g., Einstein, 1988, 1997; Wu et al., 1996; Roberds et al., 1997), the range of procedures and their role in decision making are in general poorly understood in American practice, and consequently the use of formalized risk analyses is limited.
LANDSLIDE LOSS AND RISK ASSESSMENT 55 A nationally coordinated approach to publicizing landslide risk assess- ments offers the opportunity for broader dissemination and understand- ing, particularly at the local level. Risk assessments are not just technical undertakings. As emphasized in an NRC report that analyzed risk (NRC, 1996), risk assessments can be important processes for informing relevant stakeholders about potential consequences and for gaining consensus about appropriate steps to address
56 RISK ESTIMATION RISK CALCULATION RISK = (LIKELIHOOD OF SLIDE)x(PROBABILITY OF SPATIAL IMPACT) x (TEMPORAL PROBABILITY) x (VULNERABILITY) x (ELEMENTS AT RISK) CONSIDERED FOR ALL HAZARDS | ___ (or RISKCONTPOL) PARTNERSHIPS FOR REDUCING LANDSLIDE RISK lISK ASSESSMENT | RISK EVALUATION COMPARE TO LEVELS OF TOLERABLE OR ACCEPTABLE RISK ASSESS PRIORITIES AND OPTIONS CLIENT / OWNER / REGULATOR TO DECIDE TO ACCEPT OR TREAT TECHNICAL SPECIALISTTO ADVISE SK ANALYSIS | l CONSEQUENCE ANALYSIS FREQUENCY ANALYSIS ELEMENTS AT RISK ESTIMATE FREQUENCY PROPERTY QUALITATIVE l ROAD & COMMUNICATIONS QUANTITATIVE SERVICES l PEOPLE HISTORIC PERFORMANCE l TRAVEL DISTANCE l TEMPORAL PROBABILITY e.g., vehicles, persons RELATIVE TO INITIATING EVENTS RAINFALL l V U LN E RA B I Ll TY CONSTRUCTION ACTIVITY l RELATIVE DAMAGE EARTHQUAKE l l PPOEAE LITY OF l N.IUPY / LOSS OF LIFE | | SERVICES FAILURE / MALFUNC ON l I SCOPE DEFINITION | ESTABLISH BRIEF, PROPOSED METHODOLOGY | ~ HAZARD I DENT'FICATION l I CLASSIFICATION OF LANDSLIDE e.g., slide, debris flow, rockfall EXTENT OF LANDSLIDE e.g., slide, debris flow, rockfall TRAVEL DISTANCE OF LANDSLIDE RATE OF MOVEMENT e.g., creep, slow, fast l · 1- I RISK TREATMENT 1 TREATMENT OPTIONS ACCEPT RISK AVOID RISK REDUCE LIKELIHOOD REDUCE CONSEQUENCES TRANSFER RISK TREATMENT PLAN DETAIL SELECTED OPTIONS IMPLEMENT PLAN | POLICY AND PLANNING I l 1 it: 1 1- 1 ~ 1 1 MONITOR AND REVIEW I , FEEDBACK RISK CHANGES MORE INFORMATION FURTHER STUDIES 1 - FIGURE 4.1 Schematic illustration of landslide risk assessment and risk manage- ment decision processes. SOURCE: Australian Geomechanics Society (AGS, 2000~.
LANDSLIDE LOSS AND RISK ASSESSMENT 57 potential harms. In this respect, an understanding of the risk posed by potential landslides is a central ingredient of determining appropriate risk management strategies to address that risk. An example of qualitative approaches to risk assessment is the use of a scoring system for rock fall hazards by the Oregon Department of Trans- portation (Wu et al., 1996~. Highway segments are evaluated for the likeli- hood of rock falls based on past frequency of rock falls, geological structure, and other considerations. The potential hazard is then considered along with potential for accidents (related to highway width and sight distance) to produce a rock hazard rating score. A number of other states have implemented similar approaches, and one role of a national strategy would be to ensure that all states have access to techniques and informa- tion that have been field-tested and refined. An example of state-of-the-art quantitative risk assessment proce- dures for landslide problems is their use in Hong Kong (Box 4.3), where there is a substantial ongoing investment in improving hillside stability (Ho et al., 2000~. Quantitative risk analysis has been applied to assess the cost of managing risk and the direct and indirect benefits that result, to optimize the allocations of available resources, and to identify areas of concern for improvement. A recent review of trial applications of quanti- tative risk assessment in Hong Kong (Lo, 2001) concluded that it can be a very valuable tool in landslide risk management. Although the proposed actions described above for documenting landslide losses and risks are important and necessary for understanding the consequences of landslides, they should be perceived as one compo- nent of a dual approach. Risk assessments, together with loss analyses, are essential for informed decisions about the management of landslide risks. The committee strongly recommends that a national strategy for landslide loss reduction establish and promote the use of sound risk analysis methods for understanding landslide risks and making informed loss reduction choices. Because the state of the art of such methods is evolving, further development of landslide risk assessment methods and documentation of their use are important components of a landslide research program. Technical assistance in the conduct of landslide risk analyses should be central features of educational and other outreach activities established as part of the national program.
58 PARTNERSHIPS FOR REDUCING LANDSLIDE RISK
LANDSLIDE LOSS AND RISK ASSESSMENT 59