- The effect of the mitigation measures on the avalanche risk can be extract by comparison of risk scenario a) and c), and is in evidence for all three avalanches. - Risk can also be reduced by changes of the susceptibility of loss for building. In the 1980s, the introduction of regulations regarding avalanche pressure resistivity for new constructed buildings caused a strong decrease of risk scenario a), especially for the Gidisrinner avalanche. - Until the 1980s, the relation between scenario a) and b) gives information about the vulnerability due to the occuring avalanche pressure. Buildings in the run out zone of the Gidisrinner avalanche are highly endangered as a result of a high pressure. In the area of the Großtal avalanche more buildings are endangered but only a low damage degree is estimated. - In general, the initial risk situation in 1950 is exceed by the factor 2 for the Großtal avalanches and nearly reached by the Gidisrinner avalanche in spite of construction codes and mitigation measures. The actual risk of the Großtal avalanche is in 2000 higher than before the construction of mitigation measures, therefore the strong increase of the damage potential compensated already the risk reduction owing to the mitigation measures and the lowered vulnerability. Universitätstrasse 7 1010 Vienna Austria e-mail: margreth.keiler@univie.ac.at www.univie.ac.at/geographie Rennweg 1 6020 Innsbruck Austria e-mail: rudolf.sailer@uibk.ac.at http://bfw.ac.at Langasse 88 6460 Imst Austria e-mail: christian.weber@wlv-austria.at Grabenweg 3 6020 Innsbruck Austira e-mail: fuchs@alps-gmbh.com www.alp-s.at Innrain 52 6020 Innsbruck Austira e-mail: andreas.zischg@uibk.ac.at geowww.uibk.ac.at 2) Building values at risk The values of the buildings were calculated by using the average prices of insurance companies for new buildings (on a price level of the year 2002). The data required for this calculation (size and function of building, number of storeys) was recorded. The changing size of buildings was taken from construction plans or descriptions, and thus it was possible to trace the building back to their original size in 1950. For all steps of decades, the values calculated per building were combined with the location of the building in the GIS (Keiler, 2004). The development of the damage potential is shown in the results as possible maximum loss (PML). Building categories: 1 = lightweight construction 2 = mixed construction 3 = massive construction 4 = concrete reinforced construction 5 = reinforced construction Avalanche Risk Assessment - A Temporal Approach Margreth Keiler (1), Rudolf Sailer (2), Philipp Jörg (2), Christian Weber (3), Sven Fuchs (4), Andreas Zischg (5) and Siegfried Sauermoser (6) (1) Department of Geography and Regional Research, University of Vienna (2) Federal Research and Training Centre for Forests, Natural Hazards and Landscape (BFW), Department of Natural Hazards and Alpine Timberline, Innsbruck (3) Federal Service for Torrent, Erosion and Avalanche Control, District Office Imst and Landeck (4) alpS Centre for Natural Hazard Management, Innsbruck (5) Department of Geography, University of Innsbruck (6) Federal Service for Torrent, Erosion and Avalanche Control, Section Tyrol, Innsbruck Introduction Overview of the region Landeck and location of Galtür in the west of the state North Tyrol/ Austria. Source: Tirol Atlas Snow avalanches pose a threat to settlements and infrastructure in alpine environments. In the area of natural hazards, risk is defined as a function of the probability of occurrence and the corresponding extent of damage. Extent of damage is constituted by the two factors damage potential (value at risk) and vulnerability. R = p * dp * v R = risk p = probablitiy dp = damage potential (value at risk) v = vulnerability Since the mid-twentieth century, both of these factors changed over time and consequentially influenced the development of avalanche risk in the settlement. For a better understanding of risk influencing factors the changes in avalanche risk between 1950 and 2000 were quantified. The risk analysis regarding building was conducted in the municipality of Galtür. Results Conclusion For the risk analysis, regarding the desing event, different risk scenarios were calculated for each avalanche track to show the different developments of the factors ‘value at risk’, ‘vulnerability’ and the influence due to constructions of mitigation measures in the release area. Risk scenario a) shows the cumulative possible loss regarding the maximum extent of the avalanche if no mitigation measures would have been erected. Risk scenario b) points out the development of the possible maximum loss (PML) and without considering the influence of mitigation measures and vulnerability of the elements at risk. Risk scenario c) illustrates the actual change of the possible loss taking into account the change due to the construction of mitigation measures, value at risk and varying vulnerability. Gidisrinner avalanche: The possible loss computed for risk scenario a) and b) increased by the factor 5 between 1950 and 2000. In contrast to this rise, scenario c) shows after a high increase until the 1980s (by factor 12) a decrease as a result of the construction of avalanche fences and the introduction of regulation for buildings reducing the vulnerability. Großtal avalanche (western part): The highest increase took place regarding the PML by the factor 5. Risk scenario a) and c) show a nearly similar development, but the rise in possible loss is lower (factor 2) than for scenario b). In spite of the construction of mitigation measures in the late 1970s scenario c) rose slightly. Großtal avalanche (eastern part): The result of risk scenario b) illustrates the same increase like the other avalanche tracks. The scenario a) and scenario c) rose by a factor of three and two, respectively. Both Großtal-avalanches are characterised by an impact causing a lot of small damages on a high number of buildings which sum up the values of the possible losses. Methods 1) Avalanche Process For each of the three avalanche tracks (Gidisrinner avalanche, Großtal avalanche (western part), Großtal avalanche (eastern part)) a scenario of maximum extent and a scenario of the extent after the development of mitigation measures, both based on the design event with a reoccurrence interval of 150 years, were simulated using the model SAMOS ( Snow Avalanche Modeling and Simulation). SAMOS includes a coupled model to simulate the dense flow layer (two-dimensional model) the superposed powder snow layer (three-dimensional model) of a dry snow avalanche and computes information on pressure, velocity, density, flow and deposition depth (Sampl & Zwinger, 2004). 3) Vulnerability The vulnerability is defined as the degree of loss (0 = no loss, 1 = total loss) to given elements at risk within the endangered area by avalanches. The susceptibility of loss is a function of the avalanche pressure (expressed in kPa) and varies with the methods used for construction (building categories). For the risk analysis the building categories and specific regulations due to avalanche pressure resistivity were determined. Limiting Values: pu = damage level pui = specific damage level pai = detach limit poi = destruction level p = avalanche pressure Gidisrinner-avalanche: resulting pressure modeled with SAMOS, maximum exent References: Keiler, M. (2004): Development of the Damage Potential Resulting from Avalanche Risk in the Period 1950 - 2000, Case Study Galtür. Natural Hazards and Earth System Sciences 4 (2). p. 249-256. Sampl, P. & T. Zwinger (2004): Avalanche Simulation with SAMOS. Annals of Glaciology, 38. p. 393 - 398 Wilhelm, C. (1997): Wirtschaftlichkeit im Lawinenschutz. Mitteilungen des eidgenössischen instituts für Schnee- und Lawinenforschung 54. Davos Susceptibility of loss (Wilhelm, 1997) 1 .9 .8 .7 .5 .6 .4 .3 .2 .1 0 0 5 10 15 20 25 30 35 40 45 1 2 3 4 5 maximum loss optional avalanche pressure (kPa)