Determination of the Damage Potential: a Contribution to the Analysis of Avalanche Risk
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Determination of the damage potential: a contribution to the analysis of avalanche risk M. Keiler, G. Meißl & J. Stötter Institute of Geography, University of Innsbruck, Austria Abstract Risk assessment involves analysing and evaluating both hazard and damage potential. While studies on natural hazard processes and the hazard potential are numerous, research on human aspects and the damage potential is rare. However, more attention needs to be drawn to the latter, as most parts of the Alps have undergone significant socio-economic changes since the mid-twentieth century. Methods and approaches which determine and assess the damage potential for risk analyses are still missing. This study presents a concept for an investigation and monetary assessment of buildings and mobile values as well as the estimation of the number of persons endangered by avalanches. The method is mainly based on digital data as well as statistical information. The results are presented corresponding to the existing hazard zones on a municipal level. Thus, buildings and mobile values as well as the number of persons of a region or district can be determined in a cost- and time-efficient way. Moreover the whole approach is incorporated in a Geographical Information System (GIS). The study is conducted and tested in the Paznaun Valley (Tyrol, Austria) and will be standardised for alpine regions. Keywords: natural hazards, avalanches, damage potential, risk assessment. 1 Introduction The United Nations declared the 1990s the International Decade for Natural Disasters Reduction (IDNDR). Its program focus was giving attention on increasing losses caused by natural hazards and promoting actions to reduce their impact. From a global perspective, alpine natural hazards like avalanches, debris flows, rock fall and landslides, cause only a small proportion of the total losses [1]. In the Alps, however, natural hazard processes affects society significantly, as economic and tourist activities as well as settlements share a spatially limited and intensively used area. The direct and indirect losses of the Risk Analysis IV, C. A. Brebbia (Editor) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-736-1 188 Risk Analysis IV avalanche winter 1999 represent an extreme example [2, 3]. In order to reduce the impact of natural hazards, the UNO called for two basic approaches, which are mitigation planning (coordinated with land-use planning) and response (event coping and recovery) [4]. Comprehensive mitigation planning includes a) determining the location and nature of the potential hazards, b) characterising the population and structures that are vulnerable to specific hazards (risk results from a) and b)), c) establishing standards for acceptable levels of risk, and d) adopting mitigation strategies based on an analysis of realistic costs and benefits [4]. In general, society is far from reaching these objectives at present. Austria belongs to the few countries which have had hazard zone maps for a few decades. The hazard zone maps are incorporated with building bans and codes in land-use planning [5]. An improvement of risk assessment is necessary, because the hazard zones are only identified by assessing the hazard potential. For the subsequent steps of risk calculation, definition of the acceptable risk and cost/benefit analysis few approaches and conceptual proposals [6, 7, 8] exist, yet standardised methods are still missing. There are hardly any approaches for determining the damage potential for the risk calculation. Data of persons and tangible assets (like buildings) is due to protection of data privacy not available, or needs to be collected in a time- and cost-intensive way. In this study, an approach to determine the damage potential in a cost- and time-efficient way is presented. The newly developed approach was built up on a detailed investigation in the municipality of Galtür [9]. Available digital data and statistical information, the monetary assessment of buildings and mobile values as well as the estimation of the number of persons endangered by avalanches served as a basis for the investigation. Moreover, the whole approach is incorporated in a Geographical Information System (GIS). The study is conducted in the Paznaun Valley (Tyrol, Austria). The valley is divided into the four administrative municipalities of Galtür, Ischgl, Kappl and See. These municipalities have undergone significant socio-economic changes from farming villages to tourist resorts since the mid-twentieth century [10]. Due to location, topography and political interests, winter tourism influences the structures of the municipalities more or less intensively. Seasonal fluctuation of damage potential (persons, mobile values) is pointed out by most of the approaches [7, 8], but only residents and immobile values are considered. Regarding increasing losses of tangible assets, the proportion of mobile values like passenger cars is rising. In this study, the fluctuation of damage potential caused by tourism is determined. The results of this generalised approach in the Paznaun Valley are outlined, followed by a critical comparison of the presented results with those of the detailed investigation in the municipality of Galtür [9]. 2 Methods 2.1 Buildings Digital data for the evaluation of buildings was provided by the Tyrolean state government, division spatial planning and statistics (TIRIS). Following data Risk Analysis IV, C. A. Brebbia (Editor) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-736-1 Risk Analysis IV 189 were available for the study: coloured orthophotos, as well as information on location of buildings and addresses. The digital data was incorporated in a GIS, updated by interpretation of orthophotos and intersected with the addresses. By means of analysing additional information, such as accommodation statistics and attributes of addresses, the functionality of buildings (inter alia residential building, hotel, guesthouses, public buildings, business) and the building height were derived. If no data was available, buildings were classified as residential buildings. The height of buildings was estimated using the average value according to the building function, which was recorded by the detailed investigation in the municipality of Galtür [9]. Based on the data attained and the calculated area of buildings by using GIS, the volume of each building was determined. In a subsequent step, the value of buildings was estimated with respect to the average prices of insurance companies for new buildings and the corresponding functionality of buildings. Buildings with special functions, like churches, petrol stations, ski lifts or sewage plants were not evaluated due to missing or not clearly definable assessing criteria. For this purpose, detailed analyses are necessary for each building. 2.2 Persons When determining the number of persons in the avalanche-prone areas, permanent (residents) and temporary (tourist) population were distinguished. The number of residents is derived from statistical data of households [11] and the average number of residents at the end of year (31.12.) from 2000 – 2002 [12] in each municipality. At the end of the year, the number of residents is higher than at the reference date of the census (15.05.). The manpower increases in the winter season due to intense winter tourism in the region and has to be considered in the statistic. The number of residents for each building was determined by using the number of flats in the building and the average size of a household. The potential number of tourists in the endangered buildings was calculated by using the official number of beds specified by local tourist board. The data represent values with maximum occupancy rate of beds assumed. 2.3 Passenger cars Collecting data on passenger cars is closely attached to the investigations of potentially present persons. For estimating the number of passenger cars per residents, the ratio between registered motor vehicle [13] and the number of residents in the district of Landeck in 2002 were statistically analysed [12]. The number of tourist passenger cars was calculated by employing information on the chosen means of transport and the number of passengers per tourist car. A questionnaire-based survey conducted in the municipality of Galtür and the results of a study on arrivals and departures of tourists [14] show that 95% of the tourists arrive by car. In addition, 3-4% uses private bus companies and 1-2% public transport in winter. Bed & breakfast businesses or small guesthouses register solely arrivals by private cars. Therefore, the number of beds is reduced Risk Analysis IV, C. A. Brebbia (Editor) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-736-1 190 Risk Analysis IV by 5% for hotels; in all other businesses the total number of beds is considered for the calculations. In a next step, the number of the potential tourist passenger cars was calculated applying the average number of passenger per car in leisure- time (2.34 persons) [15]. The value of the passenger cars was determined using the price of the most popular brand (Volkswagen) and the most sold type of car in Austria in 2002 [13]. 2.4 Spatial analysis All information on the damage potential was intersected with the hazard zones for avalanches via GIS in order to point out the spatial variations. The basis of hazard zone mapping in Austria is the forestry law of 1975 and the respective decree of 1976. The zones are identified by taking the intensity of a design event with a recurrence probability of 150 years as a basis [18]. In the red zone it has to be anticipated that buildings are destroyed and persons in buildings are at the risk of their lives; any building activity is forbidden. In the yellow zone, avalanches have an impact on the economic and individual use of the area and can damage buildings. When observing building codes, it is, however, unlikely that those buildings are destroyed and people in buildings endangered [5]. The official hazard zone map was provided by the Federal Service for Torrent, Erosion and Avalanche Control, District Office Imst and Landeck.