A spatiotemporal multi-hazard exposure assessment based on property data

S Fuchs,A Zischg,M Keiler

doi:10.5194/nhess-15-2127-2015

Abstract

Abstract. The paper presents a nation-wide spatially explicit object-based assessment of buildings and citizens exposed to natural hazards in Austria, including river flooding, torrential flooding, and snow avalanches. The assessment was based on two different data sets, (a) hazard information providing input to the exposure of elements at risk, and (b) information on the building stock combined from different spatial data available on the national level. Hazard information was compiled from two different sources. For torrential flooding and snow avalanches available local-scale hazard maps were used, and for river flooding the results of the countrywide flood modelling eHORA were available. Information on the building stock contained information on the location and size of each building, as well as on the building category and the construction period. Additional information related to the individual floors, such as their height and net area, main purpose and configuration, was included for each property. Moreover, this data set has an interface to the population register and allowed, therefore, for retrieving the number of primary residents for each building. With the exception of sacral buildings, an economic module was used to compute the monetary value of buildings using (a) the information of the building register such as building type, number of storeys and utilisation, and (b) regionally averaged construction costs. It is shown that the repeatedly stated assumption of increasing exposure due to continued population growth and related increase in assets has to be carefully evaluated by the local development of building stock. While some regions have shown a clearly above-average increase in assets, other regions were characterised by a below-average development. This mirrors the topography of the country, but also the different economic activities. While hotels and hostels are extraordinarily prone to torrential flooding, commercial buildings as well as buildings used for recreational purposes are considerably exposed to river flooding. Residential buildings have shown an average exposure, compared to the number of buildings of this type in the overall building stock. In sum, around 5 % of all buildings are exposed to torrential flooding, and around 9 % to river flooding, with around 1 % of the buildings stock being multi-exposed. The temporal assessment of exposure has shown considerable differences in the dynamics of exposure to different hazard categories in comparison to the overall property stock. In conclusion, the presented object-based assessment is an important and suitable tool for nation-wide exposure assessment and may be used in operational risk management.

Highlights

World-wide data on natural disasters suggest an increasing number of reported events, of people affected and economic losses, but – in the most-developed countries – a decreasing number of reported fatalities since around 1900 (e.g. CRED, 2014; Munich Re, 2014)
Since spatially explicit data on the dynamics of exposure remained fragmentary, data on the temporal dynamics of natural hazard events resulted in misleading conclusions with respect to the underlying causes and effects (Pielke Jr., 2007), and studies on dynamics in loss data may have over-emphasized the effects of climate change (Barredo, 2009)
298 248 buildings (93.5 % of exposed buildings and 12.4 % of the entire building stock in Austria) are exposed to one hazard type, and 20 778 buildings (6.5 % of exposed buildings and 0.9 % of the entire building stock in Austria) are exposed to more than one hazard type: 18 089 buildings are exposed to river and torrential flooding, 2595 to torrential flooding and snow avalanches, 568 to snow avalanches and river flooding, and 237 to river and torrential flooding as well as snow avalanches

Summary

Introduction

World-wide data on natural disasters suggest an increasing number of reported events, of people affected and economic losses, but – in the most-developed countries – a decreasing number of reported fatalities since around 1900 (e.g. CRED, 2014; Munich Re, 2014). Apart from hazard dynamics (the natural frequency and magnitude of events), decreasing dynamics in mountain hazard losses may result from (a) increased efforts into technical mitigation (Keiler et al, 2012), (b) an increased awareness of threats being considered in land-use planning (WöhrerAlge, 2013; Thaler, 2014), both leading to less exposure, and (c) a decline in vulnerability (Fuchs et al, 2007; Jongman et al, 2015) which will not be further considered . Since spatially explicit data on the dynamics of exposure remained fragmentary, data on the temporal dynamics of natural hazard events resulted in misleading conclusions with respect to the underlying causes and effects (Pielke Jr., 2007), and studies on dynamics in loss data may have over-emphasized the effects of climate change (Barredo, 2009)

Methods

Results

Discussion

Conclusion