Risk and vulnerability assessment of the build environment in a dynamic changing society

Transcription

1 Risk and vulnerability assessment of the build environment in a dynamic changing society Limnei Nie SINTEF Building and infrastructure, P.O.Box 124 Blindern, NO-0314 Oslo, Norway. linmei.nie@sintef.no Cecilie Flyen Oyen SINTEF Building and infrastructure, P.O.Box 124 Blindern, NO-0314 Oslo, Norway. cecilie.oyen@sintef.no Kyrre Groven Western Norway Research Institute, P.O.Box 163, NO-6851 Sogndal, Norway. kyrre.groven@vestfors k.no; Carlo Aall Western Norway Research Institute, P.O.Box 163, NO-6851 Sogndal, Norway. caa@vestforsk.no; Summary This paper presents an integrated methodology for risk and vulnerability assessment in the built environment. It takes the changes in climate and society such as changes in land use due to urbanization and growth of population, and the capacity of existing infrastructures into account. The methodology can be implemented at macro scale (e.g. at municipal level) with broad information and data but limited accuracy, and at micro scale (e.g. at local catchment level) that needs detailed data and information with fine time and spatial resolutions. An example of risk and vulnerability assessment regarding urban flooding illustrates the structure of macro analysis. Case studies from two different climate regions and geographical locations in Norway are introduced to demonstrate impacts of climate change on urban drainage systems and buildings. Results from the macro scale analysis should be able to provide a framework of potential risk and vulnerability and priority for adaptation. The detailed simulations and analyses can assist municipalities to identify the problems and solutions for mitigation. The presented research approach provides a possibility to combine the risk events in nature (e.g. climate change) and society and assess their impacts on the built urban environment, taking the relevant critical infrastructures into account. The visible and forecast consequences call for sustainable solutions for adaptation and mitigation. However it should be noticed that in addition to the uncertainties in climate scenarios and other risk and vulnerability events, results of assessment and simulations should be more concrete and site specific, which required for data with fine temporal and spatial resolutions at urban scale. More research efforts and resources should be added to these weakness aspects. Key words: buildings, climate change, urbanization, critical infrastructure, urban flooding, sustainable management 1. Introduction Like the global situations, climate change, growth of population and urbanization, aging infrastructure and buildings are among drivers for changes. These changes have brought significant challenge to the nature, in particular to the built environment. In Norway climate change has proved a trend of the more extreme weather events having been more frequently in the last decades and has also projected the changing trend in the future; meanwhile increasing in air temperature and sea level rise will affect almost all regions, though the impacts vary greatly from one region to another due to the geographical locations and other potential threats [1]. Secondly, urbanization has changed the urban surface features with increasing percentage of impervious area and decreasing soil infiltration, which has caused consequences induced by urban runoff quantity and quality problems. Thirdly, the existing buildings and infrastructures, typically the urban stormwater drainage systems and the public road systems (also major drainage during flooding) were designed based on the climate conditions and standards at the time of construction. The

2 building and construction materials are deteriorating, capacities of the major and the minor drainage systems become insufficient with regard to changed urban catchment features and the climate. When the external changes encounter with internal failures, consequences such as loss of lives, economic damage and damage on the nature and the built environment are inevitable. The challenges are therefore obvious - what to do with the urban infrastructures regarding the changed climate and urban environment? A recent completed KS project - Consequences of climate change for infrastructure owned by municipalities and counties, commissioned by the Norwegian Association of Local and Regional Authorities presents results of climate change scenarios, climate vulnerability, climate adaptation and barriers regarding municipal physical infrastructures at municipality level. Five Norwegian municipalities in different climate regions and geographical locations in Norway are selected for case studies [2]. The project concluded that global and local climate change have been very well developed, although uncertainty is a central issue in the debate on climate change and climate adaptation policy; the changing in society is however little developed, and the most important, the link between changes in climate and in society is missing. As a common need for municipalities, public and private sectors, more detailed studies of the changes in climate and society with fine temporal and spatial resolutions are required in order to make clear assessment of plausible consequences and capacities for adaptation. The concept and main goal behind our research is to provide methodology and examples to assess the joint risk and vulnerability within the build environment caused by the changes in climate and society, and investigate measures for adaptation and mitigation from municipal to local levels. This paper presents some initial outcomes of an on-going project BIVUAC (Buildings and Infrastructure vulnerability and adaptive capacity to climate change) financed by the Research Council of Norway. 2. Climate and climate change in Norway 2.1 Climate in Norway Norway is situated in northern Europe, ranges from altitude about 57 o N in the south to 71 o N in the north and longitude about 10 o 45 E. According to a statistics of monthly air temperature during , 13 of the 15 stations that distribute in 15 counties have cold period from 2 to 7 months. 9 stations have 5 or more cold months [3]. The climate in Norway is however not unique. Regions along the coast like Bergen have mild climate, whereas regions inland have cold humid climate. Therefore climate change scenarios vary very much from one region to another. Associated analysis must take the diversification and localization into account. 2.2 Climate change scenarios Norway is divided into six climate regions with regard to change in air temperature and 12 regions for change in precipitation. Scenarios for sea level rise and storm surge in 2050 and 2100 are projected for all municipalities based on the condition in Figure 1 presents examples of the change scenarios of air temperature and precipitation and Figure 2 for the sea level rise for municipalities of Bergen and Fredrikstad in Norway. The relevant information refers to the report [1]. In addition to the three basic climate variables, other variables that identified having effects on safety and efficiency of urban infrastructures are wind, snow accumulation and snow melt, runoff, groundwater level, frozen period and soil moisture, etc. Both of the basic change parameters and induced effects should be considered in the climate analyses.

3 Fig.1 Scenario 2050 of air temperature ( o C) and precipitation (%, relative change from to ) for cities of Bergen and Fredrikstad in Norway Fig.2 Sea level rise, scenario 2050 and 2100 (relative to year 2000) for cities of Bergen and Fredrikstad in Norway

4 3. Methodology and models The goal of the research is to develop an integrated approach for risk and vulnerability assessment on buildings and important infrastructures caused by climate change and other dynamic changes in the society and their adaptive capacities. The structure of the model is illustrated in Figure 3. The analyses for assessment, adaptation or mitigation are suggested to carry out at two scales at municipal to local catchment levels with regard to the requirements for information for strategy making and planning, and evaluation of concrete measures for adaptation or mitigation. Fig.3 Model for risk and vulnerability assessment and adaptation (Adopted from Groven et al. (2008) [4] ) 3.1 Definition of terms Critical infrastructure is a term used to describe assets that are essential for the functioning of a society and economy. Most commonly associated with the term are facilities for generation, transportation and distribution of electricity, gas and oil, food, water supply and wastewater drainage, telecommunication and public transportation, and facilities and agencies for financial, health and security service. The scope of critical infrastructure may vary depending on the focus of analysis. In our study we estimate the impacts of extreme weathers on urban drainage system and buildings. Vulnerability in a general view refers to the susceptibility of a person, group, society or system to physical or emotional injury or attack. In this study vulnerability is used to describe the physical weakness to increasing risk of urban flooding caused by the changes in climate, society and infrastructures. Risk is defined as the effect, whether positive or negative, of uncertainty on objectives [5]. It is estimated by the result of frequency or probability and consequences of an uncertain event. 3.1 Assessment of risk and vulnerability and adaptation at municipal level The analysis at this level is a risk management approach, i.e. risk identification, assessment, prioritization for adaptation and mitigation. At this stage it requires general information in wide scope for risk assessment. Fig. 4 introduces a hierarchy of risk and vulnerability assessment for flooding in cities. Meteorological extreme events and failures of the technical system (here it is the drainage system) are two main risk events. Functions of Social and Critical Infrastructures (SCIs) and influence of Other Vulnerable Factors (OVFs) such as community manageability to emergency and responses of individuals may affect the occurrence and consequence of a disastrous event.

5 Fig.4 Hierarchy of risk and vulnerability assessment regarding flooding in cities Methodology and software to estimate the risk and vulnerability has been developed, e.g. InfraRisk [6]. Case studies are carried out in Norway [7] [8]. Results from this level should be able to help municipality to identify the potential risk events in nature, failures in the technical systems, vulnerability in society and critical infrastructures, and provide information of risk levels and priority for adaptation and mitigation. Nie et al. concluded that it is of utmost importance to bring area planners and landscape architects into the stormwater runoff planning and handle storm runoff to be an integral part of the municipal area planning. Applying Sustainable Urban Drainage System (SUDS) measures (also called Low Impact Development (LID) measures or Best Management Practices (BMP)) should be enforced by the Plan and Building Law [9]. 3.2 Risk and vulnerability adaptation and mitigation at local level Based on a preliminary analysis at municipal level, priorities should be given to those events or scenarios that have higher risk. For detailed simulation and analysis at local level numerical

6 models and detailed data with fine temporal and spatial resolutions are required. Results from this level should provide information of where the problems are and solutions to fix the problems. Applicable models vary from study areas of water and drainage systems, buildings, roads and transportation, and land uses etc. In this paper our assessment analyses focus on the impacts of climate change on urban drainage systems and the buildings. Software DHI-MOUSE hydrological and hydraulic model [10] and GIS technology are applied for generating model input data, simulations and result analyses. Climate change scenarios, types of land uses and density of population are included in the hydrological model. Two case studies are introduced in the next part of the paper. 4. Case study 4.1 Cities for case studies Two case studies in different geographical and climate regions are introduced: Bergen in west Norway with coastal and mild climate; Fredrikstad in south of Norway with warm inland climate. The two cities, like many other municipalities in Norway, have experienced climate change and the resulting consequences of combined sewer overflow (CSO) and flooding on urban surface and in the basements of the buildings [11]. 4.2 Ytre Sandviken in Bergen An urban catchment is situated in Ytre Sandviken in the city centre of Bergen. It covers the area of 180 ha from Sandviken in the north, through Vågen and the Fish market and drains to the fjord at Nordnes in the south. The catchment is highly urbanized and is served by combined sewer system. As such, CSO and flooding in basements due to intensive rains and high sea levels are common problems during extreme weathers. A sewer model was established using DHI-MOUSE software. It has 431 subcatchments, 1600 sewers and 1582 manholes and 33 overflow weirs. Simulations are run for design rains with return periods of 30 years for the present climate and artificial scenarios in 2030 and 2050 [12]. Consequences of sewer surcharge, CSO, buildings at risk of flooding are identified and presented in the Table 1. Table 1. Impacts of climate change on urban drainage system and buildings in Ytre Sandviken in Bergen Present Indicators of consequences 2002 Rainfall Sea level Rainfall Sea level ( 1 in 30 y) +20 % m +30 % +0.5 m Length of sewers under a pressure > 0.9 m No. of buildings at risk b CSO in one year (1 000 m 3 ) (2002 being the reference year) CSO in one month (1 000 m 3 ) ( being the reference month) (a). Lengths of surcharging sewers are identified while simulated water levels are 0.9 m over the tops of the sewers. (b). No. of buildings at risk of flooding were identified by a buffer of 10 m from the central line of surcharging sewers in condition (a).

7 According to the design standard for sewers in Norway, sewers must be installed at least 0.9 m below the basement floor in order to avoid basement flooding. We thus use the value as a criterion to estimate the buildings at risk of flooding. In case study of Bergen a buffer distance within 10 meters from sewers with a pressure level more than 0.9 meters is used to identify the number of buildings at risk of flooding. 4.3 Veumdal in Fredrikstad The Veumdal catchment is about 364 ha and served by separate and combined sewers. The separate sewer system covers an area of ha upstream, while combined sewer system for downstream area of ha, which is 37.6% of the total catchment. The sewage system stretches from Fredrikstad city centre in the south to the northern boundary of the city, which borders agricultural fields and forests. Elevation varies from 87 m at mountain areas down to 0.0 at the sea level. The catchment has outlet to River Veum but has no to the sea. A sewer model was calibrated based on the climate and measured runoff in Simulations were then carried out assuming precipitation increases 20% and 50% based on the temperature and precipitation in year 2004 to study the seasonal impacts of climate change on the urban drainage system and the buildings, i.e. sewer surcharge and combined sewer overflow (CSOs), flooding and affected buildings (Table 2). Table 2. Estimation of seasonal impacts of climate change on urban drainage system and buildings in Veumdal catchment, Fredrikstad (a). Lengths of surcharging sewers are identified when simulated water levels are over the tops of the sewers. (b). Lengths of surcharging sewers are identified while simulated water levels are 0.9 m over the tops of the sewers. (c). No. of buildings at risk of flooding are identified by a buffer of 20 m from the central line of surcharging sewers in condition (b). 5. Conclusions This paper presents an integrated approach to assess the risk and vulnerability caused by changes in the natural (e.g. climate) and the society. The authors suggest a two stage analysis at macro and micro scales. The assessment at macro scale is risk-based analysis process and it requires

8 data and information in a broad scope with less accuracy. The results from this level should provide information for making strategy and priority for more detailed analysis, adaptation and mitigation in municipalities. The detailed analysis should thus be followed and based on advanced models and requires for data with fine temporal and spatial resolutions. Results from the detailed analysis should be able to identify the problems and provide solutions to fix the problems or reduce the consequences. The paper presents examples to demonstrate how the approaches are applied at the two scales and the difference of climate change effects in the two case study municipalities of Bergen and Fredrikstad. Due to the limitation of one paper, it is difficult to demonstrate the diversification of geographical and climate impacts in Norway. Although methodology and software to estimate the risk and vulnerabilities have been developed, efforts should be made on estimation of the frequency or probability of the risk events and vulnerability and their dependency. Moreover, availability of meteorological and hydrological data with fine time and spatial resolutions at urban scale are extremely important in order to provide reliable and detailed results for assessment, adaptation or mitigation, but missing in most municipalities. More research efforts and resources should be added to these weakness aspects. 6. Reference [1] HANSSEN-BAUER, I. (ed.), Climate in Norway in 2100 Background materials to NOU climate adaptation (preliminary issue in Norwegian). June [2] AALL C. (ed.), Consequences of climate change for infrastructure owned by municipalities and counties, commissioned by the Norwegian Association of Local and Regional Authorities, final report. 31 January ISBN: [3] NIE L., Statistics of monthly air temperature during for counties in Norway. Technical memo, February 2011 [4] GROVEN, K., Klimasårbarhet i bustadsektoren - Lokal sårbarheitskartlegging og klimatilpassing. VF-report 1/2005. [5] ISO 31000:2009: Principles and Guidelines on Implementation of risk management. National Standards Authority of Ireland. [6] VATN, J., Description of software InfraRisk. Department of Production and Quality Engineering, Norwegian University of Science and Technology. December [7] TORGERSEN, H., How to adjust risk and vulnerability analysis for the counties of Trøndelag to the climate changes (MSc. Thesis). Department of Industrial Economics and Technology Management, Norwegian University of Science and Technology [8] NIE, L.M., Heilemann, K. Hafskjold, L.S., Sægrov, S., Johannessen, B.G., Adapting community to flood risk and vulnerability caused by climate change. Proceeding of International Conference of European and Global Communities combine forces on Flood Resilient Cities, Paris, France, th November [9] NIE, L.M., LINDHOLM, O., BRASKERUD, B.C., Urban flood management in a changing climate. J. VANN, Vol. 2, 2009: pp [10] DHI SOFTWARE, MOUSE Surface runoff and pipe flow models. User guide and reference manuals of DHI MOUSE, [11] LINDHOLM, O., SCHILLING, W., CRICHTON, D., Urban water management before the court: flooding in Fredrikstad, Norway. Journal of Water Law, 17: [12] MADSEN, A.B., Flood damage and discharge of pollution in the city of Bergen Analysis the effects of climate change. Dept. of Mathematical Science and Technology, Norwegian University of Life Science. June 2007.