Joanna Bac–Bronowicz
Institute of Geodesy and Geoinformatics
152-52 Sugo,
Takizawa, Iwate, Japan
[email protected]
Nobuyuki Maita
Graduate School of Software and Information Science,
Wroclaw University of Environmental and Life Sciences,
Poland.
E–mail: bac–[email protected]
Abstract
Esfandiar Zebardast1, PhD Associate Professor and Associate Dean for Research School of Urban and Regional Planning University of Tehran, Iran E-mail: [email protected] Mohammad Javad Koohsari Graduate Student Abstract Iran has experienced many destructive earthquakes in the last few decades. These earthquakes have resulted in the death of thousands of people and destruction of many villages and cities. Tehran City, the capital of Iran, with a current population of about 7.6 million is located at the foot of the southern slopes of the Alborz Mountain Range that form part of the Alps-Himalayan tectonic zone. This zone is one of high seismic potential with many peculiar active faults. Seismologists believe a strong earthquake will strike Tehran in the near future. While natural hazards will continue to occur, their capacity to become a disaster or merely a manageable event depends on many factors, including the magnitude of the hazard, the vulnerability of people and their communities, and the built environment. In this paper a methodology for assessing social vulnerability of individuals within households to risk from earthquake hazards is developed, using AHP and GIS, and applied in Zone 6 of Tehran City. The methodology starts by selecting social vulnerability indicators from the literature and then collects the relevant data needed for the analysis. AHP is used to identify how these indicators contribute to the vulnerability of a person within a household, and GIS is used to map the social vulnerability of the individuals in zone 6 of the Tehran City.
Introduction
Although considerable research attention has been paid to different components of biophysical vulnerability and the vulnerability of the built environment, our current knowledge about the social aspects of vulnerability is the least. Social vulnerabilities are largely ignored, because of the difficulty in quantifying them. This also explains why social losses are normally neglected in post-disaster cost/loss estimation reports (Cutter et al, 2003). The development of indicators of social vulnerability to natural hazards is a relatively small area of research (Dwyer et al, 2004) in developed countries, but not much research is done on social vulnerability and its contributing factors in developing countries. Since the geographic discrepancies in social vulnerability and its temporal and spatial changes in the future requires a different approach to preparedness, response, recovery, and mitigation in reducing vulnerability or improving local resilience to hazards (Cutter and Emrich, 2006:102), this paper attempts to contribute towards this gap in knowledge by developing and applying a model for social vulnerability assessment in Zone 6 of Tehran City.
Social vulnerability is partially the product of social inequalities (Cutter and Emrich, 2006:103). It includes place inequalities, those characteristics of communities and the built environment that contribute to the social vulnerability of places. The concept of measuring or assessing social vulnerability to natural hazards has been explored widely in emergency and disaster literature. However, research has largely focused on qualitative assessment methodologies rather than quantitative risk modeling. This may be due to the complex nature of people, social structures and culture, as well as the multi-disciplinary approach required to undertake such research. Although no single investigation into vulnerability indicators will provide a holistic and comprehensive answer, there are aspects of vulnerability that can be explored and represented through the development and application of quantitative vulnerability indicators (Dwyer et al, 2004). Indicators are used to assess processes or phenomena that are difficult to measure directly and this is the case with social vulnerability. The question is that is there a robust and consistent set of indicators for assessing social vulnerability?
Social vulnerability and indicators
Cutter et al have reviewed relevant literature and have summarized the major factors that influence the social vulnerability. They have identified the relevant factors, which include:
- Lack of access to resources;
- Limited access to political power and representation;
- Social capital; building stock and age;
- Frail and physically limited individuals;
- Type and density of infrastructure and lifelines.
Although there is a disagreement in the selection and use of specific indicators to represent these broader concepts. The generally accepted set of indicators is:
- Age, gender, race, and socioeconomic status.
- Characteristics depicting special needs populations or those that lack the normal social safety nets necessary in disaster recovery.
- The quality of human settlements (housing type and construction, infrastructure, and lifelines) and the built environment (Cutter et al, 2003:245).
Other studies have investigated methodologies of vulnerability indicator development within a comprehensive risk assessment. They include the Earthquake Disaster Risk Index (EDRI) developed and applied to several cities by Davidson (1997). In the calculation of the EDRI for each city, five main factors of hazard, exposure, vulnerability, external context, and emergency response and recovery planning are measured and the overall EDRI is computed. The Cities Project methodology for assessing relative community vulnerability was developed by Granger et al (1999). The Cities Project methodology for assessing community vulnerability involves the development of indicators that contribute to an overall ‘relative risk rank’. The indicators are grouped into five categories: setting, society, security, sustenance and shelter. Within these five themes, the indicators are a collection of physical, structural, economic and lifestyle factors chosen to measure a community’s vulnerability (Dwyer et al, 2004:12).
Measuring social vulnerability
For the purposes of this study, the criteria that are important for social vulnerability were extracted from the literature. Since we are to use AHP to calculate the relative importance, or weights of the factors and indicators chosen, they were classified in a hierarchical manner under the four broad categories of population, housing, socio-economic status and physical distance. In order to measure these criteria, they were further divided into several sub-criteria, as shown in Figure 1 that would represent them:
Population:
- Age: Those over 65 and those under 14 years old were considered more vulnerable.
- Gender: Females were considered more vulnerable than males.
- Average House Occupancy: Larger households were considered more vulnerable than smaller households.
Housing:
- Housing Quality: Less durable housing units are considered to be more vulnerable.
- Housing density: Densely populated housing units are considered to be more vulnerable.
Socio-economic status:
- Unemployment: Those who are unemployed, especially women are considered to be more vulnerable.
- Illiteracy: Those who are illiterate, especially women are considered to be more vulnerable.
Physical Distance:
- Adverse Facilities: Those who are in a close distance to such facilities as gasoline stations and danger-prone industrial establishments are considered to be more vulnerable.
- Facilitative Facilities: Those who are in a close distance to such facilities as open spaces, hospitals and fire stations are considered to be less vulnerable.
Using Analytic Hierarchy Process (AHP), the weights, or relative importance of factors and indicators contributing to social vulnerability was calculated. The results are shown as numbers inside the parentheses in Figure 1.
AHP is a widely used multi-criteria evaluation (Saaty, 1980) method. It assists the decision-makers in simplifying the decision problem by creating a hierarchy of decision criteria. The basic rationale of AHP is organized by the breaking down the problem into smaller constituent parts at different levels. Subsequent operations take place independently at different hierarchy levels with a smaller number of factors to take into account. The method is usually offered with the pair-wise comparison technique that simplifies preference ratings among decision criteria. In this study expert-choice software was used to calculate the relative importance of factors and indicators.
Each indicator was measured on a 0 to 10 ordinal scale based on their frequency and contribution to social vulnerability. For example, precarious housing condition was measured in the following manner:
- 0-20 percent in a census block: 2
- 20-30 percent in a census block: 4
- 30-40 percent in a census block: 6
- 40-50 percent in a census block: 8
- Above 50 percent in a census block: 10
For those census blocks that are located close to facilities that contribute to social vulnerability (such as gasoline stations and danger-prone industrial establishments), the following criteria were used:
- Within 0-300 meters distance: 10
- Within 300-600 meters distance: 7
- Within600-900 meters distance: 5
- For more than 900 meters distance: 2
Figure 1. Factors and indicators of social vulnerability
The Social Vulnerability Index (SVI) for each census block was calculated by multiplying the weight of each indicator in its obtained grade from the 0-10 ordinal scale assessment:
Wherein Wi is the weight of the iit indicator and the gj is the jth grade obtained by that indicator from the 0-10 ordinal scale assessment. GIS was used to calculate the SVI for all of the census blocks in the Zone 6.
The Study Area
Zone 6 together with Zone 12 composes the Central Business District (CBD) of Tehran City. Figure 2 shows the location of Zone 6 among the 22 Zones of Tehran City. Tehran City, with an average density of about 146 people per hectare in the built-up area, is a dense city by world standards (Bertaud, 2003:3). Tehran’s average administrative density is calculated to be about 110 people per hectare which is close to the average administrative density of Zone 6 (about 103 Persons per hectares).
Figure 2. The location of Zone 6 in Tehran City
Zone 6 with an area of 2,149 hectares, which is about 3.5% of the Tehran’s area, had a population of 237,292 people in 2006, which is about 3% of the Tehran’s population. About 60% of the area of the Zone 6 is built-up area. Of the total 59,112 buildings that exist in this Zone, about 41.3% is 1-3 storey buildings and the rest are more than 4 storey buildings. In 1996, about 26.4% of the buildings in this zone were 30 years old and more, whereas for the City of Tehran this figure is about 16%. Of the total 658 parks and open spaces of Tehran City, 27 parks and open spaces are located in this zone.
To examine the social vulnerability, socioeconomic data were collected for 1120 census blocks in Zone 6, our unit of analysis. Using the latest census, specific variables were collected that characterized the broader dimensions of social vulnerability identified in Figure 1. There was no data available for a few blocks which are identified in the figures as “No Data”.
Results and conclusion
The social vulnerability index (SVI) which is a relative measure of the overall social vulnerability for each census block, was calculated using the abovementioned methodology. To determine the most and least vulnerable of the census blocks, the SVI scores were mapped based on standard deviations from the mean into five categories ranging from –1.5 on the lower end to 1.5 on the upper end. Figure 3 shows the comparative vulnerability of census blocks in Zone 6.
Figure 3. The comparative social vulnerability of census blocks in Zone 6
The Social Vulnerability Index (SVI) ranges from 2.28 (low social vulnerability) to 8.91 (high social vulnerability) with mean vulnerability score of 1.46 (Std. Dev. of 5.47) for all Zone 6 census blocks. Census blocks with SVI scores greater than 1.5 standard deviations are labeled as most vulnerable. The vast majority of Zone 6 census blocks exhibit moderate levels of social vulnerability. With some notable exceptions, the most vulnerable census blocks appear in the south western part of the Zone 6 (Figure 3), census blocks with greater number of precarious housing, population density as well as higher percentage of women population. Census blocks labeled as the least vulnerable (more than –1.5 standard deviation from the mean) are mostly in northwestern parts of Zone 6.
Although there is no consensus about social vulnerability or its correlates, using the proposed model of vulnerability, we suggest that social vulnerability is a multidimensional concept that helps identify those characteristics and experiences of individuals and communities that enable them to respond to and recover from earthquake hazards. By using the social vulnerability index, mitigation efforts can be targeted at the most vulnerable groups or census blocks level. The development and integration of social, built environment, and natural hazard indicators and models will definitely improve our hazard assessments as well as mitigation efforts.
Acknowledgement:
The corresponding author wishes to thank the Office of the Vice-President for Research of the University of Tehran for financial support in the form of a research grant.
Bibliography:
- Bertaud, A. (2003) Tehran spatial structure: Constraints and Opportunities for Future Development, Ministry of Housing and Urban Development, Tehran.
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