Assessing Social Vulnerability to Coastal Hazards: A Case Study of Bandar Lampung City Coastal Area

Bandar Lampung City’s coastal area is highly susceptible to coastal hazards due to its location within the subduction zone of the Indo-Australian and Eurasian tectonic plates. Additionally, the presence of the Anak Krakatau volcano in the Sunda Strait further increases the vulnerability of the city’s coast to natural disasters. This study analyses the current social vulnerability in the coastal area of Bandar Lampung City. The aim is to provide a starting point for disaster management and policy planning in the city. To determine the level of social vulnerability in the coastal area of Bandar Lampung City, social vulnerability mapping is conducted by overlaying four indices: population, population density, sex ratio, and dependency ratio. The data indicates that there is significant variation in the level of social vulnerability among the coastal areas of Bandar Lampung City. Specifically, 8 out of 25 villages in the coastal area of Bandar Lampung City exhibit high levels of social vulnerability. The villages of Bumi Waras, Pesawahan, and Keteguhan have the highest levels of social vulnerability in the coastal area of Bandar Lampung City. As revealed by this study, the indicators of population size and dependency ratio have the most significant impact on the level of social vulnerability. These findings are expected to provide valuable input to stakeholders in their efforts to reduce social vulnerability in coastal areas.


Introduction
Coastal zones are areas where marine and terrestrial ecosystems meet and are affected by both marine and terrestrial changes [1].These areas are rich in natural resources and play important ecological roles.It is estimated that 50-70% of the world's population lives in coastal areas and relies on their resources [2].Bandar Lampung, located in Indonesia, is a city with a 27.01-kilometer coastline [3].Bandar Lampung City, as the capital of Lampung Province, plays a crucial and strategic role in meeting the needs of the surrounding area [27].The city's economic activities in the coastal area are primarily derived from seaport operations and commercial activities in the marine and fisheries sectors [4].
According to data from the National Disaster Management Agency, 32 out of 41 coastal cities in Indonesia are prone to flooding (including tides), 29 cities are vulnerable to tsunamis, and 15 cities are vulnerable to extreme waves [5].The Regional Disaster Management Agency has stated that the coastal area of Bandar Lampung City is vulnerable to damage from natural disasters due to its location in the subduction zone of the Indo-Australian and Eurasian plates [6].In addition, the presence of the Anak Krakatau volcano in the Sunda Strait and the Semangko fault, which extends from Aceh province to Lampung province, contribute to the susceptibility of the coast of Bandar Lampung City to coastal disasters [7].Coastal disaster risks can have significant socio-economic impacts on communities [30].Daily activities, particularly for fishermen, are hindered due to disrupted infrastructure and environmental conditions, rendering them unable to sail [31].Furthermore, coastal disaster risks can result in reduced incomes, loss of livelihoods, and changes in behavior [8,9].To anticipate these issues, a study on social vulnerability in coastal areas is required, particularly in Bandar Lampung City.
Social vulnerability is a manifestation of social fragility in an area that arises due to dangers, threats, and disasters that can disrupt social life and cause significant losses in areas with vulnerable social conditions [10,11].Therefore, it is crucial to consider the social vulnerability aspect when formulating disaster-based regional planning and development [24].This paper analyses the social vulnerability in the coastal area of Bandar Lampung City as a starting point for disaster management and policymaking.

Study Area
The study area comprises four sub-districts that directly border the coast of Bandar Lampung City: East Teluk Betung, South Teluk Betung, Bumi Waras, and Panjang (Figure 1).The combined population of these sub-districts is 249,777 (see Table 1).Bandar Lampung City's coastal area faces significant challenges, including high poverty rates and inadequate waste management.These issues have led to the emergence of slums and the underutilisation of space [12].According to Damai [13], conflicts over spatial use can arise due to various factors, such as environmental pollution caused by the growth of slum settlements and inadequate spatial planning to accommodate uncontrolled population growth.Bandar Lampung City has experienced natural phenomena that are symptoms of climate change in recent decades [26,29].This situation is concerning because it has been aggravated by these phenomena.

Variables and Indicators
The variable used to measure vulnerability was sourced from various studies and literature.To generate the social vulnerability level in the coastal area of Bandar Lampung City, social vulnerability mapping was performed using the overlay method.The calculation of social vulnerability in this study was based on indicators such as population, population density, sex ratio, and dependency ratio.The study supports these indicators with secondary data obtained from the Department of Population and Civil Registry of Bandar Lampung City, the Central Statistics Agency, and agencies in each coastal sub-district of Bandar Lampung City.The social vulnerability analysis was conducted in all villages and sub-districts of the coastal area.The indicators are classified into three categories: high, medium, and low, based on their respective values.The larger the population, the higher the vulnerability.Ulfa [14], Tyas [15], Tiyansyah [16], Chorunnisa & Giyarsih [17], Rahmat [18], Hizbaron et al [19] 2.
Population Density The denser the population, the higher the vulnerability.

Sex Ratio
The higher the number of women, the higher the vulnerability.

Dependency Ratio
The more older people and children in the population, the higher the vulnerability.
Intervals for each social vulnerability class are identified based on the lowest and highest scores for each indicator.The weights are derived from the results of the Analytical Hierarchy Process (AHP) (refer to Table 3).
Each indicator is divided into three classes: high, medium, and low.The determination of the population density criteria interval is obtained from the following formula: The sex ratio is the ratio of the male population to the female population, calculated using the following formula:

Population
Population is a crucial factor in disaster management as it provides a benchmark for the number of people exposed during a disaster [22].The population indicator value for social vulnerability is calculated as follows: According to the calculation results, the villages with the largest population are Bumi Waras village in the Bumi Waras sub-district with 16,210 residents, Keteguhan village in East Teluk Betung subdistrict with 15,508 residents, and Panjang Utara village in Panjang sub-district with 13,606 residents.The finding is consistent with Al Marfuah's statement [23] that Bumi Waras sub-district has the highest population among the four sub-districts in the coastal area of Bandar Lampung City.This high population can be attributed to factors such as increased birth and immigration rates, as well as factors such as emigration and death rates [23].

Population Density
Population density refers to the number of individuals residing in a given area [20].It is determined by the area and the number of inhabitants.In disaster studies, population density is closely linked to vulnerability to disasters.Areas with high population density are more likely to have higher levels of vulnerability than those with low population density [21].The value of the population density indicator for social vulnerability is calculated as follows: The calculation results reveal that Kangkung village in Bumi Waras sub-district has the highest population density with 48,470 people/km 2 , followed by Kota Karang village in East Teluk Betung subdistrict with 43,907 people/km 2 , and Teluk Betung village in South Teluk Betung sub-district with 25,011 people/km 2 .These villages have a higher population density due to their location in densely populated areas.The area's high population density is attributed to the numerous economic activities available, including trading in markets and shops.Furthermore, topographical factors contribute to the area's suitability for industrial activities.

Sex Ratio
The sex ratio is the ratio of males to females in a given area at a specific time [20].It is usually expressed as the number of males per 100 females.This information is necessary to determine the percentage of the female population residing in a particular area.The vulnerability of an area increases with the number of women, as it affects the area's ability to respond to disasters [14].The following table presents the calculation of sex ratio index values for all sub-districts and villages in the coastal area of Bandar Lampung City.The table above shows that Gunung Mas village in South Teluk Betung sub-district has the lowest sex ratio (95.16) in the Bandar Lampung City coastal area, indicating a larger female population than male.This suggests a higher social vulnerability for the village, making it more likely to have a higher population exposure in the event of a disaster.However, Ketapang Kuala village in Panjang sub-district has the highest sex ratio of 115.05, indicating a lower number of women than men and therefore a low level of social vulnerability.

Dependency Ratio
A high dependency ratio indicates the presence of many non-productive age groups, which are considered vulnerable.The vulnerability indicator increases with a high dependency ratio and decreases with a low dependency ratio.The table below illustrates how to calculate the dependency ratio indicator for social vulnerability.The social vulnerability of an area increases as the dependency ratio increases.The working-age population has a higher ability to move and evacuate independently, resulting in a higher vulnerability class for the non-working-age group in the event of a disaster [22].

Social Vulnerability Level
Once all the values for each indicator of social vulnerability have been obtained, the total social vulnerability can be calculated by adding up the values for each indicator.The total social vulnerability found in each village and sub-district in the coastal area of Bandar Lampung City is presented below.9 shows that Bumi Waras village in Bumi Waras sub-district has the highest social vulnerability value of 0.48, followed by Pesawahan village in South Teluk Betung sub-district with a value of 0.44, and Keteguhan village in East Teluk Betung sub-district with a value of 0.40.These villages have high social vulnerability due to their large populations and a high proportion of nonproductive age groups.
The research shows that population indicators and dependency ratios have the greatest impact on social vulnerability.Villages with high levels of social vulnerability tend to have a higher proportion of population and dependents compared to other villages, resulting in a higher total social vulnerability score.Agustri and Asbi [25] suggest that demographic variables, such as population, greatly contribute to determining the level of social vulnerability in Bandar Lampung City.Meanwhile, Wibisono and Asbi [3] assert that population density and dependency ratio are the variables that most influence social vulnerability in some urban villages in the coastal areas of Bandar Lampung City.The map below (Figure 2) shows the distribution of social vulnerability in the coastal area of Bandar Lampung City.

Figure 2. Distribution of Social Vulnerability Levels in Coastal Areas of Bandar Lampung City
Figure 2 shows a significant difference in the distribution of social vulnerability in the coastal areas of Bandar Lampung City.Measures are required to address social vulnerability differences in the coastal areas of Bandar Lampung City.Ilmi, Asbi & Syam [28] argues that Bandar Lampung City needs to strengthen its adaptive capacity to cope with natural disasters, as mitigation efforts alone may not be sufficient from a disaster management perspective.The social vulnerability analysis conducted in the coastal area of Bandar Lampung City revealed high vulnerability values in the variables of population size and dependency ratio.This indicates a need for improved planning and management of coastal areas in Bandar Lampung City, particularly in addressing social vulnerabilities related to large populations and vulnerable groups (women, the older people, children, and people with disabilities).Therefore, in the context of disaster management, governments should prioritise areas with high populations and pay special attention to vulnerable groups.

Conclusion
The social vulnerability level in the coastal area of Bandar Lampung City varies significantly.Out of the 25 villages located in this area, eight have a high level of social vulnerability.Bumi Waras, Pesawahan, and Keteguhan are the villages with the highest social vulnerability value in the coastal area of Bandar Lampung City.According to the social vulnerability analysis results, indicators of population size and dependency ratio have the greatest influence on social vulnerability.The analysis highlights the need to improve planning and management of coastal areas in Bandar Lampung City, particularly in addressing social vulnerability related to population numbers and vulnerable groups in the face of disasters.Therefore, the government should pay more attention to high population areas, as well as vulnerable groups such as children, women, and the older people.

Figure 1 .
Figure 1.The Coastal Area of Bandar Lampung City and Its Location in Lampung Province, Indonesia

4 .
SR: sex ratio Pm : total of male population Pf : total of female populationEach indicator is divided into three classes: high, medium, and low.The determination of the sex ratio criteria interval is obtained from the following formula: Dependency Ratio.The dependency ratio is a comparison between the non-productive age population (under 15 years and above 65 years) and the productive age population (15-64 years), which describes the size of the dependents of the productive population for the non-productive population.The dependency ratio is calculated according to the following formula: P0-14 : total population age 0-14 years P15-64 : total population age 15-64 years P>65 : total population age >65 years Each indicator is divided into three classes: high, medium, and low.The determination of the dependency ratio criteria interval is obtained from the following formula:  =  −   Nmax : maximum value Nmin : minimum value n : class totals A high proportion of population, children, and older people indicate relatively low physical capacity, as they are dependent on the working-age population and tend to have limited mobility in the face of natural disasters.The assessment of social vulnerability is influenced by the indicators that have been mentioned.Each indicator has a different effect on total social vulnerability.The total score of social vulnerability in Bandar Lampung City coastal area is calculated according to the formula: Social Vulnerability = {0.37 (Population) + 0.09 (Population Density) + 0.22 (Sex Ratio) + 0.33 (Dependency Ratio)}

.
Sub-district Population of Bandar Lampung City Coastal Area

Table 2 .
Table 2 displays the social vulnerability indicators used.Social Vulnerability Indicators

Table 3 .
Social Vulnerability Weighting Results Based on the Analytical Hierarchy Process (AHP) [15]Social Vulnerability AssessmentSocial vulnerability is assessed by scoring each indicator according to the index criteria classification with specific scores and weights based on research papers and studies by Ulfa[14], Tyas[15], andTiyansyah [16].The assessment includes: 2.3.1.Population.Each indicator is divided into three levels: high, medium, and low.The determination of the population criterion interval is obtained from the following formula: 2.3.2.Population Density.Population density can be calculated using the following formula:

Table 4 .
Population Indicator Value

Table 5 .
Population Density Indicator Value

Table 6 .
Sex Ratio Indicator Value

Table 7 .
Dependency Ratio Indicator Value

Table 7
shows that East Teluk Betung and Bumi Waras sub-districts have the highest number of villages with high dependency ratios (4 villages each).In contrast, Panjang sub-district has the highest number of villages with low dependency ratios (4 villages), while South Teluk Betung sub-district has only one village with a high dependency ratio.Ketapang Kuala village in Panjang sub-district has the highest dependency ratio value, indicating that 100 residents of productive age support approximately 47 non-productive residents.In contrast, Kangkung village in Bumi Waras sub-district has the lowest dependency ratio value, indicating that 100 productive residents support approximately 32 non-productive residents.

Table 8 .
Determination of Total Value of Social Vulnerability 10 Table