VII. Case Study Part 3 - Empirical Research; Methods and Results
VII.5 Assessing Lack of Capacity to Access Timely Warnings
Once a tsunami warning has been issued by the national warning centre, a fundamental question arises, namely: Do tsunami exposed people receive the warning issued? Some might, some not, some too late. In the face of the very limited evacuation time available and in case the local spatial conditions are unfavourable for ensuring timely evacuation, tsunami warnings have to reach hazard prone communities in due time. If not, large parts of the exposed communities might get trapped and risk mortality in the course of a tsunami event. Hence, the lack of access of communities and social groups to warnings is a vulnerability factor increasing the risk of mortality during a tsunami. Although the best strategy is to channel warnings through all kinds of different devices available in a country, it is still necessary to look closer at capacity gaps in the communities’ access to timely warnings in rural, urban as well as uninhabited areas, where people might work.
VII.5.1 Methods
Figure 17 presents the key steps for mapping the access of exposed populations to tsunami warnings.
Figure 17: Process of mapping access to tsunami warnings by the population
Criteria Selection VII.5.1.1
The access of communities to timely tsunami warnings at different places day and night is the function of the following criteria, which are evaluated in terms of their usefulness for assessment.
Table 11: Overview on the criteria selection process
Criteria Assessment
High Deploying outdoor mass notification infrastructure is the responsibility of local governments. Investments can quickly increase timely access to warnings. Thus, assessing current conditions provides useful information to develop
High R&V-R practitioners can use social profiles of access to indoor mass notification devices to understand better which devices shall be given prioritized support and where outdoor warning infrastructure is essential to be deployed. Furthermore, assessing households’ indoor mass notification devices yields very reliable information.
Reliability of the tools (e.g. R&V to blackouts due to earthquake).
Low The reliability of different tools is well known, a spatial assessment is not relevant.
Device usage patterns of households and individuals during day and night and at different places.
Low Device usage profiles are a very important factor for having access to timely warnings. However, fluctuations in usage patterns are high and for most devices usage
Criteria Assessment Relevance
Explanation
Informal notification / warning communication: community based warning, word of mouth.
Low Informal notification is a very important factor increasing the likelihood that people have access to warnings. But for R&V-R practitioners to increase the communities’
access to warnings, deploying infrastructure is relevant.
Assessing the distribution of indoor mass notification devices among households VII.5.1.2
Household survey data20 were collected in 2008 in three districts (Padang, 1000 households;
Cilacap, 500 households; Bali, 500 households). The survey included questions on whether the households / respondents possess a radio, a TV, and a mobile phone. Based on these data two indicators were calculated:
Single device availability: The share of households in a village possessing a radio, or a TV or a mobile phone (in %). This indicator shows how the distribution of different devices among households and villages is, and which are the most relevant to be used for timely warnings. The results of the descriptive analysis were aggregated at the village level (desa) as the reference unit for deriving relative values (%).
Device diversity: Share of households (%) in a village having none, one, two, or all three devices. This indicator allows for receiving a spatially and socially differentiated picture of the likelihood that warnings reach tsunami exposed households disseminated through indoor mass notification.
VII.5.1.2.1.1 Assessing the spatial coverage of outdoor warning infrastructures
Depending on the cultural identities in the case study areas, different outdoor mass notification systems were selected for mapping. For example, in Cilacap and Padang the capacity of mosques to disseminate warnings was chosen for assessment, especially because in these areas religious leaders, NGOs and the local government had already started a process of coupling mosques with the local warning system. Also sirens play a role in these regions, as a few are installed and allow assessment (except for Cilacap).
Two steps need to be followed for calculating coverage areas of mass warning systems:
(1) System’s inventory: Compiling GPS information of all the locations where mass alert loudspeakers are placed including any kind of mass notification system existing within the tsunami exposed area.
(2) Estimation of the area where notifications are disseminated through a loudspeaker audible for the exposed populations. The geometry applied for calculating siren and mosque loudspeaker spatial coverage is circles. For mapping them in the urban and rural environment in the three pilot areas the buffer function in ArcGIS9.3 was applied. Thereby, two criteria determine conceptually the size of the area covered21 by mosque loudspeakers, sirens or other forms of outdoor mass notification:
i. Average city noise: Sound level (measured in dB) at which a siren cannot be heard anymore: This is 80 dB (Federal Signal Corporation, 2005);
ii. Output level of the speaker: siren / mosque loudspeaker / any other system.
Siren coverage calculation
Estimations of the area where exposed populations can properly hear a specific siren are based on sound projection measurements published by the Federal Signal Corporation (2005). Figure 18 illustrates the maximum radius for sirens in an urban environment. The data reveals that sirens become ineffective at 80 dB (average surrounding noise level).
21 The term “area covered” relates to the area where not only sound can be noticed, but where messages for guidance can still be understood.
Figure 18: Sound projection for three sirens with different output power (Source: Federal Signal Corporation 2005)
Respectively, by using different siren output levels, three categories of siren coverage radius can be estimated and mapped:
100 dB siren output = 120 m coverage radius;
120 dB siren output = 480 m coverage radius;
130 dB siren output = 960 m coverage radius.
Mosque coverage calculation
If authorities regard mosques as a suitable warning dissemination system, mapping their coverage area is needed. Inventories of mosques exist already in many statistics. Also data on GPS exists in some areas and need to be compiled where missing. This is also true for measuring mosque loudspeakers’ output levels. Each mosque loudspeaker has different output levels, but these could not be assessed. Instead, a 150 m radius was used and mapped for each mosque surveyed using the Buffer technique in ArcGIS 9.3 explained above.
VII.5.1.2.1.2 Assessing Exposure: Merging night and day time population distribution The method to calculate population densities at day and night time is based on land use and population data as described in chapter VII.4.1. For access to warning infrastructure maps, night and day population densities were merged. This was done by comparing the population density data values at day and night for each land use polygons and selecting only the higher value as the basis for the day and night exposure mapping. This step is important because decisions on
night exposure levels but the highest levels throughout 24 hours. In order to derive an exposure information layer, hazard inundation distribution information needs to be overlaid with the population distribution data to derive population distribution information for specific hazard areas. For methods of hazard inundation modelling, please compare chapter VII.3.1. For this map, the calculated maximum inundation area is used as an example.
VII.5.2 Results
The results have been processed as a map (
Map 4) and tabular data (Table 12), taking the district of Cilacap as example.
Map 4 represents an image of the spatially distributed degree of access of the population to indoor and outdoor warning infrastructure. The map consists of three different information layers:
Layer 1 - Hazard zone: This is the area of focus of the assessment, indicated by the colour boundaries of the exposure information.
Layer 2 - Exposure information: people exposed per km2 at day- and night time) classified as high (red), moderate (yellow) and low (green).
Layer 3 - Information on existing warning infrastructure: Provides an overview about the current status of warning infrastructure distribution and accessibility by the population.
a) Area covered with outdoor mass notification devices:
• Grey circle: Coverage area of the mosque loudspeaker
• Red circle: Coverage area of the sirens (only Padang, Bali)
b) Access of households to indoor mass notification devices in selected villages
Bar chart (blue, yellow, grey): % of households in a village possessing a radio, a TV and a HP (indoor mass notification devices).
Pie chart (grey, white, red): % of households in a village possessing all three, two, or only one of the indoor mass notification devices.
Map 4: Access to warning, of selected communities in the district of Cilacap, Java
People’s access to outdoor warning devices VII.5.2.1
The map shows that since in Cilacap so far no sirens are installed and the majority of the population has a strong religious affiliation to Islam, mosques play a key role for outdoor mass warning. The results reveal that although mosques are in general quite well established in all populated areas, its current distribution pattern is not adequate to function as a hub for warning dissemination, considering the need for timely warnings to all population groups.
Looking at both, population densities in the tsunami inundation zone (major warning) and the location of mosques and their spatial warning dissemination capacity, hotspots of outdoor mass notification deficiencies can be identified. With respect to this, three observations can be made that allow concluding that rural areas and non-inhabited areas seem to have the largest problems in accessing timely warnings:
Urban areas show higher mosque densities than rural areas;
But also in urban areas the spatial warning dissemination capacity of mosques is not sufficient;
People’s access to indoor warning devices VII.5.2.2
Table 12 shows the results for the two types of information based on data collected from the household survey, measuring the populations’ access to indoor mass notifications. Generally speaking for all villages, the share of households / individuals having TV at home is higher compared to radios and mobile phone, whereby the latter’s availability is higher than that of radios. Very little households have no communication devices at all; to the contrary, the share of households possessing three devices is higher than of those having only two or even one device.
Access to devices in HH (%) Device diversity in HH (%)
Village radio TV Mobile No device 1 device 2 devices 3 devices
Tambakreja 53 79 60 0 19,5 26,8 53,7
Tegalkatilayu 46 76 60 3,7 13,4 40,2 42,7
Mertasinga 48 71 71 2,5 30,5 39 48
Karangkandiri 53 80 61 3,2 24,5 35,1 37,2
Adipala 68 68 47 0 16,9 33,7 48,2
Widarapayung Wetan 48 69 55 7,3 17 34,1 41,5
Table 12: Calculation of village level access to indoor mass notification devices in Cilacap
This map allows for better location of the differences between different villages. For example, in the city centre of Cilacap, more than 50% of the population possess three devices in their households, whereas in the far eastern rural village Widarapayungwetan only 40% do so and a share of 7.3% of the population do not have any access to indoor mass warnings. The utility of the results for elaborating, assessing, selecting, and implementing R&V-R-task specific measures is discussed in chapter VIII.3.3and VIII.3.1.