Assessing Lack of Evacuation Capacity

Evacuation failure modelling shall lay open the spatially differentiated deficiencies of existing evacuation infrastructures with respect to their role in providing sufficient facilities to safe citizens in due time in the course of a tsunami event. The assessment shall be able to locate evacuation bottlenecks and difficult-to-evacuate areas by taking into account the available evacuation time, shelter capacities, population density, and main evacuation routes. From such modelling time-dependent expected casualties can be calculated. A comprehensive evacuation failure modelling approach includes the following steps:

 Hazard assessment to define evacuation zones and assign potential safe areas.

 Assessing areas with deficiencies in timely evacuation (difficult-to-evacuate areas).

 Calculating amount of people having difficulties to timely evacuate thus representing the number of potential casualties.

VII.7.1 Methods

In case people have more - or as much – available time to evacuate than they currently need (aET>= cET), they are able to reach a safe place and rescue themselves. High risk areas are those where people do not have sufficient time to find a safe place. Thus, the lack of evacuation capacity is a crucial factor of mortality R&V during the occurrence of a tsunami event. In the following the methods for assessing and mapping spatially distributed evacuation failure risks will be shown. The method builds upon the logic that people’s evacuation capacity is a function of the relationship between “current Evacuation Time” (cET, time people need to find a safe place) and “available Evacuation Time” (aET, time people have to evacuate in due time). The methods represent a complex aggregation of the following calculation steps presented as follows.

 Calculation of Available Evacuation Time at each point within the evacuation zone o Evacuation speed calculation.

o Assessing distances to safe areas.

 Calculation of Current Evacuation Time at each point within the evacuation zone.

 Calculation of Aggregated Risk of Evacuation Failure at each point within the evacuation zone.

Calculation of Available Evacuation Time VII.7.1.1

The available Evacuation Time (aET) is the function of the Estimated Time of Arrival (ETA) – from which by concept the Tsunami warning dissemination Time (TwdT) and the Reaction Time (RT) of the population is subtracted. Since it is not possible to quantify TwdT and RT the only parameter calculated is the estimated minimum time of arrival of the tsunami (ETA) per scenario and for predefined coastal locations. For each tsunami scenario the median value for a rasta cell (50th percentile of ETA distribution at the respective location) is calculated (LIPI et al.

2011b).

Calculation of Current Evacuation Time VII.7.1.2

The quantification of location specific current evacuation time is based on an ArcGIS cost-distance algorithm (ESRI, 2001). The evacuation time provides information on the time someone needs from a certain location within the warning level specific evacuation zone to reach the area where people are able to evacuate to the nearest shelter in a certain time following the fastest path. Hence, the current evacuation time is calculated based on the identification of the distance (via best evacuation route) between a given point within a defined evacuation zone to the next safe area as well as the calculation of evacuation speed.

Thus, methods include identifying safe areas and calculating evacuation speeds. On the basis of the calculated evacuation speed and starting from each of the placed access points, the current evacuation time can be calculated for any spatial area of interest (defined cells in ArcGIS). The value of each cell represents the cost (in terms of time) necessary to go from there to the

“costless” shelter following the fastest available evacuation path (Figure 27). In the following the single assessment steps are presented.

Evacuation speed calculation

The evacuation speed is measured by introducing a cost surface model. It assumes that land cover, population density, slope, critical facility density, age and gender distribution determine the evacuation speed of people. The cost surface model consists of a regular two-dimensional grid where each cell value of an area of interest represents the cost to travel calculated and transformed into an evacuation speed value. The evacuation speed is calculated with the

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 Land use and topography (slope) alters the evacuee’s movement and speed (ADPC, 2007).

For each land use and slope class a new speed value for a walking person has been calculated.

 Density of critical facilities distribution such as schools and hospitals result in reduced response capabilities due to the presence of people needing special attention during an evacuation. Obviously physical and mental disabilities are limiting factors for individuals to cope with during a disaster. Within a buffer of 100 meter around these facilities a speed reduction of 50% is assumed to meet the situation during an evacuation.

 Population density distribution. In evacuation modelling studies, different group sizes on evacuation speed properties are accounted for. It is assumed that the larger the population density the larger the group size will slower the evacuation process (Klüpfel 2012). Studies about average evacuation walking speed show values in the range of 0.7 to 1.5 m/s (Klüpfel 2003). For the calculation of the evacuation speed an average speed of 1.2 m/s is used for a medium population density area.

 Age and gender distribution (demographic population index). In several studies it has been found that age and gender are factors contributing to different mortality due to differences in evacuation speed. This is because average walking and maximum running speeds are age and gender specific in the productive age, whereby gender does not make a difference for children and the elderly. A respective index has been calculated (LIPI et al. 2011b).

Assessing distances to safe areas

The distance an evacuee located in an evacuation zone has to overcome during evacuation depends on the location and carrying capacity of safe areas. Safe areas include options for vertical and horizontal evacuation. To calculate the distance from each “grid cell” in the evacuation area (both “warning” and “major warning”) to a respective safe area, two major

variables are relevant: (1) The location of suitable shelter access points to safe areas (horizontal and vertical); and (2) their carrying capacity (vertical evacuation).

 To locate and determine suitable shelter access points, potential sites have to be assessed by applying a bunch of criteria such as favourable land use/cover and topography (slope) conditions as well as a minimum space of 10 000 m² ensuring the temporary gathering of evacuees. For horizontal evacuation areas, the access points are identified along the border of the hazard zone (maximum inundation line) accessible through the street network; for vertical evacuation shelters (existing buildings) on the top of buildings. To identify buildings suitable for vertical evacuation, their vulnerability has been assessed. Only buildings fulfilling criteria such as structural stability, accessibility, and non-liquefaction were selected as suitable for evacuation.

 Whether a shelter for vertical evacuation is accessible for people within an evacuation zone also depends on the carrying capacity of vertical shelters. Existing and available buildings suitable for vertical evacuation can have different primary functions (hotels, governmental facilities, schools, etc.) and therefore available space for evacuation is varying. As illustrated in Figure 28 below, during an evacuation the area surrounding a tsunami evacuation building is defined by either Evacuation time (L1) or Capacity range (L2) constraints.

Figure 26: Evacuation time and building capacity as decisive evacuation constraints (Source: LIPI et al 2011)

Calculation of Aggregated Evacuation Failure VII.7.1.3

The aggregated risk calculation for both warning levels is composed of three information layers.

The spatially distributed evacuation failure as outlined above has been overlaid by location specific hazard probabilities and intensities, as well as population density distributions. The yielded large number of 14 risk classes were aggregated to six classes ranging from very low (dark green) to very high (red).

VII.7.2 Results

Map 7 represents the spatial distribution of “risk of evacuation failure” at a scale of 1: 25 000.

The map is a result of the calculation of people’s evacuation capabilities and considers both, horizontal and vertical evacuation opportunities. Areas where evacuation is likely to be successful, i.e. an evacuation building or area can be reached within the available time, are indicated as low risk areas (green). Areas where evacuation is likely to be impossible are indicated as high risk areas (dark red).All currently existing buildings suitable for evacuation and their capacities are shown on the map. The following criteria were applied to determine a location where additional shelters are required:

 The time people need from each point to find a safe place

 The hazard zone and the Estimated Time of Arrival (Median ETA)

 The degree of exposure

The red and orange areas indicate where shelter areas are lacking. Additionally, the amount of people per village requiring additional shelter is shown on the map (circles). The circle size depicts the amount of people exposed per village, while the colours in the circles show the proportion of exposed people who are able to evacuate within 50 minutes (light grey), the proportion of people who are able to evacuate within 90 minutes (striped), and the proportion of people who are not able to evacuate (dark grey).

Map 8: Risk of Evacuation Failure Map, Cilacap (Source: LIPI et al. 2011)

The map shows that especially the coastal zone has the greatest problem to be evacuated in due time, whereby the largest share of the number of people requiring more than 90 minutes to evacuate lives in the coastal city centre and far off in rural Cilacap. A more detailed evacuation capacity related assessment has been conducted by the “Last Mile” project (H.

Taubenböck et al. 2009), supported a dissertation of Neysa Setiadi with the title “Assessing People ́s Early Warning Response Capability to Inform Urban Planning Interventions to Reduce Vulnerability to Tsunamis” (Setiadi 2014). The utility of the results for elaborating, assessing, selecting, and implementing R&V-R-task specific measures are discussed in chapter VIII.3.5

VIII. Case Study Part 4 – The Utility of Risk and Vulnerability