Estimate of Informal Settlers at Risk from Storm Surges vs. Number of Fatalities in Tacloban City (Yolanda PH)

AMF Lagmay (a,b), KA Aracan (a), MJ Gonzales (a,c), J Alconis (a), I Picache (a), J Marmol (a), E dela Pena (a)

(a) Nationwide Operational Assessment of Hazards, Department of Science and Technology, Philippines
(b) National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City
(c) School of Urban and Regional Planning, University of the Philippines, Diliman, Quezon City

1. Introduction

On 8 November 2013, Typhoon Yolanda, international code name “HAIYAN”, barreled through the islands of central Philippines, with at least six instances of landfall in less than 20 hours . According to Masters (2013), the typhoon is considered the strongest typhoon on record with winds of 190-195 mph (~306-314 kph) at landfall. The Joint Typhoon Warning Center (JTWC) calculated its gustiness to 235 mph (~378 kph), the fourth strongest tropical cyclone in world history.

Tacloban City is a highly urbanized city in the northeastern part of Leyte island (Figure 1). Considered as the premier urban area in Eastern Visayas, it has been home to 221,174 persons and 45,478 households. It has been the center of commerce, education, and economic activities in Region VIII for decades.

Figure 1. Google Earth image of Tacloban City

Figure 1. Google Earth image of Tacloban City

As the 600 km-diameter Typhoon Yolanda crossed the Philippine archipelago, it brought widespread devastation over its path. Strong winds, heavy rainfall, and storm surges caused extreme loss of lives and widespread damage to property (Figure 2). Tacloban, one of the heaviest-hit cities suffered many casualties from storm surges with 2,646 dead and 701 missing (NDRRMC, 2014).

Figure 2: What is left of a coastal area in Tacloban after being hit by a storm surge after Typhoon Yolanda made landfall in Leyte (Photo by Bulilit Marquez, Associated Press)

Figure 2: What is left of a coastal area in Tacloban after being hit by a storm
surge after Typhoon Yolanda made landfall in Leyte (Photo by Bulilit Marquez,
Associated Press) 

2. Methodology

Figure 3. The four-step process employed in estimating exposure and risk of informal settlements

Figure 3. The four-step process employed in estimating exposure and risk of informal settlements

On November 7, 2013, the Storm Surge Hazard Mapping Team of Project NOAH produced a list of areas that will experience storm surge to be brought about by Typhoon Yolanda and the corresponding predicted surge height and estimated time when the maximum surge will be experienced. Tacloban ranked third on the list with 4.5 meters expected storm tide level. This list was generated based on simulations ran every 6 hours using Japan Meteorological Agency (JMA) model results using 11:00 No PST JMA forecast and WXTide results from 6 November – 10 November 2013.

Using this data, Flo-2D simulations were conducted on February 2014 upon availability of Digital Terrain Models generated from five-meter resolution Interferometric Synthetic Aperture Radar (IfSAR) data (Figure 7).

Figure 4. Brgy. 90, Tacloban City (Project NOAH Storm Surge Inundation)

Figure 4. Brgy. 90, Tacloban City (Project NOAH Storm Surge Inundation)

Storm surge inundation maps of these simulations were overlain on pre-disaster imagery from Google Earth, where the number of informal settlements was counted (Figure 4). Houses classified as an “informal settlement” in this study are those found in areas with a density of 0.03-0.04 houses per square meter and with roof dimensions from 20 up to 56 square meters.

Figure 5. Brgy. 90, Tacloban City (Post-Yolanda)

Figure 5. Brgy. 90, Tacloban City (Post-Yolanda)

Undamaged housing structures in the delineated areas on pre- (Figure 6) and post-disaster (Figure 5) imageries were then counted to come up with a total number of damaged houses in informal settlements. This number will be then multiplied to the average household size in Tacloban City based from the 2010 Census of Population of Housing conducted by the National Statistics Office.

Figure 6. Brgy. 90, Tacloban City (Pre-Yolanda)

Figure 6. Brgy. 90, Tacloban City (Pre-Yolanda)

3. Results and Discussion

According to the list derived by Project NOAH, a storm surge of 4.5 meters will likely hit the area on November 8, 2013 at around 11 oclock in the morning (Philippine Standard Time). A total of 688.51 hectares were deemed to be inundated by more than 1.5 meters (high) of storm surge while 531.73 19-hectares were inundated by storm surges 0.5 to 1.5 meters (moderate), and 12.97 hectares were inundated by less than 0.5 meters (low). A total of 1,233 hectares out of 10,544 hectares  of Tacloban City are at risk of storm surge. This represents 11.7 % of the area of the city. Twenty-six informal settlement areas in 24 barangays (villages) in Tacloban City were delineated.

Figure 7. Storm surge inundation map generated using IfSAR data

Figure 7. Storm surge inundation map generated using IfSAR data

Based from the manual counting of structures, 7,677 structures were believed to be damaged by the storm surge.

Multiplying this number from building occupancy, a minimum of 31,478 persons in informal settlements are exposed to storm surge hazard brought by Typhoon Yolanda.

If all deaths were to be assumed to be coming from informal settlements, then about 8.4 per cent of the exposed informal settlement population are believed to be dead (See table below).

table Yolanda estimate

This work is preliminary and a draft of an on-going study.

References

[1] NDRRMC, Sitrep no. 107 effects of typhoon yolanda (haiyan), national disaster and risk reduction and management council, Online (2013).

[2] J. Masters, ) super typhoon haiyan: Strongest landfalling tropical cyclone on record, Wunderground Blog.

[3] N. S. Office, Census of population and housing, Online (2010).

Leave a Reply

Your email address will not be published. Required fields are marked *

nineteen + 5 =