Posted on November 22, 2013
Updated on January 7, 2014
AMF Lagmay, Project NOAH Storm Surge Team and WebGIS Team
Photo by Bulilit Marquez, Associated Press
On 8 November 2013, Typhoon Yolanda, international code name “HAIYAN”, made landfall in the central Philippine islands region. The typhoon is considered as one of the most powerful ever to make landfall in recorded history according to international weather agencies. 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. Tacloban, one of the heaviest-hit cities suffered many casualties from storm surges with 2,524 dead and 594 missing (NDRRMC, 2014).
In this study, we estimate the number of informal settlers living along coastal communities (Figure 1) vulnerable to hazards associated with super typhoon Yolanda.
Figure 1. Outline of an informal settlement along the coast in Brgy. 90, Tacloban City
We then compare this number with the fatalities reported by NDRRMC. The results provide a minimum estimate of Tacloban’s population in harm’s way of storm surges along a 23.7 km stretch of coastal land vis-a-vis the actual death count in the area.
Flo-2D simulations were conducted on 16 November 2013 using storm surge water levels predicted for the area by Project NOAH on 7 November 2013, over 10-m per pixel SAR-derived topography. Maps of these simulations were overlain on pre-disaster imagery, where the number of informal settlements were counted (Figure 2). 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. This study used informal settlements as reference to estimate the minimum number of people at risk from storm surges because they are easy to identify and count in airborne and satellite imagery.
Figure 2. Simulation of the storm surge with the outline of identified informal settlement areas. Yellow=up to 1 m; dark yellow=1-2 m; red= 2-3 m; purple 3-4 m; and 4 m and above.
A counter-check of the risk for these informal settlements was made by referring to post-disaster imagery and their impacts (Figure 3).
Figure 3. Photo of Brgy. 90, Tacloban City post-Yolanda
The number of informal settlements was then multiplied with a minimum number of three people per household to yield the minimum population of informal settlers at risk from the deadly storm surges of Yolanda.
Minimum estimate of informal settlers at risk from storm surges 31,478
Population of Tacloban City (NSO 2010) 221,174
Number of dead in Tacloban City according to NDRRMC as of Jan. 7, 2014 2,524
Percentage of deaths relative to informal settlers in Tacloban City at risk from storm surges 8%
Percentage of deaths relative to entire population of Tacloban City 1.1%
This work is preliminary and a draft of an on-going study.
Census of Population and Housing (2010), National Statistics Office (NSO)
SitRep No. 85 Effects of Typhoon “YOLANDA” (HAIYAN), National Disaster and Risk Reduction and Management Council (NDRRMC)