Alfredo Mahar Francisco Lagmay (a, b), Rojelee P. Agaton (b), Mark Allen C. Bahala (b), Jo Brianne Louise T. Briones (b), Krichi May C. Cabacaba (b), Carl Vincent C. Caro (b), Lea L. Dasallas (b), Lia Anne L. Gonzalo (b), Christine N. Ladiero (b), John Phillip Lapidez (b), Maria Theresa Francia Mungcal (b), Jose Victor R. Puno (b), Michael Marie Angelo C. Ramos (b), Joy Santiago (b), John Kenneth Suarez (b), Judd P. Tablazon (b)
(a) National Institute of Geological Sciences, University of the Philippines, Diliman, Philippines,
(b) Nationwide Operational Assessment of Hazards, University of the Philippines, Diliman, Philippines
On 8th November 2013, Typhoon Haiyan, local name Yolanda, made landfall in the central Philippine islands region. Considered one of the most powerful typhoons ever to make landfall in recorded history, the 600 km diameter Typhoon Haiyan crossed the Philippine archipelago, bringing widespread devastation in its path. Strong winds, heavy rainfall, and storm surges caused extreme loss of lives and widespread damage to property. Storm surges were primarily responsible for the 6300 dead, 1061 missing and 28,689 injured in Haiyan’s aftermath. Here, we document the storm surge simulations which were used as basis for the warnings provided to the public 2 days prior to the howler’s landfall. We then validate the accounts based on field data and accounts provided in the news. The devastating Haiyan storm surges are one of the biggest in several decades, which exacted a high death toll despite its early prediction. There were many lessons learned from this calamity, and information contained in this work may serve as useful reference to mitigate the heavy impact of future storm surge events in the Philippines and elsewhere.
Haiyan is one of the most powerful typhoons to have made landfall in recorded history, with maximum sustained winds reaching 315 kph (170 knots) with gusts up to 379 kph (205 knots) just before landfall. This makes it equivalent to a Category 5 typhoon on the Saffir–Simpson hurricane scale, which has the capacity to cause catastrophic damage, a high percentage of destruction of framed homes, total roof failure and wall collapse, isolation of residential areas due to fallen trees and power poles, and power outages that could last for weeks and possibly months .
It started as a region of low pressure in the West Pacific Ocean early on 2nd November 2013 and was upgraded to a tropical storm (TS) with the name Haiyan after subsequent intensification. Upon entry of the typhoon into the Philippine Area of Responsibility (PAR), the Philippine Atmospheric Geophysical Astronomical Services Administration  gave it a local name of Yolanda. Regular 6 hourly bulletins on the severe weather disturbance were issued by the Philippine weather bureau with short updates given every hour. Typhoon Haiyan made landfall in Guiuan, Eastern Samar on 8th November 2013 at 04:40 AM local time.
By 7th November, storm signal warnings had been raised by PAGASA, including storm surge warnings in many parts of the country. Typhoon Haiyan hit the eastern part of the Philippines on 8th November, following a track heading towards the West Philippine Sea (South China Sea), crossing the majority of the Visayas region (Fig. 1) at a speed of 40.7 kph (22 knots) . Haiyan maintained its structure as it moved over the east central Philippines. JMA observed that the lowest value of central pressure was 895 hPa (very low central pressure means very high wind speed) and typhoon intensity increased from “very strong” to “violent” .
In terms of wind speed, the Joint Typhoon Warning Center  touted Haiyan as the most intense tropical cyclone in the world for 2013. As Typhoon Haiyan traversed through the country, it caused damage to houses and infrastructure, flooding in low-lying areas, landslides and storm surges. Initial simulations reveal storm surges to have inundated an estimated 98 km2 in Leyte and 93 km2 in Samar, two of the most devastated islands in the Philippines. Other coastal areas in the central Philippines region also experienced floods due to storm surges. Super Typhoon Haiyan is the deadliest typhoon ever to hit the Philippines in recent history leaving 6300 dead, 1061 missing and 28,689 injured.
The storm surges of Haiyan were predicted two days in advance with a complete list that was broadcast over media the night before Haiyan made landfall. Unfortunately, despite the advanced warnings, these were not translated into appropriate action in every coastal village in the Central Philippines region. Here we elucidate the process behind the storm surge forecast for Haiyan, assess its suitability for early warnings, enumerate the lessons learned from the disaster and then recommend measures to prevent the same mistakes from happening again in the future.
2. Storm surge forecasting method
To forecast the storm surges of Typhoon Haiyan, research scientists of the Nationwide Operational Assessment of Hazards (DOST-Project NOAH), the flagship disaster research program of the Department of Science and Technology, used the Japan Meteorological Agency (JMA) Storm Surge Model. At that time, the storm surge component of Project NOAH had only just been established and the Typhoon Haiyan event was the first time it released storm surge forecasts publicly. The JMA Storm Surge Model that was used is a numerical code based on two-dimensional shallow water equations and is used to simulate and predict storm surges mainly caused by tropical cyclones. Storm surge values are calculated from the wind set up due to the strong onshore winds above the sea surface and the inverse barometer effect associated with the sudden decrease of pressure in the atmosphere. Storm surge height predictions can be made up to 72 h ahead of landfall . Each calculation takes about 20 min, and storm surge distribution maps are created using the results. Parameters used as input for the storm surge model include bathymetry, storm track, central atmospheric pressure, and maximum wind speed. These inputs determine the accuracy of simulation results.
The model only accepts 2-min or 5-min grid resolution for bathymetry, as such; ETOPO2 data with grid postings every 2′ was used. Bathymetry was a necessary parameter input in the JMA model since the slope of the sea floor influences the height of the storm surge. Wide and gently-sloping sea floor produces higher storm surge heights, while narrow and steeply-sloping shelves produce lower storm surge heights .
The predicted storm track used was from JMA, freely available to the public and available for download at http://www.wis-jma.go.jp/. JMA releases tropical cyclone forecasts every 3 h. Apart from the storm track, atmospheric pressure and maximum wind speed were also derived from JMA. Generated storm surge height values within the swath of the 600 km wide typhoon for pre-selected coastal sites of the Philippines, were then added to the data from WXTide – software that contains a catalog of worldwide astronomical tides. Addition of the storm surge height to WXTide generates the storm tide values. These were used by DOST-Project NOAH to warn the public through PAGASA, of this type of hazard associated with Typhoon Haiyan.
3. Storm surge model results
96-h storm surge forecasts were generated for Typhoon Haiyan covering 2013-11-06 00:00:00 to 2013-11-10 00:00:00 UTC (Fig. 2). The simulations were updated three times using the forecasted tracks from JMA. The forecasts had to be continuously updated as predicted storm tide heights and peak surge times change depending on the forecasted tropical cyclone track data.
The first simulation used JMA’s forecasted track data from 2013-11-06 11:00:00 UTC. The time series plots for 149 coastal sites were released to the public on the same day via the Project NOAH website. The plots show the predicted time of the peak surge and the trend of the water level changes every 10 min for the duration of the simulation. Ormoc City in Leyte had the highest predicted storm tide height at 5.04 m (Fig. 3a), but in the succeeding simulation became 10th in the list with a height of 3.8 m.
The second simulation made with 2013-11-07 11:00:00 UTC data was used for the official list of the highest predicted storm surge and tide values. This was also released on 7th November and sent to the Office of Civil Defense (OCD) and the NDRRMC. The time series plots for the localities with the highest peak storm tide heights are shown in Fig. 3b. The highest predicted storm tide height was 5.3 m for Matarinao Bay, Eastern Samar, which covers the towns of Salcedo, Quinapondan, Gen. MacArthur and Hernani. The official list of 68 localities provided to the NDRRMC is shown in Table 1. No less than the President of the Republic of the Philippines announced the severity of the impacts of the storm surges on primetime television. Included in his speech was reference to the DOST-Project NOAH website (http://noah.up.edu.ph), where the list of storm surge heights can be found.
|Province||Location||Storm tide (m)||Date||Time of peak height|
|Eastern Samar||Matarinao Bay||5.3||11/8/2013||9:50:00|
|Biliran||Poro Island, Biliran Strait||4.7||11/8/2013||12:10:00|
|Leyte||Tacloban, San Juanico Strait||4.5||11/8/2013||11:00:00|
|Eastern Samar||Andis Island, Port Borongan||4.3||11/8/2013||9:30:00|
|Quezon||Santa Cruz Harbor||4.2||11/9/2013||2:20:00|
|Northern Samar||Helm Harbor, Gamay Bay||3.7||11/8/2013||9:10:00|
|Negros Occidental||Himugaan River Entrance||3.1||11/8/2013||14:00:00|
|Camarines Sur||Cabgan Island, San Miguel Bay||2.9||11/8/2013||8:10:00|
|Camarines Norte||Lamon Bay:Apat Bay||2.9||11/8/2013||9:00:00|
|Oriental Mindoro||Port Concepcion, Maestre de CampoI||2.8||11/9/2013||1:20:00|
|Albay||Tabaco, Tabaco Bay||2.7||11/8/2013||9:20:00|
|Oriental Mindoro||Calapan Bay||2.7||11/9/2013||1:30:00|
|Leyte||Canauay Island, Janabatas Ch||2.7||11/8/2013||12:00:00|
|Negros Occidental||Danao River Entrance||2.6||11/8/2013||14:30:00|
|Camarines Sur||Tabgon Bay||2.5||11/8/2013||10:20:00|
|Negros Occidental||Carcar Bay||2.5||11/8/2013||14:40:00|
|Aklan||Aclan River Entrance||2.5||11/9/2013||1:40:00|
|Capiz||Libas (Capiz Landing)||2.4||11/8/2013||15:30:00|
|Camarines Norte||Port Jose Panganiban||2.3||11/8/2013||8:50:00|
|Camarines Norte||Lamon Bay:Capalonga||2.3||11/8/2013||8:40:00|
|Occidental Mindoro||Apo Island, Mindoro Strait||2.2||11/9/2013||1:10:00|
|Batangas||Anilao, Balayan Bay||2.2||11/9/2013||1:10:00|
|Eastern Samar||Hilaban Island||2||11/8/2013||8:50:00|
|Samar||Uban Point, San Juanico Strait||2||11/8/2013||9:00:00|
|Camarines Norte||Guintinua Island, Calagua Islands||2||11/8/2013||9:20:00|
Table 1. Predicted storm tide for Typhoon Haiyan, 2 m and above.
A third simulation was made using 2013-11-06 17:00:00Z JMA data and the time series plots on the website were updated using these results (Fig. 3c). Places in the list of 10 highest predicted storm tide are consistent in the three simulations, with the highest storm tides found mostly in Leyte and Eastern Samar, where the typhoon was expected to make landfall (Fig. 1). Storm surge events during Typhoon Haiyan have also been recorded in many of these areas. After the typhoon, inundation models and field surveys were done to assess the coastal flooding (see Section 4.4 Assessment of Storm Surge Inundation).
4.1. Storm surge inundation Maps
Aside from the storm tide height forecasts, existing storm surge hazard maps were already available at the time of the disaster. These maps were from the READY Project, which is a joint effort in risk mapping among government and donor agencies. The aim of the project is to reduce the problem of disaster risk management (DRR) at the local level by empowering the most vulnerable cities and municipalities in the country and enable them to prepare disaster risk management plans. The project hopes to develop a systematic approach to community disaster risk management. Supported by the United Nations Development Program (UNDP) and the Government of Australia Australian Aid (AusAID), storm surge hazards maps are among the outputs of the project, shared with the sub-national government units or communities and integrated into their local comprehensive development or land use plans . READY hazard maps are made available to communities through the preparation of printed maps and also online through the National Mapping and Resource Information Agency (NAMRIA) Geoportal, among others. Fig. 4 shows the READY map for Tacloban. The purple color refers to an inundation height of 1–4 m. Based on reported storm tide heights and field data, this range is an underestimation of the maximum storm surge levels and extent.
4.2 Pre-emptive Action
Because of the weather bulletins issued by PAGASA, work and classes were suspended on 7–8 November in several provinces in the path of the typhoon. Each city and municipality has the authority to declare suspensions and base their decisions mainly on bulletins provided by the Philippine Weather Bureau, supplemented by information from other international and local sources, including those posted by DOST-Project NOAH on its website and mobile applications.
Regional offices of the Department of Public Works and Highways (DPWH) conducted assessments of structural integrity of schools, cleaning of waterways and drainages, clearing of roads and pruning of trees. Response teams and heavy equipment were put on standby. The Department of Health (DOH) prepositioned medicine, and first aid kits and placed hospitals on alert . The Armed Forces of the Philippines had the Naval Forces Southern Luzon (NAVFORSOL) dispatch trucks, relief goods, diving gear, rubber boats, portable generators and squad tents in Albay. The Philippine Navy was placed on alert and directed all its floating assets to prepare and take necessary precautionary measures for the typhoon .
The Tacloban local government unit also evacuated people near the coast and had food packs ready . The DOH in Tacloban also augmented their stock of medicine and body bags. In Eastern Samar, Governor Conrado Nicart Jr., said they had rescuers and rescue boats on standby before Typhoon Haiyan hit the province . In the provinces of Capiz and Iloilo on Panay Island, forced evacuation of residents in coastal villages was implemented up to 2 days before the typhoon made landfall. The newly installed Doppler radar station in Guiuan, where the typhoon first made landfall, provided images of the incoming typhoon and was used as part-basis for the issuance of warnings given 2 days prior to landfall. The mayor of Guiuan informed all barangay (village) officials to evacuate. Some residents evacuated, some did not . In Manicani Island in Guiuan, pre-emptive evacuation was implemented and barangay officials also explained to residents what a storm surge was and could do. Later it was learned that out of 3000 residents, the island only had 1 casualty . Furthermore, succeeding field surveys reveal that the provinces of Capiz and Oriental Mindoro issued forced evacuation orders at least a day before the typhoon. Calapan City in Oriental Mindoro also issued evacuation orders based on PAGASA and Project NOAH’s warnings (see Fig. 1 – location map). In Iloilo province, municipality of Carles, with a total population of 62,690, experienced storm surges 4–5 m high. These storm surge heights were about the same as those that hit Tacloban and Tanauan, Leyte but only 32 people died in this municipality .
4.3. News accounts
Coverage of Haiyan’s aftermath was in both local and international news. Although the devastation was widespread in the central Philippines region, attention was focused in Tacloban City, where national government officials and many of the weather news crews tasked to cover the Super typhoon positioned themselves.
According to the provincial government of Leyte, the storm surge was estimated to reach as high as the equivalent of three floors of a building . Others estimated the waves that flattened Tacloban, destroyed most of the houses, upturned vehicles on the road, and took the life of thousands, to be 20 feet high . In Samar, where the typhoon made its first landfall, reports of a storm surge as high as five meters filled the roads with debris . In the coastal towns of Basey, Samar the local government was paralyzed after it was hit by a 15-feet storm surge . Eyewitness accounts of the storm surge height vary and must be validated to establish accuracy and reliability of data.
4.4. Assessment of storm surge inundation
After the Haiyan disaster, a FLO-2D simulation of storm surge inundation in Tacloban City was generated to assess the extent of incursion of seawater inland. FLO-2D is a two-dimensional flood routing model with the continuity equation and the dynamic wave momentum equation as the governing equations of the model (Flo-2D, 2013). The storm tide time series generated from JMA combined with the WXTide values and a 5-m resolution digital elevation model derived from interferometric synthetic aperture radar (IFSAR) were used in the storm surge inundation model.
On 30th November 2013, researchers of DOST-Project NOAH conducted field validation and interviews in Tacloban regarding the storm surge brought by Typhoon Haiyan. Interviewees were present during the storm surge event; their first-hand accounts of the event were recorded to help validate the result of the simulation. In other areas with no witnesses of the storm surge event, the team searched for watermarks to determine the highest level the water reached. The high watermarks pointed out by the interviewees were measured vertically relative to the ground using a meter tape. Based on the survey, water levels reached 4–5 m in the village of San Jose and the surrounding areas of the airport. The downtown area of Tacloban experienced 5–6 m of flooding due to the storm surge.
In a separate field study conducted in Eastern Samar, the municipalities of Salcedo, Quinapondan, Gen. MacArthur and Hernani along Matarinao Bay had high coastal flood depths ranging from 3 to 5 m, which are consistent with the JMA Storm Surge Model forecast.
The Japan Society of Civil Engineers (JSCE)–Philippine Institute of Civil Engineers (PICE) Typhoon Haiyan Joint Survey also conducted field surveys in the areas affected by Haiyan . Their data were also used to validate the results of the JMA storm surge model combined with the FLO-2D inundation model (Fig. 5).
Based on the field estimates, the second JMA Storm Surge simulation compares well with the reported heights but the time of peak surge was late by almost four hours. The predicted time for Tacloban was 11:00 AM local time, but according to reports, the storm surge hit between 7:00 and 8:00 AM. The discrepancy is due to differences between the forecasted track and forward speed of the typhoon and its actual path. The 4.5 m (14.7 feet) prediction for Tacloban was also consistent with some eyewitness accounts saying that the storm surge there reached 15 feet. In the succeeding simulation, the predicted peak time was now earlier at 10:00 AM local time but the predicted storm surge level was lower at 3.5 m.
Comparing the field data to the inundation map generated using FLO-2D, the storm surge inundation model underestimated the depth of the coastal flooding. The root mean square error for the validation points is 1.44 m. A table showing the height of the simulations and the validation points is shown in Table 2. Although the root mean square error is above a meter in height, the extent of the 3 most inland validation points are consistent with the flood map that was generated (see Fig. 5). However, it is recommended that the inundation model be recalibrated to improve the results. This may include adding Manning’s roughness coefficients and using a more accurate storm tide hydrological input.
|Location||Measured height from ground (m)||Model (m)|
|Brgy 69, Tacloban||0.8||2.03|
|LY 891Brgy Tigbao||1.7||0.09|
|LY 891Brgy Tigbao||2.5||0.03|
|Brgy 69/70, Tacloban||1.3||2.98|
|Brgy 1 & 4 Trece Martires(Port of Tacloban)||3.6||1.93|
|Leyte Park Hotel Brgy 1 & 4, Tacloban City||0.3||2.34|
|Brgy 1 & 4 Trece Martires||2.4||1.91|
|Brgy 74 Lola Tula||3.1||2.28|
|Brgy 74 Lola Tula||0.9||2.19|
|Brgy 1 City Proper, Tacloban||2.6||2.63|
|Brgy 91 Abucay, Tacloban||1.3||2.31|
|Brgy 38 & 65, Tacloban||1.3||2.31|
|BM 889 Brgy 71||1.8||0.21|
|Philhealth Office Brgy 25 City Proper, Tacloban||1.1||0.77|
|Brgy 54A, Tacloban||8.60 (?)||4.66|
|Brgy 88 D. Z. Romualdez Airport, Tacloban||4.2||2.36|
|Covention Center, Brgy 62 Sagkaan, Tacloban||3.1||2.86|
|Brgy 77 Fatima Village, Tacloban||3.9||2.62|
|Brgy hall Brgy 88 San Jose, Tacloban||4.2||2.96|
|Brgy 85 San Jose, Tacloban||3.3||2.88|
|Brgy Marasbaras, Tacloban||0.7||0.16|
|Philippine Port Authority, Tacloban Port||3.44||3.42|
|Security Gate of TESDA, Tacloban Port||2.98||2.31|
|TESDA, Tacloban Port||2.74||1.54|
|Barangay 83-A, Tacloban||4||2.4|
|Barangay 88, Tacloban||4.6||2.84|
|Barangay 78, Tacloban||3||1.79|
|Barangay 45, Tacloban||3.5||2.25|
|Barangay 6A, Tacloban||2||2.1|
Table 2. Measured height vs modeled inundation depth.
4.5 Interviews with Tacloban City Residents
Interviews with Typhoon Haiyan survivors were conducted to find out how they prepared for the Super Typhoon, what happened when the storm surge hit, and how people were able to survive. According to eyewitnesses in Tacloban, the water level rose to 15 feet in 20 min. The storm surge did not just come from the direction of the sea but also from the airport and had moved like a whirlpool. People survived by climbing up trees or roofs. They said that the local government had roving jeeps with bullhorns warning them to evacuate the night before Haiyan’s landfall.
Some people did not evacuate because they either wanted to protect their property or they thought their concrete-built houses were safe. Tacloban is often hit by typhoons but based on their experience, typhoons only bring wind and rain and it was the first time a storm surge happened there. Several evacuation sites proved disastrous because they were overwhelmed by storm surges (Fig. 5).
A university administrative staff said that those areas damaged by storm surges should be made into permanent danger zones, and that a hazard map of the area is necessary. The same person said that if a tsunami alert had been given, residents might have listened to the evacuation orders. Some of the informal settlers who were interviewed said that a barangay captain warned them of a tsunami, the night before the storm. One resident narrated that several hours after the deluge in Tacloban, someone shouted “Tsunami” and caused panic among some residents. The mad rush towards higher ground resulted in injuries. Another interview said that around 100 people went up the hills beside the coast and survived while those who did not believe the warning and stayed in their houses did not make it.
5. Conclusion and recommendations
5.1. Population vs death toll
Compared to the killer storm surge events on 12th November 1970 and 29 April 1991 in Bangladesh, which caused 300,000 and 138,882 deaths, respectively , the death toll of Haiyan is 6300 with 1061 still missing. Many of the casualties of Typhoon Haiyan are from Tacloban City and its adjacent southern municipalities of Palo and Tanauan (Table 3). These areas rank among the top 3 highest percentage number of fatalities relative to the population. Based on these metrics, it is clear that the number of deaths is not only related to the landscape of the affected areas and proximity to where the eye of the typhoon made its initial impact but also with the population.
|Municipality/City||Number of deaths ||Actual population ||Percentage of death relative to total population||Province|
Table 3. Top ten cities/municipalities with fatalities caused by Typhoon Haiyan.
5.2. Storm surge forecasting
Meteorological factors that affect storm surge models include wind speed, pressure, and storm track. Physical factors, on the other hand, are near-shore bathymetry, coastal shape, and topography. The height of the surge highly depends on the strength of the winds carrying it. However, physical factors are also important to consider. For example, a storm surge is more dangerous in areas with a gently sloping seafloor, as there is no barrier for the waves to stop the surge from going further inland. Storm surge prediction requires the input of all the abovementioned factors in the storm surge model to create accurate hazard maps.
The JMA Storm Surge Model was convenient and practical to use before Typhoon Haiyan’s landfall because it was easy to set up and had a quick runtime. The storm surge forecast was made 2 days before Haiyan’s impact, enough time to warn affected areas for appropriate response. The 4.5 m (14.7 feet) prediction for Tacloban was also consistent with some eyewitness accounts saying that the storm surge there reached 15 feet. The number one in the list of predicted storm surge heights was Matarinao Bay, Eastern Samar. In the municipality of Hernani, Eastern Samar, at the mouth of Matarinao Bay, the highest storm surge height validated by our team was 5 m.
Based on the comparison of the field validation of Project NOAH staff and JSCE–PICE with the simulated inundation map, the flood depth and extent was underestimated in some areas of Tacloban. However, the forecast was still able to determine the areas likely be affected by storm surges. Although the accuracy of the results depended on the predicted typhoon track and bathymetric data, which was not that exact, the forecasting process was nevertheless suitable for use as a tool for early warning.
5.3. Hazard exceeding precedent
Even with the warnings, the typhoon was simply too powerful and the storm surge that levelled many communities was unprecedented. Tacloban City, one of the hardest hit places by the typhoon, accounted for 2500 of the over 6000 total deaths. Tacloban’s location, its low elevation, its urbanization, and its dense population are factors that contribute to its susceptibility to storm surges. It is bordered on the east by the San Juanico Strait that stretches to the Pacific Ocean and on the south by the San Pedro Bay that stretches to the Leyte Gulf. Tacloban is also bordered on its north and the west by mountains, effectively trapping the storm surges that swept inland. From field surveys, the extent of the storm surges reached at least 2 km inland, which was not reflected in earlier storm surge hazard maps. A plot of the evacuation centers in Tacloban show how they positioned relative to the storm surge hazard map (see Fig. 5).
5.4. Communication challenges and Poor local response
The storm surges of Typhoon Haiyan were predicted 2 days in advance with a complete list that was broadcast over tri-media and social media. DOST-Project NOAH hosted the list of areas that were to be affected by storm surges, which identified specific places and heights. That warning was echoed by no less than the President of the Philippines over primetime television on the eve of Haiyan’s landfall. Unfortunately, despite the advanced warnings, these were not translated into appropriate action in every coastal village in the Central Philippines region.
Storm surge hazard maps from the READY project, which existed 7 years prior to the impact of Typhoon Haiyan did not reflect the actual storm surge flood extent. This is due to the difficulty in predicting a Haiyan strength scenario, which was an extreme event in the historical record. The discrepancy in the depiction of storm surge inundation is due to limits in the methodology used in generating the hazard map. Since high-resolution topography derived from airborne LiDAR (vertical accuracy of 0.15 cm) and IfSAR (vertical accuracy of 0.5 m) surveys were not available then, base maps were too crude to create hazard maps with good accuracy in terms of flood distribution, height and extent . With ample warning of storm surges, it is necessary that the community have reliable hazard maps to base appropriate action upon. The last thing that we want to happen is for residents in the warned community to move from one unsafe place to another unsafe place. And it is only with a reliable storm surge hazard map that anyone can really determine where safe areas from storm surges are located. The Philippine government invested heavily in LiDAR and IfSAR for flood and storm surge simulations (see Fig. 5) and were already being utilized . However, the Haiyan catastrophe got ahead of the detailed hazard mapping efforts using LiDAR and IfSAR as base topography.
Also, not everyone knew what a storm surge was and what it could do. People were more familiar with the term tsunami and the word storm surge was new to them. Although disaster responders encouraged people to leave the coastal villages of Tacloban, there was still difficulty in getting everyone out of harm’s way. There are many reasons that compound the situation, making complete evacuation of residents hard to implement: The coastal towns hit by the storm surge have large communities of informal settlers, and they are some of the most vulnerable to disasters due to their high population density and flimsy-built housing. In some communities, there is a local belief that they know their sea better than anyone else, which also hindered evacuation. The clear skies the night prior to the typhoon also made it appear that a catastrophe was not imminent. There were also news reports that men in some areas had stayed behind to guard their houses. Two historical storm surge events had previously devastated Tacloban—one in 1897 which killed up to 1500  and another in 1912 which killed 15,000 people —but the residents were not aware of these and had not learned from history. Further, there is also the assumption that common folk are generally disinterested in learning about hazards because daily concerns are more important and at that time, political issues related to corruption had diverted media attention. For the people that did evacuate, some of them still fell victims to the typhoon as 68% of evacuation centers were overwhelmed by storm surges (Fig. 5). In the final analysis, even if the people knew exactly what a storm surge was, if they did not know the location of safe evacuation sites due to the absence of detailed and accurate maps, loss of lives would still be inevitable.
To prevent an impending disaster, there are two important points to consider: (1) Warning and (2) Action (Response). The warning must be accompanied by knowledge by the people on what to do in case the alarm is raised. For Haiyan affected areas, the storm surge warning was raised days in advance but incomplete action was made to prevent the loss of lives by the thousands. This was complicated by a variety of reasons as mentioned above. However, it is important to note that there must have been preparedness action made by the communities since the extremely devastated places are coastal areas which had on average about 99% of their population survive.
To achieve a much lower fatality count, there is a need to strengthen hazards education at the barangay (village) level and develop a culture of preparedness. Although this is already embodied in section 12 articles 9 and 10 of Republic Act no. 10121 , its actual implementation leaves much to be desired.
Moreover, reference to more detailed maps that depict the scenario of inundation for any given storm surge warning is imperative. Maps that are low resolution and developed through field interviews are insufficient or too crude because anecdotal accounts can be incomplete. Detailed maps can only be created through highly accurate digital terrain models (DTMs), surveyed through Light Detection and Ranging (LIDAR) or equivalent survey instruments. Computer models of storm surge inundation are made on these high-resolution DTMs, printed out for display for each barangay or shown through the internet for reference by the public to know the action to take when there is a warning. The public will want to move from an unsafe place to a place that is safe based on the detailed storm surge hazard maps.
The Philippines is visited by 20 cyclones each year and storm surges are common. The one that happened in the central Philippine region during Haiyan is perhaps the most powerful in recent history and it will not be the last of its kind. The sooner the detailed and high-resolution storm surge hazard maps are created, the better the people can respond to any warning of an impending storm surge hazard.
We wish to acknowledge the Department of Science and Technology (DOST) for funding the project (Grant no. 6234), Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA), Nationwide Operational Assessment of Hazards (Project NOAH) and the University of the Philippines National Institute of Geological Sciences (UP NIGS) for their support, the Japan Meteorological Agency (JMA) for the use of their software, and the JSCE-PICE Typhoon Haiyan Joint Survey Team for their field data.
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