Metropolitan Manila Is a Highly Populated Area and Lies in the Most-Active Tropical Cyclone Basin in the World. Tropica
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Summary: Metropolitan Manila is a highly populated area and lies in the most-active tropical cyclone basin in the world. Tropical cyclones (or typhoons) are strong cyclonic storms that develop over warm ocean waters and when moving across coastal regions can bring immense damage to coastal cities. This report investigates the cascading effects typhoons have had in the past on Metro Manila and looks into possible solution strategies to strengthen the resilience of the urban area. Poverty is one of the most prevalent issues in Manila. Because of improper housing options and poor infrastructure, low-income communities are forced to live in flood-prone areas and therefore highly vulnerable to disaster events that are accompanied by flooding or storm surges. Informal settlements are the part of the urban system most affected by typhoons and in special need for attention in mitigation work. Proposed solution strategies include improvements in urban drainage, inclusive relocation plans, livelihood assistance and capacity building programs, weak solid waste management practices and rehabilitation of the wetland ecosystem. Keywords: tropical cyclones, typhoon, disaster mitigation, flooding, informal settlements, urban poverty, waste management, livelihood assistance, wetland rehabilitation 1 Case study: Manila Stress: Typhoons Author: Vanessa Schaller PROBLEM STATEMENT Metropolitan Manila is a highly urbanized area on the island of Luzon in the Northern Philippines. Due to its geographical location in the Northwest Pacific Ocean it is situated in the most active tropical cyclone basin on Earth (see figure 1a) and is hit by an average of five to seven typhoons every year [1]. Typhoons1 are severe cyclonic storms with wind speeds above 118 km/h.2 They form in the tropical oceans over warm sea surface waters and if wind conditions are favourable grow into large formations of stormy clouds and spiralling winds. Moving at an average speed of about 19 km/h and guided by the main airstreams above them, they usually travel north-westward through the Northwest Pacific Ocean towards the Philippines, China and Japan (see figure 1b). Most typhoons generally last for about 6 days before they reach land, where they dissipate because of increased friction and moisture cut-off. They can however strengthen again when travelling out into the sea and last up to 2 weeks [2]. Nearly 70% of the cyclones in the Northwest Pacific basin develop from July to October, and although there is a minimum chance of occurrence in February there is no specific typhoon season and they regularly occur all year round [3]. Figure 1: a) Map of all tropical cyclone tracks from 1945-2006. Cyan and blue tracks correspond to tropical storms, yellow, orange and red tracks show storms classified as tropical cyclones (maximum windspeed >118 km/h). It can be seen that the Northwest Pacific Ocean (marked by a rectangle) is the basin where most tropical cyclones occur worldwide. b) Tracks of all tropical cyclones of the 2019 Northwest Pacific season. The storms typically form over the ocean and move north-westward towards the coastlines. The points show the location of each storm in 6-hour intervals. The color code corresponds to the one explained in a). The location of Metro Manila is indicated by a red star. Figures adapted from [4] and [5]. 1 The terms ‘tropical cyclone’ and ‘typhoon’ are two different names for the same phenomenon. Throughout this text ‘tropical cyclone’ is used for more generic information, while the term ‘typhoon’ is used when specifically referring to a tropical cyclone in the Northwest Pacific basin. (In the Atlantic and Northeast Pacific Ocean tropical cyclones are also referred to as hurricanes.) 2 as defined by the ESCAP/WMO Typhoon Committee [38] 2 Typhoons are one of the most destructive natural disasters and heavily impact coastal areas in the Northwest Pacific basin. They often make landfall in the Philippines and bring heavy rain, strong winds and storm surges with them. With a yearly average of 20 typhoons, the Philippines is the area 3 most affected by tropical cyclones is in the world [3]. The last cyclonic storm that heavily impacted the capital Manila was Typhoon Kammuri4 in December 2019. Almost 450.000 people were evacuated and half a million buildings were damaged in Metro Manila alone [6]. Marina traffic was suspended and Manila’s airport shut down for 12 hours resulting in the cancellation of over 500 flights [7]. Reports like this are not untypical for Manila. In 2009 Typhoon Ketsana5 caused severe flooding in the Metropolitan area [8]. It led to an economic damage of 233 million US dollars and killed over 400 people 6, making it one of the most destructive typhoons in Philippine’s history [9]. Because of the frequent occurrences of typhoons and the city’s location in a seismically active region, Manila was deemed the second riskiest city7 to live in, in terms of natural hazards [10]. And yet, with almost 13 million people8, the Metro Manila area is one of the most densely populated metropolitan areas in the world [11]. Although most of the typhoons that hit Manila on a regular basis are not affecting the city as severely as Typhoon Ketsana did, one can use Ketsana as a case study to infer what possible cascading effects typhoons imply for the Manila area. Typhoon Ketsana led to widespread flooding as an effect of a record high rainfall event of 455 mm in 24 hours [12]. Flood waters covered almost 80% of the Metro area, ranging from knee-deep up to roof-top- deep water levels. The heavy rain also caused landslide incidents, that together with floodwater led to numerous impassable road sections. Over 4 million people in Metro Manila were affected by the disaster. The economic damage was mainly composed of damaged infrastructure and agricultural loss. In total over 180.000 buildings were destroyed and 300.000 megatons crops lost [9]. Typhoon Ketsana showed the vulnerability of the city to the effects of cyclonic storms, but it also ignited stronger efforts in mitigation works. In general, the effects of a natural disaster can be categorized into groups of primary, secondary and tertiary hazards. The primary hazards of typhoons consist mainly of heavy rainfall and destructive winds. However, the greatest damage to life and infrastructure is caused by secondary hazards such as storm surges, flooding, landslides and tornados. Tertiary hazards include spikes in food prices and other necessities, but also effects that can follow years after the typhoon. At sea, typhoons primarily impact shipping logistics by causing distress for vessels and forcing ships to reroute. As a consequence, entire supply chains can be disrupted or delayed. The most significant effects of typhoons however, occur when they cross coastlines. Primary effects are destructive winds, that can damage buildings, bridges, vehicles and trees and turn loose material into dangerous flying projectiles. The heavy rainfall primarily intensifies storm surges, causes flooding and landslides. Storm surges are typically the most dangerous effects of landfalling cyclones to human life and historically caused 90% of all tropical cyclone deaths by drowning [13]. Flooding in combination with destruction of sanitation 3 It is referred to the Philippine Area of Responsibility, the area monitored by the Philippines’ national meteorological agency. 4 Kammuri is the international name, it is also known as Typhoon Tisoy in the Philippines. 5 Ketsana is the international name, it is also known as Typhoon Ondoy in the Philippines. 6 The numbers refer to the damage and casualties in Metro Manila only. 7 ranked by potentially affected people 8 Number of inhabitants of the National Capital Region from the last census in 2015. Likely to be more now. 3 facilities leads to sewage polluted water bodies and, in case of stagnant waters, can cause the spread of infectious water-borne diseases. Secondary effects also include disrupted power lines and communication networks as a result of destroyed utility towers. Additionally, clean water supply can also be a prevalent issue resulting from infrastructure damage, and blocked roads can complicate rescue efforts and transportation of food and medication. In the aftermath of a typhoon the biggest issues usually are providing enough shelter solutions for the homeless and covering the financial needs for reconstruction. In addition to that, experiencing a disaster and witnessing death or destruction of the home can have psychological consequences for individuals. Mental health issues are often underestimated and don’t receive much attention from public health authorities [14]. Typhoons also impact the coastal wetland ecosystems. Saltwater intrusion induced by storm surges can affect both marine animals and animals living in the coastal wetland. Damage and change of their habitat following a disturbance can lead to a decrease in species diversity. Also, the destruction and loss of mangrove forests by uprooting and other changes in the tree canopy have been observed. Moreover, the effects of typhoons cause extensive beach erosion and thereby reshape the morphology of the coastline [15]. These effects may reduce the future ability of wetland ecosystems to protect the land from storms by dampening the resulting surges. Like most other weather phenomena, tropical cyclones are expected to become more extreme with climate change. Most experts agree that the number of cyclones will become less, however, their maximum intensity and related rainfall will increase [16]. A study has shown that over the past 37 years landfalling typhoons in the Northwest Pacific have intensified by 12 to 15% and linked this effect to ocean surface warming [17]. Also, a north-westward shift of typhoon tracks after the late 1980s has been reported [18]. Climate model projections of tropical cyclones worldwide predict that a 2°C anthropogenic global warming will lead to an increase of 14% in cyclone precipitation rates, a 5% increase in maximum surface wind speed and a proportional increase of very intense storms by 13%.