Philippine Area Of Responsibility Research Articles

About This Special Issue [Meteorology

We are pleased to publish for 2023 this Special Issue on Meteorological Research in the Philippines. Meteorology is a branch of the atmospheric sciences that focuses on the challenging task of reliable weather forecasting. Long-term predictions are extremely difficult to make at high accuracy because the weather is a chaotic physical system that is quite sensitive to initial conditions. Small changes in the initial values that are caused by ambient noise or imprecise measurements can lead to significantly different future dynamical behavior. The Philippines (2020 population: 109,035,343) is prone to extreme weather events. Between 1946 and 2022, an average of 37 ± 8 tropical cyclones (TCs) were formed yearly in the Western North Pacific Basin, with 23 ± 5 of them entering the Philippine Area of Responsibility (PAR) and 10 ± 4 eventually making landfall in the Philippine archipelago. TCs can be categorized into five: super typhoons (max sustained wind speed > 185 kph), typhoons (118–184 kph), severe tropical storms (89–117 kph), tropical storms (62–88 kph), and tropical depressions (< 62 kph). The United States National Oceanic and Atmospheric Administration’s International Best Track Archive for Climate Stewardship database (1950s–2010s) reveals that typhoons (at 80.85 ± 33.95 per decade) were the most numerous— followed by tropical depressions (78.57 ± 38.82), super typhoons (60.2 ± 31.14), tropical storms (56.6 ± 26.34), and severe tropical depressions (52.28 ± 23.8).

SURVEY OF STORM SURGE DUE TO TYPHOON RAI IN DECEMBER 2021 IN THE PHILIPPINES

Typhoon Rai, the last typhoon in the Western Pacific basin in 2021, entered the Philippine Area of Responsibility (PAR) on the 14th December at 23:00 Philippine Standard Time with a minimum central pressure of 985 hPa and maximum sustained winds of 100 km/h (NDRRMC 2022). The typhoon made its first of nine landfalls at Siargao Island in Surigao del Norte on the 16th December 2021 13:30 PST and continued to bring strong winds and rainfall to the Visayas region. The storm was one of the strongest typhoons to have hit the Philippines in recent times, and the government declared a State of Calamity across 493 cities and municipalities (NDRRMC 2022). The typhoon damaged more than 1.1 million houses in the Central Visayas region, and caused a total of 220 total reported deaths and 546 injuries. In the present work, the authors surveyed the storm surge heights in a variety of coastal areas of Cebu and Bohol islands.

EVALUATING HYDROLOGIC MODEL PERFORMANCE OF GLOBAL AND LOCAL WEATHER DATA INPUTS

Abstract. Runoffs from hydrologic models are often used in flood models, among other applications. These runoffs are converted from rainfall, signifying the importance of weather data accuracy. A common challenge for modelers is local weather data sparsity in most watersheds. Global weather datasets are often used as alternative. This study investigates the statistical significance and accuracy between using local weather data for hydrologic models and using the Climate Forecast System Reanalysis (CFSR), a global weather dataset. The Soil and Water Assessment Tool (SWAT) was used to compare the two weather data inputs in terms of generated discharges. Both long-term and event-based results were investigated to compare the models against absolute discharge values. The basin’s average total annual rainfall from the CFSR-based model (4062 mm) was around 1.5 times the local weather-based model (2683 mm). These basin precipitations yielded annual average flows of 53.4 cms and 26.7 cms for CFSR-based and local weather-based models, respectively. For the event-based scenario, the dates Typhoon Ketsana passed through the Philippine Area of Responsibility were checked. CFSR only read a spatially averaged maximum daily rainfall of 18.8 mm while the local gauges recorded 157.2 mm. Calibration and validation of the models were done using the observed discharges in Sto. Niño Station. The calibration of local weather-based model yielded satisfactory results for the Nash-Sutcliffe Efficiency (NSE), percent of bias (PBIAS), and ratio of the RMSE to the standard deviation of measured data (RSR). Meanwhile, the calibration of CFSR model yielded unsatisfactory values for all three parameters.

2020 tropical cyclones in the Philippines: A review

The official website of the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) said more tropical cyclones (TCs) enter the Philippine Area of Responsibility (PAR) than anywhere else in the world. With the average of 20 TCs per year, about eight (8) or nine (9) of them are crossing the Philippines. The peak of the typhoon season is July through October, when nearly 70% of all typhoons develop (http://bagong.pagasa.dost.gov.ph/climate/tropical-cyclone-information). Based on the report of the Asian Disaster Reduction Center (ADRC), five of the typhoons that visit the country are destructive and being situated in the “Pacific Ring of Fire” makes the country vulnerable to frequent earthquakes and volcanic eruptions. Its geographical location and physical environment also contribute to its high susceptibility to tsunami, sea-level rise, storm surges, landslides, flash/flood/flooding, and drought (https://www.adrc.asia/nationinformation.php?NationCode = 608&Lang = en). For the past years, some typhoons that visited the country brought serious damages and kill many Filipinos by floods and landslides. The researcher comes up with the idea of assessing the aftermath of 2020 typhoons that visited the country. The data used by the researcher were collected from different sources, namely NDRRMC (National Disaster Risk Reduction and Management Council), PAGASA, social media and other websites. The result of the study reveals that the most destructive typhoon in 2020 that caused huge damage on the infrastructure and agriculture is Ulysses followed by Rolly, Quinta, Ambo, Vicky, Pepito, Ofel, and Marce. Most of the affected areas are those nearer to water bodies, surrounded by mountains with few trees to absorb a huge amount of water and situated in the low-lying areas.

A climatological study of typhoons over the Philippine Area of Responsibility from 1989–2018

The Philippines is in the Western North Pacific region, where it is a recipient of several weather disturbances such as tropical cyclones. This study aims to determine trends and periodicities of typhoons (TY) within the Philippine Area of Responsibility (PAR), and the rainfall they brought in a 30-year period (1989–2018) for future forecast and disaster risk mitigation efforts of these TY. These TYs are raised when TC’s sustained winds are 118 kph and above. Frequency analysis of TY is done to determine the trends and periodicities in terms of the yearly total occurrence, number of TY that made landfall, distribution of TY classification, and their seasonal variation. The results showed that with PAR the yearly total occurrence of TY seems to have an approximately 12-year periodicity where maximum occurrence was observed around the years 1994, 2004, and 2014 while minimum occurrence was observed in years 1989, 1999, and 2010. Also, track data shows that only 32 % of these TY made a landfall within PAR. Out of the three regions in the Philippines, Luzon Island is the region where most of the severe typhoons made landfall at 80 %. Moreover, TYs occurred mostly during September to November where the transition period between the northeast monsoon and south west monsoon usually occurs. Also, rainfall during which these TYs have occurred were obtained from five synoptic stations across the Philippines. It showed from 1989 to 1998, the total yearly rainfall brought by these TYs ranged from 804 mm to 1 912 mm. But from 1999 to 2018, these TYs brought more rain where their total yearly rainfall ranged from 2 844 mm to 4 941 mm.

One-Dimensional (1D) River Analysis of a River Basin in Southern Luzon Island in the Philippines Using Lidar Digital Elevation Model

Flooding is a perennial problem in the Philippines during the monsoon season intensified by the effects of typhoon. On average, there are 20 typhoons that enter the Philippine Area of Responsibility (PAR), and many of these make landfall causing catastrophic aftermath. Extreme rainfall events could lead to flooding in the downstream floodplain and landslide in mountainous terrains. In this study, which is for the case of Calumpang River that drains to the populated and developing region of Batangas City, the focus is on flooding in the floodplain areas. The river was modelled using LiDAR digital elevation model (DEM) that has an accuracy of 20cm in the vertical and 50cm in the horizontal. The result of this is river hydraulic model that can be used to accurately generate flood inundation simulations and flood hazard maps.

Observed trends and impacts of tropical cyclones in the Philippines

ABSTRACTAn analysis of tropical cyclone (TC) data from 1951 to 2013 in the Philippines revealed that an average of 19.4 TCs enter the Philippine Area of Responsibility (PAR) every year and nine TCs cross the country. Time series analysis of the TC datasets shows no significant trends in the annual number of TCs in PAR but a slightly decreasing trend in the number of landfalling TCs in the Philippines, particularly in the last two decades. However, while the analysis shows fewer typhoons (above 118 kph), more extreme TCs (above 150 kph) have affected the Philippines. The study also confirms that the Northern island of Luzon is most frequently hit by TCs, and that TC‐associated rainfall is greatest in this region compared to the southernmost part of the country. The impact of TCs shows a consistently increasing trend in economic losses and damages. Further understanding of past and future trends of TC activity in the Western North Pacific Basin, and the PAR, including the impacts associated with them, will provide valuable insights for climate change adaptation and disaster risk management.

Identification of storm surge vulnerable areas in the Philippines through the simulation of Typhoon Haiyan-induced storm surge levels over historical storm tracks

Abstract. Super Typhoon Haiyan entered the Philippine Area of Responsibility (PAR) on 7 November 2013, causing tremendous damage to infrastructure and loss of lives mainly due to the storm surge and strong winds. Storm surges up to a height of 7 m were reported in the hardest hit areas. The threat imposed by this kind of natural calamity compelled researchers of the Nationwide Operational Assessment of Hazards (Project NOAH) which is the flagship disaster mitigation program of the Department of Science and Technology (DOST) of the Philippine government to undertake a study to determine the vulnerability of all Philippine coastal communities to storm surges of the same magnitude as those generated by Haiyan. This study calculates the maximum probable storm surge height for every coastal locality by running simulations of Haiyan-type conditions but with tracks of tropical cyclones that entered PAR from 1948–2013. One product of this study is a list of the 30 most vulnerable coastal areas that can be used as a basis for choosing priority sites for further studies to implement appropriate site-specific solutions for flood risk management. Another product is the storm tide inundation maps that the local government units can use to develop a risk-sensitive land use plan for identifying appropriate areas to build residential buildings, evacuation sites, and other critical facilities and lifelines. The maps can also be used to develop a disaster response plan and evacuation scheme.

Probabilistic storm surge inundation maps for Metro Manila based on Philippine public storm warning signals

Abstract. A storm surge is the sudden rise of sea water over the astronomical tides, generated by an approaching storm. This event poses a major threat to the Philippine coastal areas, as manifested by Typhoon Haiyan on 8 November 2013. This hydro-meteorological hazard is one of the main reasons for the high number of casualties due to the typhoon, with 6300 deaths. It became evident that the need to develop a storm surge inundation map is of utmost importance. To develop these maps, the Nationwide Operational Assessment of Hazards under the Department of Science and Technology (DOST-Project NOAH) simulated historical tropical cyclones that entered the Philippine Area of Responsibility. The Japan Meteorological Agency storm surge model was used to simulate storm surge heights. The frequency distribution of the maximum storm surge heights was calculated using simulation results of tropical cyclones under a specific public storm warning signal (PSWS) that passed through a particular coastal area. This determines the storm surge height corresponding to a given probability of occurrence. The storm surge heights from the model were added to the maximum astronomical tide data from WXTide software. The team then created maps of inundation for a specific PSWS using the probability of exceedance derived from the frequency distribution. Buildings and other structures were assigned a probability of exceedance depending on their occupancy category, i.e., 1% probability of exceedance for critical facilities, 10% probability of exceedance for special occupancy structures, and 25% for standard occupancy and miscellaneous structures. The maps produced show the storm-surge-vulnerable areas in Metro Manila, illustrated by the flood depth of up to 4 m and extent of up to 6.5 km from the coastline. This information can help local government units in developing early warning systems, disaster preparedness and mitigation plans, vulnerability assessments, risk-sensitive land use plans, shoreline defense efforts, and coastal protection measures. These maps can also determine the best areas to build critical structures, or at least determine the level of protection of these structures should they be built in hazard areas. Moreover, these will support the local government units' mandate to raise public awareness, disseminate information about storm surge hazards, and implement appropriate countermeasures for a given PSWS.

The Effect of Tropical Cyclones on Southwest Monsoon Rainfall in the Philippines

Intense southwest monsoon (SWM) rainfall events causing massive landslides and flash floods along the western sections of the Philippines were studied. These rainfall events, are not directly coming from the tropical cyclones (TCs) for they are situated far north to northeast of Luzon Island. The heavy rainfall is hypothesized as caused by the interaction of strong westerlies with the mountain ranges along the west coast of Luzon that produces strong vertical motion and consequently generates heavy rainfall. Four of heavy SWM rainfall cases were examined to determine how the presence and position of tropical cyclones in the Philippine vicinity affect these SWM rainfall events; three cases with TC of varying positions within the Philippine area of responsibility (PAR) and the fourth case without TC. Using a spatial Fourier decomposition approach, the total streamfunction is decomposed into two flow regimes: monsoon basic flow (Waves 0-1) and tropical cyclone perturbation flow (Waves 2-23) over a domain of (20°E-140°W, 5°S-35°N). The purpose of this flow decomposition is to determine the latter’s effect on or contribution to the monsoon activity. The analysis utilized the NCEP Final (FNL) data with 1° long. × 1° lat. resolution. Results show that the tropical cyclones over the Pacific Ocean located northeast of Luzon generate strong southwesterly winds over the west coast of Luzon. These in addition to the southwesterlies from the basic flow strengthened the southwest winds that interact with the high Cordillera Mountain ranges

The meteorologically abnormal year of 2006 and natural disasters in the Philippines

In the early part of 2006 the Philippines was hit by a La Nina event which brought floods, flashfloods and landslides. The most significant event was the February 2006 landslide that covered the whole community of Guinsaugon, in Southern Leyte, resulting in 154 deaths with 973 people still missing. Another rare event was the simultaneous presence of two tropical cyclones inside the Philippine Area of Responsibility (PAR) in August- Tropical Depression Bopha and Tropical Storm Saomai-that enhanced the southwest monsoon. With the strong winds and high waves associated with the southwest monsoon, an oil tanker, the M/T Solar 1, sank, resulting in the worst oil spill the country has ever suffered. Lastly, with a weak El Nino phenomenon forming in the Pacific Ocean and affecting the Philippines, a destructive typhoon, Xangsane, made a multi-landfall before hitting Metropolitan Manila. This was followed by the landfall of three supertyphoons- Cimaron, Chebi and Durian-during the last quarter of the year, bringing tremendous destruction of life and property. The occurrence of these weather events are attributed to climate variability the effects of which were exacerbated by a range of factors that include inappropriate land use.