Methods and Limitations
HazardHunterPH consumes existing information as provided by agencies to the GeoRiskPH Integrated System. Since some data used for calculations may be outdated, GeoRiskPH will not be liable for results that may differ from actual data. Also, hazards information may be refined and updated as new data become available to the system.
For point data for schools and health facilities, they may not represent the actual location of the facility and may need further verification. Similarly, administrative boundaries and the scope of the hazard may not fit well when calculating for their intersection. Hence, users are advised to view the hazard map overlain with the administrative boundary layer to visually verify how much of the area is within the scope of the hazard. Lastly, it should be noted that administrative boundaries used are only an approximate and are not considered authoritative.
Calculation for the level of exposure or proneness of barangays to hazards incorporates the slightest intersection between the barangay boundary and hazard layers. Values for prone population, schools, and health facilities per barangay, and prone barangays per municipality were summed up to obtain the values shown on the table. In the absence of data for built-up areas, population density figures per barangay were obtained by evenly distributing population across each barangay.
Barangays prone to hazard = barangays ∩ hazard
Population prone to hazard = population density * (barangay area ∩ hazard area)
Facilities prone to hazard = barangays ∩ hazard ∩ facilities (Note: Facilities may be schools or health facilities)
The NAMRIA generated the Open Spaces (for NCR) using the following criteria:
1) Land use is Open/Vacant Space;
2) Area at least 200 square meters; and
3) Located outside the radius of 1.5 x the height of the adjacent buildings/structures.
The Open Spaces were checked using WorldView-3 (2017, NAMRIA), WorldView-4 (2018, DOST-ASTI) and Google recent imagery.
The buildings were generated using the LiDAR Digital Terrain Model (DTM) and Digital Surface Model (DSM). The buildings were buffered by its height multiplied by 1.5. The buffered buildings were overlaid to Land Use, and the Open Spaces were determined outside the buffered areas.
The Open Spaces with areas minimum of 200 sqm were extracted and checked with the recent imageries. The Open Spaces were assessed by PHIVOLCS from Earthquake-related hazards such as not transected by the Valley Fault System, no Tsunami, no Liquefaction and no Earthquake-Induced Landslides. The remaining open spaces without the said hazards are identified as the Safe Open Spaces (SOS).
The SOS were categorized according to area: Small (200 - 500 sqm), Medium (>500 - 5,000 sqm) and Large (> 5,000 sqm). The SOS were also divided into 4 quadrants: North, South, East and West, taking into considerations a scenario predicted by the MMEIRS study which indicates that Metro Manila could be split into 4 parts due to collapses of main bridges and liquefaction hazards. The ground validations of SOS were conducted in 2019 by the concerned local government units of Metro Manila with the technical assistance of NAMRIA. The LGUs validation activity was monitored by the DILG-NCR.
Depending on the basemaps used and methods employed during mapping, discrepancies may be observed between location of hazards or exposure information and actual ground observations.
For areas transected or are within 300 meters from active faults, we recommend that you refer to the Active Fault maps generated by DOST-PHIVOLCS.
Volcanic fissures identified are based on results from preliminary field investigations. Hazard assessment may change, depending on results of final mapping and analysis conducted by DOST-PHIVOLCS scientists.
Fissures may develop further if the condition that generated them persists, as a response to geological processes. For land-use planning and disaster risk reduction purposes, at least 5 meters on both sides of the fissure or at the edge of the deformation zone may be considered as a Zone of Avoidance.
Stakeholders are advised to report to the Institute any fissures that may be observed in the project site since fissure mapping is still ongoing as this may change the assessment.
The Flood Impact Maps by DOST-ASTI were identified via Artificial Intelligence from a composite of three (3) Sentinel-1 SAR images. Please note that these have not been validated on the ground and the thematic accuracy might be lower in urban and forested areas due to inherent limitations of the SAR data and processing used. Please refer to this paper to know more about the methodology.
To optimize the use of this information in HazardHunterPH, DENR-MGB’s Flood Susceptibility information (violet shades) is displayed vis-a-vis DOST-ASTI's AI-generated flood information (red). The user may change basemaps to highlight areas and features of interest.