By Purple S. Romero
MANILA (AlertNet)- As tropical storm Ketsana pummeled the Philippines on September 26, 2009, geologist Alfredo Mahar Lagmay collected information on flood-affected areas through Facebook, a social networking site.
"I first asked my friends from Facebook to describe their situation Â? how high the water level was in their areas. Then I went on news programs and called on others to provide me with data," remembers the professor at the University of the Philippines' National Institute of Geological Studies.
Lagmay used each response he received to plot points in Google Maps, a web mapping service, to identify the spots around the city that already were submerged.
A week later, around 1,000 "netizens," or users of online sites, who resided in different parts of metropolitan Manila, contributed additional data to the map.
The information has shaped the Typhoon Ondoy Maximum Flood Height map
a tool which now informs Manila residents about how vulnerable their respective areas are to flooding.
Ondoy is a local Philippines term for Ketsana.
MAP A'CITIZEN-BASED' RESOURCE
Because the map was formed through public efforts, Lagmay refers to it as a "citizen-based" resource. Free and easily accessible, it is now considered a key tool for disaster risk reduction efforts in Manila by everyone from urban planners to motorists trying to avoid flooded roads during typhoons.
On the map, flood height is indicated by pins of different colors and can be easily understood, as the risk level is based on how high it would reach on the body of someone of typical height in the Philippines.
Light blue means the flood is ankle high, yellow is knee high, green is neck high, violet is top-of-the-head high, dotted aqua is one story high and dotted pink is one and a half stories high.
The map focuses in particular detail on Marikina and Antipolo, areas of Manila which were badly flooded by the tropical storm. Residents there, who have contributed data to the maps, described water levels in parts of Marikina as two stories high, while some areas in Antipolo were hit by six feet of flood water.
To supplement the citizen data reports, Lagmay turned to rainfall data from the Manila Observatory, a non-profit research institute that does atmospheric science research, and the Philippine Atmospheric, Geophysical and Astronomical Services Administration.
From the two institutions, Lagmay learned that tropical storm Ketsana poured 400 millimeters of rain water onto the country in a matter of hours, a deluge that helps explain why rivers rose so quickly and their waters rapidly spread.
Lagmay also examined satellite weather images and radar images taken during the storm's onslaught and provided by the Japan Aerospace Exploration Agency and the Ministry of Economy, Trade and Industry. And he carried out statistical analysis to identify the margin of error in his map.
To produce the map itself, he sought the assistance of experts working in the volcano tectonics laboratory of the National Institute of Geological Sciences.
The map, a remarkable collaborative effort, will not only help citizens avoid areas vulnerable to the worst flooding during storms, but should help the government ascertain where rescue teams and other disaster resources are most needed.
WHERE TO DEPLOY RESOURCES FIRST
This function is crucial because the government has limited equipment. From the map, for instance, the National Disaster Coordinating Council could quickly decide where to send its rubber rescue boats first.
The map also aids both scientists and public officials in tracing the sources of flooding, and may help overturn established ideas about where flood waters originate and how they move. Urban planners could also use the data to assess the level of disaster risk in various areas in the metropolis.
Lagmay now aims to produce a flood hazard map for the whole country, but is struggling to get sufficient data and the kind of strong public participation he had as Ketsana raged.
The new map "suffers from such limitations," he said. Even in metropolitan Manila, not all areas are depicted on the flood map as citizen reports were scarce in some areas.
But "we have to work with what we have," he said. By promoting the project, Lagmay hopes to generate a new wave of public support for the effort Â? before the floods come rushing in again.
Purple S. Romero is a researcher-writer with Newsbreak, a Philippines-based independent news organization.
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