CITY OF SAN FERNANDO—A group of scientists has expressed concern that many communities in the Philippines remain exposed to potential disasters because they populate areas formed by debris of which the government is not aware.
“It is worrisome that the rapidly growing Philippine population continues to expand into increasingly disaster-prone areas and does so with insufficient hazard evaluation,” according to a geology paper published on Dec. 15.
Backed by Project Noah (Nationwide Operational Assessment of Hazards), a geology team led by Kelvin Rodolfo studied the growth of a village in Compostela Valley that contributed to the disaster caused by Typhoon “Pablo” (international name: “Bopha”) in 2012.
The team concluded that populations have grown on or near many of the 1,200 alluvial fans formed by debris flows.
Alluvial fans are cone-shaped land formations beneath hills and mountains composed of silt, gravel and other forms of sedimentation brought in by water action.
Rodolfo and geologists Mahar Lagmay, Rodrigo Eco, Tatum Miko Herrero, Jerico Mendoza, Likha Minimo and Joy Santiago discussed these conditions in a paper published in the journal “The Natural Hazards and Earth System Sciences.”
“Not all alluvial fans are inhabited but many are. Examples are towns in Aurora,” Lagmay said in an e-mail.
The team also established that climate change has altered the frequency of storms in Mindanao, where communities in danger zones thrived undisturbed until Pablo exposed the dangers in their settlement sites.
The geologists studied population growth of Andap village, New Bataan town, in Compostela Valley in 2012. They described Pablo as abnormal because it formed near the equator and was considered the world’s worst storm in 2012.
Seven hours of rain triggered a debris flow of fast-moving water, rock fragments, soil and mud—equivalent to two million truckloads—into Mayo River, killing 566 people in Andap.
“Debris flows are among the most lethal of natural hazards. They are remarkably poorly recognized in the Philippines, especially in Mindanao, which lies on the southern fringe of the western North Pacific typhoon track and thus has been infrequently visited by typhoons and debris flows,” the scientists said in their paper.
“This unfamiliarity exacerbated the loss of life caused by the Mayo River debris flow,” they said.
The paper suggested that the government “must more rigorously assess the hazards posed to new settlement sites and infrastructure.”
Reviewing US Navy Joint Typhoon Warning Center data going back to 1945, the team learned that storms made landfall in Mindanao only once every 2.5 years.
But that rate abruptly increased to one landfall every 1.32 years from 1990 to 2015.
Another fact causing concern for the team was that Mindanao has, for the first time, suffered cyclones in two consecutive years.
In December 2011, Cagayan de Oro City, 180 kilometers north of New Bataan, received 180 millimeters of rain from Tropical Storm “Sendong” (“Washi”).
Rain fell for six hours, causing floods that killed 1,268 people.
A tropical depression made landfall in Mindanao two months before Sendong, making 2011 the fifth year since 1945 when Mindanao experienced two tropical cyclones.
In 2014, Mindanao again experienced two tropical cyclones: Tropical Depression “Agaton” (“Lingling”) and Tropical Storm “Seniang” (“Jangmi”).
After the Andap disaster, Project Noah inventoried alluvial fans using high-resolution optical satellite imagery. The areas with alluvial fans are found on https://noah.dost.gov.ph. .
They recommended that the best and least costly recourse is for each family to develop its own emergency plans.