Inaccurate rain forecast contributed to high 'Usman' fatalities, says geologist

Filipino geologist Mahar Lagmay, in his analysis on the effects of Tropical Depression Usman that claimed over a hundred lives, cited inaccurate rain forecast as a contributing factor.

"Ang forecast noong December 28-29, 2018 ay moderate (light blue) to heavy (dark blue) rainfall sa Bicol... Ang totoong nangyari ay intense (yellow) to torrential (red) ang pinakamalalakas na ulan," Lagmay said in a Facebook post on Saturday.

He pointed out that these rainfall levels vary significantly with moderate rain measuring 2.5-7.5 mm per hour; heavy rain equal to 7.5-15 mm per hour; intense rain amounting to 15-30 mm per hour; and torrential rain bringing about more than 30 mm per hour.

"Tumagal ng ilang mga oras ang intense at torrential rainfall sa Bicol," he said.

Lagmay also said the affected residents were caught off-guard because based on the forecast, Usman's landfall is expected to take place on December 29.

"As early as in the morning of Dec 28 ay bumabakbak na ang intense at torrential rain sa Bicol. Huli na ang lahat ng malaman ng mga tao na kinailangan ng sapat na action," he said.

Another factor he inferred was that the public did not expect TD Usman to bring so much rain as only Signal No. 1 was raised in the affected areas.

"Wala pong kinalaman ang signal number sa dami ng ulan dahil ang signal numbers ng PAGASA ay lakas ng hangin ang basehan," Lagmay said.

GMA News Online is trying to reach PAGASA for comment about Lagmay's analysis but has yet to receive a response as of posting time.

Hazard mapping

The geologist said that aside from weather forecasts, community knowledge on the hazardous and safe places in their areas is equally important.

Lagmay cited data from the Mines and Geosciences Bureau showing that some Usman-hit areas in Bicol were susceptible to landslides.

He mentioned that the disaster risk reduction and management program Project NOAH has created hazard maps from 2012 to mid-2017, which were intended for the local governments' use in planning where to put evacuation sites.

"Ang objective ng hazard mapping ay hindi para maipakita lamang ang hazards. Ang totoong layunin ng hazard mapping ay maipakita ang mga pinakaligtas na lugar sa isang komunidad gamit ang siyensiya sa pag-intindi ng hazards," he said.

Lagmay was the executive director of Project NOAH (Nationwide Operational Assessment of Hazards) that was shut down by the government last March 2017. — BAP, GMA News