A total of 664 barangays across Luzon, including 412 in Metro Manila, are at risk of rain-induced floods, landslides, flash floods, and debris flow from July 3 to 6, the Department of Environment and Natural Resources – Mines and Geosciences Bureau (DENR-MGB) reported on Thursday, July 3.

The warning is based on the bureau’s Geohazard Advisory No. 1, which was issued in connection with the prevailing effects of a low-pressure area (LPA) and the southwest monsoon or habagat. 

According to the DENR-MGB, the figures were derived from forecasted rainfall accumulation thresholds under the agency’s Hazard Mapping and Assessment for Effective Community-Based Disaster Risk Management (READY) program.

“It is advised that all Local Government Units (P/C/MLGUs), P/C/M/B Disaster Risk Reduction and Management Councils (P/C/M/BDRRMCs), as well as the communities to remain vigilant for possible occurrence of landslides, flood/flash flood and or debris flow in their respective Areas of Responsibility,” the agency said.

In the National Capital Region (NCR), 412 barangays have been identified as at risk. 

These include 117 barangays in the City of Manila, 114 in Quezon City, 16 in Marikina, one in Pasig, and a combined 164 in the cities of Caloocan, Malabon, Navotas, and Valenzuela, which make up the region’s third legislative district.

“The threshold values were lowered in Metro Manila due to the nature of flooding in highly urbanized areas, wherein the rains are not readily absorbed by the land. This leads to increased surface runoff that overwhelms the drainage system and causes flooding in low-lying areas, as well as those proximal to waterways,” the bureau explained.

In Northern and Central Luzon, 252 barangays were also flagged as vulnerable. 

In Cagayan Valley, 118 barangays in Cagayan province and 105 in Isabela were listed. 

Meanwhile, in Central Luzon, 81 barangays in Zambales and 36 in Bataan were included. 

The Cordillera Administrative Region had two barangays each in Apayao and Kalinga, while Ilocos Sur had 25.

The agency emphasized that while not all areas forecasted to receive heavy rainfall by PAGASA are included in the geohazard list, they are still advised to prepare and stay alert. 

“Although some provinces mentioned in DOST-PAGASA advisories to be affected by are not included in the current list, they are still advised to activate the appropriate preparedness measures and monitor for future geohazard advisories, should there be any sudden changes in the rainfall forecast or weather conditions,” the MGB noted.

The MGB also urged local government units to implement pre-emptive measures depending on their area’s susceptibility level. 

For moderately susceptible areas, the deployment of disaster risk reduction personnel to monitor river levels was recommended, as well as evacuation protocols once water levels reach half a meter. 

Households near riverbanks should also be monitored closely due to erosion risks.

For areas with high to very high susceptibility, the bureau said LGUs must enforce pre-emptive evacuations, clear river channels of obstructions, and restrict access to zones with a history of flash floods.