'Habagat' prompts warnings on lahar from Taal and Mount Pinatubo, flooding from La Mesa Dam

MANILA — Continuous heavy rainfall driven by the enhanced southwest monsoon (Habagat) has prompted heightened emergency alerts across Luzon. 

Philippine authorities have issued warnings for potential volcanic lahars from Mount Pinatubo and Taal Volcano, overflow flooding from the La Mesa Dam in Metro Manila, and widespread landslides affecting thousands of communities nationwide.

According to the National Disaster Risk Reduction and Management Council (NDRRMC), the weather system—further intensified by recent tropical cyclones—has affected more than 2.3 million families (approximately 8 million individuals) across the country. 

The casualty toll has risen to 32 deaths, 19 injuries, and three individuals reported missing across Quezon City, Manila, and Batangas City.

In an assessment valid from August 29 through September 1, the Mines and Geosciences Bureau (MGB) warned that a total of 8,823 barangays nationwide are highly susceptible to landslides and flooding due to persistent downpours.

The MGB advisory, derived from PAGASA’s 72-hour forecast using Global Spectral Model (GSM) and Weather Research and Forecasting (WRF) 50 millimeter rainfall thresholds, covers high-risk communities across multiple regions:

Northern and Central Luzon: Ilocos Region (Ilocos Norte, Ilocos Sur, La Union, Pangasinan), Cagayan Valley (Cagayan, Isabela, Nueva Vizcaya), the Cordillera Administrative Region (Abra, Apayao, Ifugao, Kalinga, Mountain Province, Benguet), and Central Luzon (Aurora, Bataan, Bulacan, Nueva Ecija, Pampanga, Tarlac, Zambales).

Capital and Southern Luzon: Metro Manila, CALABARZON (Batangas, Cavite, Laguna, Rizal), and MIMAROPA (Occidental Mindoro, Oriental Mindoro).

The Office of Civil Defense (OCD) advised that even unlisted communities situated nearby or downstream from these designated high-risk zones should remain vigilant and prepare for potential secondary impacts.

Volcanic Lahar and Mudflow Advisories

The Philippine Institute of Volcanology and Seismology (Phivolcs) has advised local authorities surrounding Mount Pinatubo and Taal Volcano to execute preemptive safety measures as prolonged rains saturate volcanic slopes.

Mount Pinatubo

Heavy rainfall threatens to mobilize remnant pyroclastic deposits from the 1991 eruption. Channel-confined lahars are anticipated along the upper to middle reaches of the Sto. Tomas–Marella and Bucao River systems, with potential transitions into muddy streamflows and severe downstream flooding. High-risk municipalities in Zambales include:

San Marcelino

San Narciso

San Felipe

Botolan

Similar muddy streamflows may also develop along the O’Donnell and Pasig-Potrero River systems, threatening low-lying agricultural and residential areas across Tarlac and Pampanga.

Taal Volcano

Saturated volcanic ash and loose debris on the western and northern slopes facing Taal Lake present a heightened risk of muddy streamflows, heavy runoff, and debris flows. Communities in Batangas—most notably Agoncillo, Laurel, and Talisay—have been advised to closely monitor local waterways as volcanic materials wash into channels and roadways.

La Mesa Dam Reaches Overflow Elevation

In Metro Manila, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) issued a hydrological warning after the La Mesa Dam in Quezon City exceeded its spill level due to relentless precipitation.

As of 2:00 p.m., the dam’s water level reached 80.22 meters, breaching its spillway threshold of 80.15 meters. Because La Mesa Dam operates without control gates, excess floodwater spills directly into the Tullahan River system.

PAGASA warned that ongoing rainfall over the watershed will cause river levels to surge, urging immediate evacuation preparedness for riverbank and low-lying communities along the drainage pathway:

Quezon City: Fairview, Forest Hills Subdivision, Quirino Highway, Sta. Quiteria, and San Bartolome

Valenzuela City: Vicinity of the North Luzon Expressway (NLEX) and La Huerta Subdivision

Downstream Coastal/Riverine Zones: Low-lying areas along the Tullahan River in Caloocan, Malabon, and Navotas

Phivolcs, PAGASA, and the OCD confirmed they are maintaining round-the-clock monitoring operations while coordinating real-time updates with local government units (LGUs) and national disaster response agencies.

-Paraluman News with reports from the Philippine News Agency