Study: Over 80% of upper Marikina watershed vulnerable to landslides

MANILA, Philippines — Slope is the biggest contributor to landslide susceptibility in the Upper Marikina River Basin Protected Landscape (UMRBPL), a 2026 study revealed, highlighting the need for stronger preventive measures.

Earlier this month, a landslide hit Baras, Rizal, covering 50 meters of Marilaque Highway and temporarily blocking almost four kilometers of the road, Masungi Georeserve said on Facebook, pointing out the landscape’s susceptibility to landslides.

Based on the study, “GIS-Based Landslide Susceptibility Assessment of the UMRBPL, Rizal, Philippines,” which used the Analytic Hierarchy Process, slope accounted for 28.04% of the area’s landslide susceptibility, the highest contribution among the factors examined.

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Land use and land cover came next at 20.50%, while average annual rainfall accounted for 20.08%.

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The other identified factors were soil morphology, 8.46%; typhoon frequency, 8.08%; distance to lineament, 7.74%; and soil geology, 7.10%.

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“Landslides remind us that a watershed is more than its rivers. Its forests, slopes, soils, roads, and communities are all connected,” said the foundation conserving parts of the more than 26,000-hectare protected landscape.

The assessment showed that almost half of the UMRBPL, or 46.39% of its area, was highly susceptible to landslides, while another 1.80% was classified as having very high susceptibility. Some 38.05% was moderately susceptible.

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Only 12.76% of the area was classified as having low susceptibility, while 1% was found to have very low susceptibility.

As Masungi Georeserve said, the results indicate that eight in 10 hectares of the watershed are “at risk [to landslides].”

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“With land use driving over a fifth of the region’s vulnerability, human impact is undeniable,” it said, pointing to land use and land cover as contributing 20.05% to landslide susceptibility.

“Deforestation and altered soils directly influence how violently the landscape reacts to the next typhoon,” Masungi Georeserve said. /dm