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.