Landslide susceptibility mapping of Pagsanjan-Lumban [Philippines] watershed using GIS [Geographical Information System] and analytical hierarchy process

Landslide is one of the most destructive natural calamities that poses great threat to both human lives and properties especially in developing countries like the Philippines. Due to these reasons, many techniques such as Landslide Susceptibility Mapping (LSM) have been developed to reduce the adverse impacts of such phenomenon. This study was conducted to develop a landslide susceptibility map of the Pagsanjan-Lumban watershed by integrating the Analytical Hierarchy Process (AHP) and Geographic Information System (GIS). The study considered seven factors (elevation, slope, rainfall, soil texture, land cover, fault lines and roads) in generating the susceptibility map. Results from AHP showed that experts from various fields have different perspectives on the level of importance of factors that resulted to the variability in judgments. Among the different factors, slope (23.18%) and rainfall (21.50%) had the highest relative weights while road (8.70%) and elevation (6.61%) had the lowest relative weights. Based on the weighted overlay analysis, the Landslide Susceptibility Index (LSI) of the watershed was observed between 1.43 and 3.65. About 13.82% (6,280 ha) of the area had classification of high susceptibility while 5.51% (2,502 ha) fell under the very high susceptibility level. Furthermore, Lucban (2,648.57 ha) and Lumban (1,956.96 ha) were found to have the largest areas with high to very high susceptibility while Mauban (1.20 ha), Liliw (1.20), Sampaloc (13.49 ha) and Magdalena (28.90 ha) generated low susceptibility levels. The findings of the study can contribute in the effective management of the Pagsanjan-Lumban Watershed.