Multi-source validation of ecological sensitivity in the Toraja Highlands, South Sulawesi, Indonesia

The Toraja Highlands, encompassing Tana Toraja and North Toraja, form the strategic upper reaches of the Saddang Watershed in South Sulawesi, where steep terrain, active land-cover change, and high ecological sensitivity converge. This study addresses the need for an objective and validated ecological sensitivity map to support sustainable mountain watershed management. We construct an ecological sensitivity index based on principal component analysis using four key indicators: land cover, vegetation density (NDVI), slope, and rainfall, and evaluate its reliability through multi-source validation. Inputs integrate national elevation models, Landsat 8 imagery, and satellite-derived rainfall. Rainfall represents a multi-year climatology for 2015–2024, whereas land cover and NDVI reflect recent surface conditions derived from a cloud-free 2024 composite. The resulting sensitivity zonation indicates that 41.10% of Tana Toraja and 67.11% of North Toraja fall into the very high sensitivity class, concentrated on steep slopes and intensively converted landscapes. Event-based spatial cross-validation against independent landslide records yields overall accuracies of 67.65% and 66.67%, while field verification produces Kappa values of 0.847 and 0.871. Stakeholder appraisal further corroborates the mapped patterns. Together, these convergent lines of evidence identify priority areas for reforestation, soil conservation, slope stabilization, and sustainable watershed management. The transparent and reproducible workflow supports evidence-based risk reduction and resilience building in the upper reaches of the Saddang Watershed.