TY  - EJOU
AU  - Alejo, Lanie A. 
AU  - Balderama, Orlando F. 
AU  - Cruz, Rex Victor O. 

TI  - Integrated Assessment of Hydrologic Response and Spatial Hazard Vulnerability for Tropical Watershed Management
T2  - Revue Internationale de Géomatique

PY  - 2026
VL  - 35
IS  - 1
SN  - 2116-7060

AB  - The Abuan Watershed in Isabela, Philippines faces increasing hydrologic and environmental pressures from rainfall variability, land-use change, and hazard-sensitive landscape conditions. This study integrated Soil and Water Assessment Tool (SWAT) modeling with GIS-based vulnerability assessment to evaluate watershed response and spatial vulnerability to flood, drought, and soil erosion. A 5 m × 5 m IFSAR-derived digital elevation model, land-use/land-cover data, soil maps, and hydroclimatic and streamflow records supported the analysis. Streamflow performance was acceptable, with calibration values of R<sup>2</sup> = 0.61, nRMSE = 22%, and PBIAS = 3.1%, and validation values of R<sup>2</sup> = 0.70, nRMSE = 14%, and PBIAS = 10%. Under baseline conditions, the 63,922-ha watershed received 2169.1 mm of annual precipitation, of which 47% became surface runoff, 23% evapotranspiration, and 30% percolation. Wetter scenarios produced the clearest hydrologic response, increasing runoff by up to 15.99% and soil erosion by up to 13.02% under combined land-use and rainfall-change conditions. Under the projected 2050 rainfall scenario, reforestation caused only minor runoff and percolation changes but reduced simulated soil erosion by up to 1.16 t ha<sup>−1</sup> yr<sup>−1</sup> relative to the urbanized condition. Flood vulnerability was concentrated in downstream agricultural and settlement areas, whereas drought and soil-erosion vulnerability were greater in cultivated and rainfed uplands. Priority actions therefore include flood-risk reduction and runoff moderation in downstream lowlands, together with vegetation recovery, reforestation, and soil-conservation measures in cultivated hilly and rolling terrain. The integrated SWAT–GIS approach provides a practical, spatially explicit basis for watershed prioritization and intervention planning for future watershed management.
KW  - Hydrologic modeling; GIS-based vulnerability assessment; flood vulnerability; drought vulnerability; soil erosion; watershed management; land-use change; climate variability; Abuan Watershed; Philippines

DO  - 10.32604/rig.2026.084091