Modeling the Hydrologic Responses to Land Cover and Climate Changes of Selected Watersheds in the Philippines Using Soil and Water Assessment Tool (SWAT) Model

Quantitative prediction of land cover and climate change impacts on hydrologic processes is widely used to develop sound watershed management strategies. However, not much is yet understood about the hydrologic behavior of watersheds in the Philippines in response to land cover change and climate variability. This study was designed to simulate the hydrologic responses of eight land cover and climate scenarios of Pagsanjan-Lumban Watershed (PLW) in Laguna, Quiaoit River Watershed (QRW) in Ilocos Norte, and Saug Watershed (SW) in Davao del Norte through the Soil and Water Assessment Tool (SWAT). Streamflow was then used to calibrate and validate the model using SUFI-2 algorithm in SWATCUP. The calibration exhibited a good match between observed and simulated streamflow for PLW (R2 = 0.72, NS = 0.69), QRW (R2 = 0.67, NS = 0.62), and SW (R2 = 0.78 NS = 0.77). Simulation results showed that (i) increased (decreased) precipitation in the areas also increased (decreased) water yield, surface runoff, and baseflow; (ii) the moderate shift to forest within the watershed moderately decreased runoff volume and increased evapotranspiration, which consequently decreased baseflow; (iii) urbanization resulted in lower baseflow but higher evapotranspiration; and (iv) presence of forest vegetation is associated with high infiltration and recharge; thus, lower surface runoff with higher baseflow. Hydrologic behavior, therefore, changes as it responds to changes in land cover and climate. Thus, appropriate interventions are vital to attain water security and sustainability in the watersheds.