In recent years, flooding has emerged as a persistent and increasingly severe concern in many regions of the Philippines, with urbanization recognized as one of its major contributing factors. As built-up areas expand, the alteration of natural land cover significantly modifies watershed processes, often intensifying surface runoff and peak flows during extreme rainfall events. This study aims to determine how Land Use and Land Cover Change influence the hydrologic behavior of the Hijo River Basin (Figure 1)—a rapidly urbanizing watershed. By applying the Hydrologic Engineering Center's Hydrologic Modeling System (HEC-HMS), the research isolates the impact of Land Use and Land Cover Change changes by holding rainfall inputs constant across all scenarios. The output of the study is a comparative analysis of generated hydrographs, hyetographs, and peak discharge values. The results are expected to support more informed watershed management, urban planning, and flood mitigation efforts in the region.

Water is one of the most vital resources, used in agriculture, tourism, and energy, and by humans and biodiversity. The Loboc River Basin (Figure 3) is also used in the same way, providing water to its surrounding municipalities in Bohol, Philippines. However, watershed hydrology is threatened by climate change and land use/land cover change in which it can degrade water quality and lessen water availability. Therefore, this study aims to simulate the hydrological processes of the Loboc River Basin for the baseline (2000-2020), 2030, and 2050 in basin and subbasin scale with climate change projections and land use/land cover change scenarios, and to quantify and evaluate the projected changes in surface runoff, lateral flow, groundwater flow, evapotranspiration, and streamflow. This will be achieved through data processing and modeling in the open-source Geographic Information System (QGIS) using the the Soil and Water Assessment Tool (QSWAT) plug-in utilizing climate data from the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) and land use data from the National Mapping and Resource Information Authority (NAMRIA). Model calibration will be done under SWAT-CUP (Soil and Water Assessment Tool - Calibration and Uncertainty Program) using observed streamflow data from the Department of Public Works and Highways (DPWH). The findings are expected to reveal the hydrological response of the Loboc River Basin to scenarios under climate change-only, land use/land cover change only, and combined, and provide valuable insight into the application of the Soil and Water Assessment Tool SWAT in medium-scale basin and in a tropical climate specifically type IV climate based on the Modified Coronas Classification.

Blue-Green Infrastructures (BGIs) are interconnected networks of natural and artificial structures designed for efficient water management, along with other roles such as urban cooling and flood mitigation, with marginal side effects. Blue-Green Infrastructures are praised for being climate-resilient infrastructures, which are especially warranted in the Philippines, whose geographic location, compounded by climate change, increases its exposure to extreme weather events. This study aims to evaluate the performance of Blue-Green Infrastructures as flood mitigation measures in the Sta. Cruz River Basin (Figure 5), a subbasin of the greater Pasig-Marikina-Laguna de Bay Basin. A geospatial and socio-economic approach will be utilized to identify potential locations for the implementation of Blue-Green Infrastructures in the watershed, while their performance will be evaluated using the Soil Water Assessment Tool (SWAT) Model on a ten-year climate and land use projection. The study is expected to yield the following outputs: (1) a map showing the suitability of Blue-Green Infrastructures in the area; (2) a calibrated model displaying the surface runoff in the basin with and without the implementation of Blue-Green Infrastructures; and (3) a criteria for choosing the most appropriate Blue-Green Infrastructure component in the watershed.