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Water yield is an important service since it plays a significant role in supporting ecosystems, human livelihood, and economic activities. It is a valuable indicator for understanding the significance of water resources in specific geographic regions. This paper focuses on the valuation of water supply as an ecosystem service in the subwatersheds of the Upper Pampanga River Basin (UPRB) by applying the InVEST model in both scenarios of business-as-usual (BAU) and development. The model incorporates economic valuation techniques, i.e. net present value (NPV), thereby enabling the assessment of the monetary value associated with water supply. The results of this study show that there is a slightly decreasing trend in the annual water yield values in both scenarios. In terms of land area, the largest area under the projected BAU and development scenario (2020-2027) is grassland and forest, respectively. The results provided insights into how land use changes and climate variability affect water yield, with the BAU scenario yielding a total annual water volume of 2.3 billion m³ compared to 2.1 billion m³ in the development scenario. Furthermore, the NPV is estimated at PHP 24.6 billion for the BAU scenario and PHP 22.4 billion for the development scenario. These findings are pivotal for decision-making frameworks, hence underscoring the imperative of sustainable land use practices and water resource management in the UPRB. The study underscores the necessity of conducting a comprehensive assessment of ecosystem services to facilitate a balanced trade-off analysis, particularly at the subwatershed or watershed levels. This approach ensures that all factors influencing water yield and ecosystem health are considered, hence providing valuable insights for informed decision-making and effective resource management in the region. [ABSTRACT FROM AUTHOR]