Rainfall and Land Cover Changes Impact on the Hydrologic Responses of Santa Cruz Watershed, Laguna, Philippines

Watershed provides a wide range of ecosystem services. Part of its provisioning services is the quantity, distribution, and timing of water supply. The state of water resources is affected, among others, by rainfall and land use and land cover (LULC) changes. With the Philippines consistently ranking very high in the World Risk Index reports in terms of disaster risks and land use intensification due to continuous growth in population and economic activities; it is crucial and timely to conduct research in relation to its hydrological impacts. This study aimed to detect and project the separate and combined impacts of these changes on the surface runoff responses of Santa Cruz Watershed during a typhoon event using the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) model. The study was able to identify, and bias-corrected five General Circulation Models (GCM) under Representative Concentration Pathways (RCP) 4.5 and 8.5 storylines to account for the future impact of change in rainfall. Meanwhile, LULC modeling was executed using the Markov chain method to project its 2040 state. Combined impacts revealed a certainty that peak discharge and total volume will increase, and the time of peak will be earlier than the baseline model for both RCP 4.5 and 8.5 scenarios. The output of the study can serve as a vital input in crafting evidence-based policy and decision-making in relation to watershed planning and management.