CLIMATE CHANGE EFFECT ON DISCHARGE AND LAKE LEVEL OF PASIG-MARIKINA RIVER AND LAGUNA LAKE BASIN USING DYNAMICALLY DOWNSCALED MRI-AGCM 3.2S GLOBAL CLIMATE MODEL OUTPUT IN A HYDROLOGICAL MODEL

Abstract

Climate change impacts discharge patterns and water levels globally, including the vital Pasig-Marikina River and Laguna Lake Basin in the Philippines. Using dynamically downscaled and bias-corrected outputs from the MRI-AGCM 3.2S global climate model, input-forced into the WEB-RRI hydrological model, we assess projected changes. These findings provide guidance for policymakers, water managers, and researchers in developing climate-resilient strategies. Future scenarios (RCP 8.5) reveal significant increases in maximum daily lake discharge, reaching over 1,000 m³/s, and a shift in maximum mean monthly discharge from August to July. Flood frequency nearly triples, the maximum lake level increases by 2.05 m, while the maximum inundation extent expands, affecting an additional 83 km². This study underscores the basin’s vulnerability to climate change, highlighting the urgent need for adaptive water management strategies.