Statistical downscaling method to determine the Antamok Watershed hydrological response to climate change scenario

Abstract The Philippines is known as susceptible to extreme climate changes. Precipitation is one of the major factors that impacts the livelihood of the Filipinos due to the constant flood incidents during extreme Typhoons. Using the three global climate model used from the CMIP6 models of the recent Sixth Assessment Report of the Intergovernmental Panel on Climate Change, the Antamok Watershed projected an increase in monthly precipitation of 227.1% during the dry season under SSP2-4.5 scenario of CanESM5 model. Temperature could also reach a projected increase of 1.5 °C by the end of year 2055. The said watershed may also experience total of 78 future extreme precipitation cases (rainfall amount greater than 300 mm, PAG ASA) projected from 2026 to 2055 (NorESM2-MM) under the SSP5-8.5 scenario. NorESM2-MM model also produced peak discharges (may reach up to a monthly mean of 765.3 m 3 /s, August) way beyond the validation period and will have percentage increase range of 30.7% (December) to 51.2% (August) both under the SSP1-2.6 scenario. With the simulation of river flow from the observation data, the highest recorded precipitation, 1085.8 mm for 24-hours have registered a maximum of 1014.2 m 3 /s flow in Outlet1 of the HMS model. Comparing it to the projected precipitation, it is expected that the flow might reach up to 1100 m 3 /s between the period of 2045-2050.