Hydrological modelling for Panay and Pampanga, Philippines 1979 - 2089

Scheidegger, Johanna M.; Jackson, Christopher R.; Barkwith, Andrew; Wang, Lei; Guzman, Maria Aileen Leah G.. 2022 Hydrological modelling for Panay and Pampanga, Philippines 1979 - 2089. Nottingham, UK, British Geological Survey, 71pp. (OR/22/057) (Unpublished)

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Abstract/Summary

This report describes an investigation of the impact of climate change on the hydrological cycle in Panay Island and Pampanga Province, Philippines. We developed an integrated surface water-groundwater model using a version of the widely applied VIC hydrological model that includes a 2D groundwater model: VIC-AMBHAS. The model simulates components of the hydrological cycle, such as soil moisture, evapotranspiration, surface runoff, groundwater recharge, and river baseflow. The model can be used to simulate the hydrological cycle over historical and future time periods. We used data available at a global scale to parameterise the models, which were constructed on a ~1km grid. The meteorological driving data is downscaled to this resolution. Both historical climatology (1979-2018) and future climate projections up to 2089 are used to drive the model to study the impact of climate change on the hydrological cycle. Over the historical period, Pampanga receives marginally more rainfall (181 mm/month) than Panay (174 mm/month). However, the partitioning of precipitation into the different water fluxes varies for the two regions. In Panay, 72% of the precipitation is partitioned into evapotranspiration whereas in Pampanga this is only 60% of the precipitation. This results in higher surface runoff and groundwater recharge in Pampanga (runoff: 44 mm/month, recharge: 36 mm/month) than Panay (runoff: 33 mm/month, recharge: 18 mm/month). Consequently, on an annual basis, Panay receives half the groundwater recharge compared to Pampanga. We apply projections of future climate derived from global climate simulations undertaken by the UK Meteorological Office’s Hadley Centre – the UKCP18 projections. We also apply two sets of UKCP18 projections that consider different greenhouse gas concentration pathways: RCP2.6 and RCP8.5. In RCP 2.6 carbon dioxide emissions start declining by 2020 and go to zero by 2100. In RCP 8.5 emissions continue to rise throughout the 21st century. Simulated hydrological changes produced using the RCP2.6 and RCP8.5 projections for the 2050s (Table 1) are relatively similar for each location and indicate the following: • Panay: o Reduction in precipitation of 5% o Reduction in groundwater recharge of 11-12% o Reduction in surface runoff of 6% o Reduction in river baseflow of 12-13% • Pampanga o No change in precipitation o Reduction in groundwater recharge of 2-4% o No clear change in surface runoff o Reduction in river baseflow of 1-3% Simulated hydrological changes for 2080s (Table 2) are in less agreement between the RCP2.6 and RCP8.5 than the 2050s: • Panay: o Reduction in precipitation of 6-15% o Reduction in groundwater recharge 13-29% o Reduction in surface runoff 6-17% o Reduction in river baseflow 15-33% • Pampanga o Reduction in precipitation of 2-4% o Reduction in groundwater recharge 4-12% o Reduction in surface runoff 3-4% o Reduction in river baseflow 3-9% The model simulations highlight regional differences in the groundwater and surface water availability for Panay and Pampanga for both the historical and future climate periods. Panay receives less groundwater recharge and is projected to be more affected by impacts of climate change than Pampanga. The effects of climate change will result in a larger reduction in precipitation, groundwater, and surface water for periods later in the century. Whilst the VIC-AMBHAS model has been applied to Pampanga and Panay, an associated modelling framework has been developed which supports the application of the model to other Philippine islands or to the whole of the Philippines. For example, this framework facilitates the processing and downscaling of global climate datasets to create the related input files required by the model. Following on from this project, the British Geological Survey are extending this work by developing a national-scale hydrological model for the whole of the Philippines. This national model will seek to inform the water resource sector and policy makers about regional differences in water availability and predicted response to climate change to help with decision making and policy development.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Additional Keywords:	GroundwaterBGS, Groundwater
Date made live:	15 Nov 2022 10:44 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/533547

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