Assessing Groundwater Recharge Under Future Climate Projections and Land-Cover Scenarios Developed through a Participatory Approach, Tutuila, American Samoa

Abstract:

Already changing climates have the potential to significantly impact global water resources availability. On many volcanic islands, groundwater is the primary drinking water source, making well-informed management of this limited resource essential. In this study, we develop high- temporal and spatial resolution groundwater recharge estimates for Tutuila, American Samoa using the Soil Water-Balance-2 model (SWB2). We also assess future change in recharge by incorporating multiple combinations of end-of-century climate scenarios from dynamically downscaled general circulation model predictions, and future land-cover scenarios developed through a participatory approach with local stakeholder groups. Present-day results indicate 57% of Tutuila’s rainfall becomes groundwater recharge, 8% evaporates from the canopy, 15% is evapotranspired, and 19% discharges as stormflow-runoff. Future climate scenarios suggest recharge may increase by 8% or 14% depending on global emissions. Land-cover was a less significant driver of hydrologic change, although increases in impervious surfaces showed a negative impact on recharge. This work is maintained as an active open-source project on GitHub, the world’s leading software development platform, thereby enhancing transparency, reproducibility, and participation from stakeholders and managers in American Samoa. This study is the first of its kind from a location within the South Pacific Convergence Zone, and provides insights into how human activities on global and local levels affect the future sustainability of one our most essential resources.