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Water Resources on Guam: Potential Impacts and Adaptive Response to Climate Change for U.S. Department of Defense Installations

Project Chief: Stephen B. Gingerich
Project Period: October 2013 through September 2017
Cooperator: U.S. Department of Defense Strategic Environmental Research and Development Program
Location: Island of Guam


The U.S. Department of Defense (DoD) relies on surface water and groundwater for operations at its installations on Guam. Water demands are projected to increase and the effects of climate change may limit the water resources available to meet these demands.

On Guam, the Fena Valley Reservoir, located in south-central Guam, is an important water supply for the U.S. Navy and many citizens on Guam. The USGS uses a calibrated PRMS watershed model of the Fena Valley Watershed and a water-balance model of the Fena Valley Reservoir to provide 6-month forecasts of water availability for the reservoir. Estimates of future runoff, generated from the watershed model, are needed for the water-balance model. Sediment carried by runoff into the reservoir reduces the storage capacity of the reservoir. Sediment also causes turbidity that must be treated before distribution of the water.

In northern Guam, the groundwater system consists of a lens-shaped freshwater body, an intermediate, thin transition zone of brackish water, and underlying saltwater. Recharge to the freshwater-lens system is from infiltration of rainfall. Groundwater recharge was estimated from mass-balance water-accounting budgets. Groundwater wells, where freshwater is underlain by saltwater, are highly susceptible to saltwater intrusion. The effects of changing recharge and sea-level rise on Guam’s freshwater lens will be evaluated in this study using a groundwater numerical model. As sea level rises, the freshwater lens will also rise, bringing brackish water higher and closer to the pump intakes in the production wells.


This four-year study evaluates potential adverse climate-change impacts on U.S. DoD installations which rely on Guam’s surface-water and groundwater resources. For a range of climate-change scenarios on Guam, the study will:

  • evaluate how streamflow, sediment loads, and turbidity will be modified and affect surface-water availability
  • assess how groundwater recharge and salinity will be modified
  • define impacts to DoD infrastructure supplying surface water and groundwater and highlight adaptive strategies to maximize the water resources
  • evaluate and implement effective communication strategies to inform water managers about potential impacts and adaptive strategies

Relevance and Benefits

The results from this study are necessary for the proper management of the water resources on Guam. The study is consistent with the USGS Science Strategy to provide citizens, communities, natural-resource managers, and policymakers with a clearer knowledge of the status of their water resources. Information generated by this study will yield immediate practical benefits to the U.S. DoD by characterizing the efficacy of different management strategies and adaptations to projected climate change on Guam.


To meet the objectives of this study, the research team will (1) develop regional and local climate projections; (2) develop a southern Guam watershed model; (3) recalculate Fena Valley Reservoir capacity; (4) investigate groundwater geochemistry and refine recharge estimates; (5) apply the northern Guam groundwater model; (6) assess adaptive strategies; and (7) communicate the results. Results from this study will be published in the USGS Scientific Investigations Report series and made available on the internet, and in scientific journals.

Scientific Collaboration (Research Team)

  • U.S. Geological Survey (USGS)
      Stephen Gingerich, Principal Investigator
      Delwyn Oki
  • University of Guam, Water and Environmental Research Institute of the Western Pacific (WERI)
      John Jenson
      Mark Lander
  • University of Texas at Austin, Jackson School of Geosciences (UTA)
      Jay Banner
  • University of Hawaii at Manoa, International Pacific Research Center (IPRC)
      Annamalai Hariharasubramanian
      Yuqing Wang
  • East-West Center (EWC)
      Melissa Finucane
      Victoria Keener

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