The water resources of the islands composing the 32 atolls of the Federated States of Micronesia (FSM) are under continual threat due to El Niño-induced drought events and potential sea-level rise. With current government policies encouraging the sustainability of atoll island communities, accurate and efficient methods to estimate the water resources of atoll islands of the FSM are of critical need. Of prime importance is an estimation of groundwater resources, which the communities are dependent upon for sustainability during prolonged drought events.

Due to the sparseness of actual hydrologic data and the exorbitant cost of procuring data sets required for hydrologic trend analysis, we present the use of a recently-developed algebraic model, based on numerical modeling results of atoll island hydrogeology, to estimate groundwater resources of atoll islands. Specifically, the model provides estimates of the freshwater lens thickness during normal and drought-induced climatic conditions. The model is validated for use in the FSM under average climatic conditions through comparison of model results with the available data regarding the freshwater lens thickness on several atolls in the FSM, and validated for use under El Niño-induced conditions through comparison of model results with freshwater lens data gathered during the 1998 drought on Majuro Atoll, which experiences a climate similar to the FSM.

The model is then applied to each atoll island within the FSM, to determine the freshwater lens thickness to be expected during both average and drought-induced hydrologic conditions. Results indicate that of the 105 atoll islands considered only 6 would retain a fresh body of groundwater able to sustain the community during a drought similar to that experienced in 1998. In general, results can provide water resources managers and policy makers with important information regarding the sustainability of atoll island communities.