Climatic and human influences on groundwater in Low Atolls

White Ian M., Falkland Tony, Metutera Taboia, Metai Eita, Overmars Marc, Perez Pascal, Dray Anne. 2007. Climatic and human influences on groundwater in Low Atolls. Vadose zone Journal, 6 (3) : 581-590. International Conference on Groundwater Resources Assesment under the Presures of Humanity and Climate Change, Kyoto, Japon, 4 Avril 2006/6 Avril 2006.

Résumé : Population centers in low, small islands have water supply problems that are among the most critical in the world. Limited land areas and extremely large soil hydraulic conductivities severely reduce surface runoff and surface storage, so that thin lenses of fresh groundwater floating over seawater comprise the major source of fresh water for people in many atolls. Atoll groundwater is extremely vulnerable to frequent El Niño Southern Oscillation (ENSO)-related droughts, salinization due to storm surges and sea-level rise, and to human activities with vadose zone transit times from surface to shallow groundwater being less than 1 h. We examine the relationship between groundwater, rainfall, and ENSO events in a low atoll, Tarawa, in the central and western Pacific Republic of Kiribati. Droughts can last as long as 43 months and occur with a current frequency of 6 to 7 years. The impact of droughts on the quality and quantity of a fresh groundwater lens is explored. The local drawdown of the water table due to pumping from long horizontal infiltration galleries is found to be less than diurnal tidal variations. The saturated hydraulic conductivity, K0, of the Holocene unconsolidated coral sands was estimated from infiltration gallery drawdown in two islands. The geometric mean K0 was 14.6 m d-1 with a range from 0.9 to 111 m d-1. These large K0 values cause the rapid transmission of rainfall and surface pollutants through the unsaturated zone to groundwater. An example is given of Escherichia coli pollution due to traditional activities. Strategies for improving the adaptation of island communities and increasing resilience to climate change are discussed.

Mots-clés Agrovoc : atoll, eau souterraine, approvisionnement en eau, qualité de l'eau, conservation de l'eau, facteur climatique, impact sur l'environnement, eau douce

Mots-clés géographiques Agrovoc : Kiribati

Classification Agris : P10 - Ressources en eau et leur gestion

Champ stratégique Cirad : Axe 6 (2005-2013) - Agriculture, environnement, nature et sociétés

Auteurs et affiliations

• White Ian M., ANU (AUS)
• Falkland Tony, Ecowise Environmental (AUS)
• Metutera Taboia, Kiribati (KIR)
• Metai Eita, Kiribati (KIR)
• Overmars Marc, South Pacific Applied Geoscience Commission (FJI)
• Perez Pascal, CIRAD-ES-UMR G-EAU (AUS)
• Dray Anne, ANU (AUS)

Source : Cirad - Agritrop (https://agritrop.cirad.fr/543714/)

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