Hydroclimatic assessment of water resources of low Pacific

For many of the low islands of the tropical Pacific, freshwater is a scarce resource. Water catchment areas
are small and groundwater storage is a shallow fresh water lens. The high hydraulic conductivities of the coral and
sand substrate means surface water is limited. Realization of the possible impact of climate change has highlighted the
sensitivity of island communities to the availability of water. However, impact evaluation requires specialized data as
well as appropriate sensitivity assessment methodologies. This is the second of a two part study. The first addressed the
data problem by assembling and validating a suitable database. The second develops an island water balance model and
applies a sensitivity assessment. Data are at a 2.5◦
×2.5◦ latitude–longitude grid resolution for the Pacific bounded by
coordinates 30◦Sto30◦N and 155◦E to 120◦W. Output is in the form of Climate Change Sensitivity Index maps that show
the impact on the spatial redistribution of climate-determined freshwater resources under various climate scenarios. The
method allows for estimation of water deficits or surpluses for low islands located in any part of the study area. Areas
of high sensitivity to climatic change are those that sit between margins of very wet and very dry zones. Their extent is
determined by the gradients at the margins. Steep gradients define small areas of high sensitivity, whereas gentle gradients
appear as large areas of high sensitivity. Adjustments to the model for differing local surface conditions on different islands
can be easily made, which allows a sensitivity assessment of individual islands, even for islands with no climate station
data. The approach could be a powerful tool to gain useful information on the influence of climate change on freshwater
resources of low islands. Planning decision-making is possible without knowing precisely the magnitude of climate change
that might occur.

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