The concept of smallness, for the purposes of this study, is
largely based on hydrological characteristics. From a hydrological perspective,
a small island can be considered to be one on which water resources are very
scarce and where special measures often need to be adopted to develop and manage
such resources as may be available. These special measures typically go beyond
those normally considered as standard practice on large islands or continents.
Various definitions of small islands have been adopted. In 1991,
UNESCO adopted 2 000 km2 as the areal limit for a "small island".
Their definition also included islands where the width did not exceed 10 km.
UNESCO also recognised the concept of a "very small island" where the problem of
water resource scarcity was even more acute and where surface water resources
were normally absent. Very small islands were defined as ones where the area did
not exceed 100 km2 or the width was not greater than 3 km. In such
islands, groundwater was normally the only naturally occurring source of water.
Some very small islands have unfavourable geological conditions for the
formation of freshwater lenses (groundwater) and the only option for
conventional water resources development may be rainwater harvesting. For the
purposes of this study, a small island means all islands less than 2 000
km2 in areal extent, but with special consideration given to the very
small island category (defined as islands with areas not greater than 100