Hydrological characteristics

Historically, small islands within a particular region have been divided into hydrological zones on the basis of the major influences on their hydrology. Because of the emphasis on their hydrological characteristics in this process of zonation, the term "hydrological characteristics" has been adopted in this study, small islands with different hydrological characteristics are often found adjacent to each other (e.g., coral islands may occur close to volcanic islands). Such geographic realities defeat the use of the term "zone", which suggests a contiguous area in which a group of islands with basically identical characteristics occur.

The major influences on small island hydrological characteristics, apart from their island status, are climate; physiography (including topography and width); geology and hydrogeology; and, soils and vegetation cover. Other factors which are equally, or sometimes more, important are their relative location to large islands or continents and human-induced impacts. Location can influence the optimal solution for water resources development in some cases; for instance, islands close to continents may find it more economic to "import" water via pipeline from the mainland than to develop onsite technologies. Similarly, human-induced impacts such as mining, deforestation, and urbanisation, may yield both advantages and disadvantages for an island. For example, islands that are set up as tourist resorts or military installations often have economic resources and trained personnel that permit them to consider relatively more expensive and technologically sophisticated options such as desalination. While these islands tend to be special cases, they sometimes occur within SIDS, and, indeed, islands that are set up as tourist resorts generate considerable income for the national economy of such island states.