The Distinctive Hydrology of Tropical Islands
The hydrology of tropical islands differs from that of temperate, continental land areas because of climate and geomorphology. The distinctive hydrologic cycle observed on tropical islands represents a history of orographic effects and thermal radiation on island geology and geometry, combined with the omnipresent influence of the sea.
Climate and geomorphology tend to alter the dimensions of time and space in the study and conceptualization of tropical islands hydrology. Islands and their hydrologic units such as stream basins and aquifers are smaller and have well-defined boundaries; floods and droughts are more frequent but have shorter duration; the time lag between rainfall and flooding is much less; aquifer recharge and discharge respond more immediately to rainfall and drought; rainfall and evapotranspiration are more variable in time and space; and average annual rainfall is more variable areally.
The distinctive hydrologic processes operating in tropical islands may be no more complex than in the temperate continents, but they are certainly less studied and documented. For example, (1) traditional empirical derivation of evapotranspiration from potential evaporation may be invalid in tropical islands; (2) indirect measurement of streamflow has been limited by an absence of hydraulic roughness values for stream channels in steep, tropical areas with banks vegetated with bananas, sugar cane, bamboo, pineapples, or other tropical plants; (3) the universal soil-loss equation may not be applicable in many tropical islands; (4) biological and chemical methodologies traditionally applied to determine sanitary conditions, study contamination, and measure the assimilative capacity of streams may not be applicable in the tropics; and (5) extreme chemical weathering found in the humid tropics is responsible for strong leaching of bedrock, high concentrations of clay in sediment, and high rates of surface denudation, but its effect on the occurrence, availability, and ionic composition of ground water has not been measured.
KeywordsRainfall Intensity Drainage Density Orographic Effect Hydrologic Unit Tropical Island
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