ABSTRACT
The case within the tropics and is becoming even less common as agricultural, industrial and domestic demands for water supply increase, and as deforestation, land development and possibly climatic fluctuations alter water supply availability. The decision to adopt a new or improved crop variety or cultivation practice is commonly made after referring to a locality's mean annual rainfall statistics. The problems caused by rainfall variability are compounded by high rates of evaporation and transpiration which can cause a soil to dry out very soon after rainfall, especially where soils are free-draining. Some tropical coastal vegetation and highland forests survive largely on intercepted mist and cloud, in some cases they may even exceed their interception capacity and contribute to stream flow and groundwater recharge. Usually polluted water supplies are more of a problem in the mid and lower portions of watershed/river basin ecosystems, where streams, groundwater lakes and reservoirs have become contaminated as a result of human industrial and agricultural activities.
