Most representations of the hydrologic cycle assume that nearly all precipitation over land surfaces reaches the ground, but depending on the nature of vegetation growing from the surface, significant amounts of moisture may be intercepted by plant surfaces. Previous research indicates that interception rates are highest in tropical rainforests, where tree canopies are most dense. As tropical forests are cleared, the amount of moisture falling directly onto the ground may therefore dramatically increase, further exacerbating the microclimatological changes that result from deforestation. No accurate measurements of the amounts of moisture intercepted by tree canopies have been made, however, so estimates of the volume of water flows from the atmosphere through vegetative surfaces to the ground remain conjectural. This project will test a new procedure to measure the amount of precipitation that passes through successive levels of tree canopies to the land surface. Such measurements are complicated by high winds that blow raindrops horizontally through the treetops. A geographic information system-based, three-dimensional model of air and moisture flow through cyclone-prone tropical rainforests will be developed and tested at a study site on the Atherton Tableland of Queensland in northeastern Australia. Wind sensors, tipping-bucket and tilted rain gauges, and instruments to measure the angle of inclined rainfall will be used to gather data for testing the model. This research project will provide an effective test of a new model and methods for measuring the amount of moisture intercepted by tree canopies. Although initially calibrated for tropical rainforests, the model and methods will be adaptable for other types of biomes. The data gathered using these methods and the refined model will permit testing of important hypotheses about the nature and volume of water movements among the atmosphere, vegetative surfaces, and the ground. It therefore will enhance our understandings of a critical part of the hydrologic cycle and will improve models of atmospheric-terrestrial interaction. Because new insights will be gained on the dynamics of tropical rainforests, this project also will increase our understanding of these critical areas of especially great environmental change.
