Access to resource reserves in deep soil during periods of drought determines whether or not the tropical moist forests of Amazonia will be buffered from the deleterious effects of water deficit. Severe water stress may lead to tree mortality, changes in forest composition, and greater susceptibility to fire. A model was developed to simulate changes in the distribution of soil water within an existing throughfall exclusion experiment located in the Tapajs National Forest, east-central Amazonia (Brazil). Simulations using 2.5 years of data capture mild soil water depletion near the surface after the first treatment year, and decreasing soil moisture at depth during the second treatment year. Sensitivity analysis revealed that the model is sensitive to the parameters of the water retention and unsaturated flow equations. The model may be used to determine whether and how throughfall exclusion from a tropical rain forest affects water and nutrient cycling.
