Real evapotranspiration and transpiration through a tropical rain forest in central Amazonia as estimated by the water balance method

The research was carried out from January 1981 to December 1983, in a small watershed of 1.3 km 2 surface area located at INPA's Ducke Forest Reserve. This watershed is drained by the Barro-Branco stream, and its vegetation cover is characterized by a typical tropical rain forest of the central Amazon region. In order to estimate its real evapotranspiration, transpiration and other hydrological parameters, the precipitation and the discharge yielded by the Barro-Branco stream were measured during the experimental period. A mean precipitation of 2209 mm year −1 was recorded, from which 67.6% was lost to the atmosphere through evapotranspiration. This result was similar to that calculated by the modified Penman's method (1479.2 mm year −1). If the average rain water interception by the forest canopy is assumed to be 11.3% of the total precipitation amount, as estimated by Gash's model, the transpiration was 1243.7 mm year −1, representing 56.3% of the total rainfall observed for the 1981–1983 period.