The water budget of an amazonian rain forest

Abstract In a tropical rain forest near San Carlos de Rio Negro, Venezuela, average yearly precipitation from September 1, 1975, through August 31, 1977 was 3664 mm. Throughfall was 87% of precipitation, stem flow was 8%, transpiration was 47%, evaporation from leaf surfaces was 5%, and sub-surface runoff was 48%. These results conform closely to the prediction of Marques et al. (1977) that 48% of the precipitation that falls on the central Amazon Basin is derived from evapotranspiration within the Basin. Resumo Foram feitas medições de economia do água numa floresta tropical úmida perto de San Carlos de Rio Negro (Venezuela), no período de 1 9.1975 a 31.8.1977, as quais causaram: Precipitação média anual — 3.664mm: água de lavagem das folhas — 87% de precipitação: água de escorrimento dos troncos — 8%: transpiração — 47%; evaporação das folhas — 5%; e o fluxo sub-superficial — 48%. Esses dados concordam com os de Marques et al. (1977) que afirmaram que 48% da precipitação na Amazônia Central é derivada da exapotranspiração dentro da bacia.