Energy and water dynamics of a central Amazonian rain forest

Abstract

This paper presents measurements of the energy and water budgets of a tropical rain forest near Manaus, Brazil, in central Amazonia, collected between September 1995 and August 1996. Fluxes of sensible and latent heat were measured using a three‐dimensional eddy covariance system mounted above the forest canopy. Using a new approach to analysis of eddy covariance data, we found that the measured fluxes increased significantly when turbulent transport on timescales of 1 to 4 hours was taken into account. With this new analysis, the measured turbulent fluxes almost balanced the incoming net radiation, giving increased confidence in the accuracy of the measured fluxes. Of the 5.56 GJ m−2 yr−1 of solar radiation supplied over the year, 11% were reflected, 15% were lost as net thermal emission, 27% were transported through sensible heat convection, 46% used in evapotranspiration, and 0.5% were used in net carbon fixation. Total annual evapotranspiration was calculated to be 1123 mm, accounting for 54% of total precipitation. Seasonality was an important influence: limited water availability during the dry season caused evapotranspiration to reduce by 50%. Total canopy conductance was linearly correlated to soil moisture content, with typical midday values ranging between 0.8 mol m−2 s−1 in the wet season and 0.3 mol m−2 s−1 in the dry season. Such seasonal behavior is likely to be prevalent in most tropical forest regions, and correct description of dry‐season evapotranspiration will require accurate modeling of plant and soil hydraulic properties and knowledge of root distributions.