Evapotranspiration

We review the measurements of latent and sensible heat flux made at seven flux tower sites during the Large-Scale Biosphere-Atmosphere Experiment for tropical humid, transitional and semideciduous forests, floodplain (with cerrado), and cerrado ecosystems. Measurements over farmlands in Amazonia vary from 1.2 (for bare soil) to 3 mm d^-1, with a reduction in the dry season. Estimates of evapotranspiration for Amazonia based on atmospheric reanalysis are generally higher than the measurements. Remarkably, for all the seven sites, the mean annual sensible heat flux ranged from 20 to 38 W m^-2, lower during the wet season and higher in the late dry season, consistent with the variation of net radiation and soil moisture. Based on the seasonal evapotranspiration, the sites are divided into two functional groups: tropical forest and savanna. At the northern sites (Manaus, Santarém), precipitation is above 1900 mm a^-1, monthly evapotranspiration is fairly constant during the wet season, ranges from 2.8 to 3.6 mm d^-1, progressively increases along the dry season up to 4 mm d^-1, and is dominated by net radiation and vapor density deficit. The western semideciduous forest in Rondônia presents similarities with the forest group, with monthly evapotranspiration that varies little but concurrent with net radiation year round, and peaks more exactly in the dryto- wet season transition. At the southern and eastern sites, precipitation is below 1700 mm a^-1, seasonal evapotranspiration is limited by soil moisture, ranges from 3 to 4 mm d^-1 in the wet season, and decreases in the dry season to 2.5 mm d^-1 in the transitional forest (Mato Grosso) and floodplain (Tocantins), and to 1 mm d^-1 in the São Paulo cerrado.