Evaporation from Amazonian rainforest

The results of a two-year Anglo-Brazilian study of the micrometeorology and process hydrology of undisturbed tropical rainforest at a site in central Amazonia are described. Sample measurements of dry-canopy evaporation from three intensive field campaigns and continuous measurements of rainfall interception loss are used to calibrate a micrometeorological model of evaporation from the forest canopy. Evaporation at this site is calculated by the model from September 1983 to September 1985 by using hourly-average meteorological measurements routinely taken above the canopy, and regular measurements of soil water tension averaged to a depth of one metre. The monthly evaporation derived in this way is compared with the measured precipitation and radiant energy input to the forest, and with calculated potential evaporation rates. Over the whole study period, approximately 10% of rainfall was intercepted by the forest canopy, and this accounted for 20-25 % of the evaporation. The remainder occurred as transpiration from the trees. Over this same period, about one half of the incoming precipitation is returned to the atmosphere as evaporation, a process which requires 90% of the radiant energy input. These proportions exhibit some seasonal behaviour in response to the large seasonal variation in rainfall. The average evaporation over two years was within 5% of potential evaporation. Monthly-average evaporation exceeds potential estimates by about 10% during wet months, and falls below such estimates by at least this proportion in dry months. These data provide the hitherto missing numerical basis for assessing the likely consequences of Amazonian deforestation on surface water and energy balances.

[1]  C. R. Lloyd,et al.  The measurement and modelling of rainfall interception by Amazonian rain forest , 1988 .

[2]  C. J. Moore,et al.  Estimating heat storage in Amazonian tropical forest , 1986 .

[3]  J. Gash,et al.  A note on estimating the effect of a limited fetch on micrometeorological evaporation measurements , 1986 .

[4]  C. R. Lloyd,et al.  A microprocessor system for Eddy-correlation , 1984 .

[5]  W. J. Shuttleworth,et al.  Observations of radiation exchange above and below Amazonian forest , 1984 .

[6]  W. James Shuttleworth,et al.  Eddy correlation measurements of energy partition for Amazonian forest , 1984 .

[7]  C. J. Moore.  On the calibration and temperature behaviour of single-beam infrared hygrometers , 1983 .

[8]  C. J. Moore,et al.  A switched continuous-wave sonic anemometer for measuring surface heat fluxes , 1982 .

[9]  J. R. Garratt,et al.  Surface influence upon vertical profiles in the atmospheric near-surface layer , 1980 .

[10]  C. R. Lloyd,et al.  Comparative estimates of interception loss from three coniferous forests in Great Britain , 1980 .

[11]  M. Raupach.  Anomalies in flux-gradient relationships over forest , 1979 .

[12]  W. James Shuttleworth,et al.  Has the Priestley-Taylor Equation Any Relevance to Forest Evaporation? , 1979 .

[13]  J. Gash,et al.  An application of the Rutter model to the estimation of the interception loss from Thetford Forest , 1978 .

[14]  W. J. Shuttleworth,et al.  A simplified one-dimensional theoretical description of the vegetation-atmosphere interaction , 1978 .

[15]  J. Gash,et al.  The evaporation from Thetford Forest during 1975 , 1977 .

[16]  Jack Kornfield,et al.  A Comparative Study of the Effects of Albedo Change on Drought in Semi-Arid Regions. , 1977 .

[17]  I. Calder.  A model of transpiration and interception loss from a spruce forest in Plynlimon, central Wales , 1977 .

[18]  W. J. Shuttleworth,et al.  A one-dimensional theoretical description of the vegetation-atmosphere interaction , 1976 .

[19]  P. Jarvis.  The Interpretation of the Variations in Leaf Water Potential and Stomatal Conductance Found in Canopies in the Field , 1976 .

[20]  A. Rutter,et al.  A Predictive Model of Rainfall Interception in Forests. II. Generalization of the Model and Comparison with Observations in Some Coniferous and Hardwood Stands , 1975 .

[21]  A. Dyer.  A review of flux-profile relationships , 1974 .

[22]  C. Priestley,et al.  On the Assessment of Surface Heat Flux and Evaporation Using Large-Scale Parameters , 1972 .

[23]  A. C. Chamberlain,et al.  Transport of gases to and from grass and grass-like surfaces , 1966, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[24]  H. L. Penman.  Natural evaporation from open water, bare soil and grass , 1948, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[25]  C. Lloyd,et al.  Spatial variability of throughfall and stemflow measurements in Amazonian rainforest , 1988 .

[26]  R. Clarke.  The interception process in tropical rain forests: a literature review and critique (*). , 1986 .

[27]  E. Matsui,et al.  HYDROLOGICAL ASPECTS OF THE TROPICAL RAIN-FOREST IN CENTRAL AMAZON , 1984 .

[28]  J. Gash,et al.  SIM5T/12 - a Model of Forest Transpiration and Interception, Using Data from an Automatic Weather Station , 1979 .

[29]  J. Garratt.  Flux profile relations above tall vegetation , 1978 .

[30]  J. Gash,et al.  Comparison of aerodynamic and energy budget estimates of fluxes over a pine forest , 1975 .

[31]  A. S. Thom,et al.  Energy budgets in pine forest , 1973 .

[32]  A. S. Thom,et al.  Momentum, mass and heat exchange of vegetation , 1972 .

[33]  A. Rutter,et al.  A predictive model of rainfall interception in forests, 1. Derivation of the model from observations in a plantation of Corsican pine , 1971 .