45 Actual Evaporation
Part 4. Hydrometeorology
Published Online: 15 APR 2006
Copyright © 2005 John Wiley & Sons, Ltd
Encyclopedia of Hydrological Sciences
How to Cite
Dolman, A. J. 2006. Actual Evaporation. Encyclopedia of Hydrological Sciences. 4:45.
- Published Online: 15 APR 2006
Actual evaporation concerns the evaporation from natural surfaces. Globally actual evaporation from the land amounts to around 71 103 km3 year−1. Measurement of evaporation occurs by water balance techniques or directly through micrometeorological techniques. Actual evaporation depends on land cover and meteorological conditions. Evaporation can be predicted by various equations, amongst the Penman-Monteith equation which takes into account both the vegetation properties as well as the meteorological conditions. In the case of sparsely vegetated areas soil evaporation and plant evaporation need to be treated separately. Estimating the correct value of surface conductance is a critical issue in applying the Penman-Monteith equation, but models exists. Evaporation from bare soil can be treated as a two stage process, with rapid evaporation at potential rates after rain, and subsequent drying. At larger than catchment scales, feedbacks with the atmospheric boundary layer make it possible to apply evaporation equations based on equilibrium concepts, such as the Priestley-Taylor equation. There has been substantial progress in evaporation modeling and measurements over the last 25 years. This knowledge can be used much more in assessing changes in evaporation of catchments that may result from perturbations in land use and climate.
- actual evaporation;
- surface resistance;
- aerodynamic resistance;
- soil evaporation;
- sparse crop evaporation;
- equilibrium evaporation