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Evaporation of intercepted rainfall from isolated evergreen oak trees: Do the crowns behave as wet bulbs?
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Advisor(s)
Abstract(s)
A new approach is suggested for estimating evaporation of intercepted rainfall from single
trees in sparse forests. It is shown that, theoretically, the surface temperature of a wet tree
crown will depend on the available energy and windspeed. But for a fully saturated canopy
under rainy conditions, surface temperature will approach the wet bulb temperature when
available energy tends to zero. This was confirmed experimentally from measurements of
the radiation balance, aerodynamic conductance for water vapour and surface temperature
on an isolated tree crown. Net radiation over a virtual cylindrical surface, enclosing the tree
crown, was monitored by a set of radiometers positioned around that surface. Aerodynamic
conductance for the tree crown was derived by scaling up measurements of leaf boundary
layer conductance using the heated leaf replica method. Thermocouples were used to
measure the average leaf surface temperature. Results showed that a fully wet single tree
crown behaves like a wet bulb, allowing evaporation of intercepted rainfall to be estimated
by a simple diffusion equation for water vapour, which is not restricted by the assumptions
of one-dimensional transfer models usually used at the stand scale. Using this approach,
mean evaporation rate from wet, saturated tree crowns was 0.27 or 0.30mm h 1, when
surface temperature was taken equal to the air wet bulb temperature or estimated accounting
for the available energy, respectively.
Description
Keywords
Evaporation Rainfall interception Isolated trees Quercus ilex Wet bulb temperature Surface temperature
Citation
PEREIRA, F.L. [et al.] (2009) - Evaporation of intercepted rainfall from isolated evergreen oak trees: Do the crowns behave as wet bulbs? Agricultural and Forest Meteorology. 149:3-4, p. 667-679. DOI: 10.1016/j.agrformet.2008.10.013