Evaluating a Model of Evaporation and Transpiration with Observations in a Partially Wet Douglas-Fir Forest

Authors: Bosveld F.C.1; Bouten W.2

Source: Boundary-Layer Meteorology, Volume 108, Number 3, September 2003 , pp. 365-396(32)

Publisher: Springer

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Abstract:

The Penman–Monteith equation is extended to describe evaporation of intercepted rain, transpiration and the interaction between these processes in a single explicit function. This single-layer model simulates the effects of heat exchange, stomatal blocking and changed humidity deficit close to the canopy as a function of canopy water storage. Evaporation depends on the distribution of water over the canopy and the energy exchange between wet and dry parts. Transpiration depends on the dry canopy surface resistance that is described with a Jarvis-type response. The explicit functions obtained for water vapour fluxes facilitate a straightforward identification of the various processes. Canopy water storage amounts and xylem sapflow were measured simultaneously during drying episodes after rainfall in a dense, partially wet, Douglas-fir forest. Estimates of evaporation and transpiration rates are derived from these observations. The analysis shows that evaporation induced transpiration reduction is mainly caused by energy consumption. Changes in water vapour deficit have a minor effect due to a compensating stomatal reaction. The remaining difference between observed and modelled transpiration reduction can be attributed to partial blocking of stomata by the water layer.

Keywords: Evaporation; Forest; Hydrology; Interaction; Penman–Monteith equation; Transpiration; Wet canopy

Language: English

Document Type: Research article

Affiliations: 1: Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE, De Bilt, The Netherlands 2: Institute of Biodiversity and Ecosystem Dynamics – Physical Geography, University of Amsterdam, The Netherlands

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