The influence of the diurnal variation of stability on potential evaporation Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ns064820w

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  • A method of calculating surface evapotranspiration by separately including the effects of vegetation and atmospheric evaporative demand under the condition of nonlimiting soil moisture is presented. A literature survey is conducted to determine the effects of plants on evapotranspiration. To represent the atmospheric evaporative demand, the original potential evaporation equation of Penman (1948) is utilized and then modified to include the effect of atmospheric stability using turbulent exchange coefficients formulated by Louis et al. (1982). The original and modified Penman expressions are compared for different asymptotic cases. Using boundary layer data from the Wangara experiment (Clarke et al., 1971), the diurnal variations of the original and modified Penman equations are compared. The daily total potential evaporation using linearized and integrated forms of the original and modified expressions are also compared. Finally, the nonlinear effects of averaging both the original and modified expressions are examined. It is found that including the diurnal variations of stability in the modified expression causes large hourly differences with the original expression under non-neutral conditions, while daily averages of the two compared fairly well. The diurnal variation of the surface moisture flux appears to be much larger than predicted by the original Penman expression. However, the original Penman expression remains a reasonable estimate of the 24-hour total potential evaporation.
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