Graduate Thesis Or Dissertation
 

Measured and modeled energy balance parameters to evaluate the environmental conditions of reforestation

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  • In order to develop three models for use in quantifying the environmental conditions of reforestation, extensive measurements required for energy balance calculations were taken for a reforestation site in southwest Oregon. The models are used to decrease the number of measurements required to properly evaluate the potential for heat or moisture stress at a specific reforestation site. The first model, a modification of the Priestley-Taylor evaporation equation, is calibrated to allow prediction of actual evaporation from net radiation and soil heat flux under nonsaturated, soil water limited conditions. By combining Bowen ratio measurements of evaporation and soil water content, an equation was developed to calculate a modified Priestley-Taylor coefficient, α', as a function of soil water content. When the soil is near field capacity α' is ≈ 0.85. Under drier soil conditions, the decrease in α is well described by an exponential equation. The soil water content did not become limiting to evapotranspiration until 60 percent of the available water was used. The second model uses the inverse solution to the soil heat flow equation to determine soil thermal conductivity for layered, heterogeneous soils. The results of the model indicate that soil thermal properties could be adequately modeled by separating the soil into four physical layers to account for the variability in soil water content, bulk density and rock fragment content. The four layer soil model could predict temperatures within 0.3°C and soil heat flux within 0.006 MJ /m² /day. The third model predicts solar radiation. The model incorporates thorough treatment of all components of radiation, (Rayleigh scatter, aerosol scatter, multiple reflected, ground reflected and direct beam radiation) yet only requires the basic site measurements of slope, aspect, latitude, longitude, elevation, and ground albedo. These data are combined with a simple estimate of turbidity (either from a local weather station or literature values) and literature values for atmospheric content of ozone and water vapor to provide a good estimate of potential solar radiation. The model also considers the anisotropic distribution of diffuse radiation and the strong influence that blocking ridges have on total diffuse radiation as well as direct beam. The model was tested using data collected from six sites with different atmospheric conditions and topographic settings.
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