Field procedure for estimating soil thermal environments.
1987
Flint A.L. | Childs S.W.
Intensive measurements are required to precisely define soil temperature, heat flux, and thermal properties of heterogeneous forest soils. Fifty detailed profiles of temperature, density, and water content were used with the conduction heat flow equation to estimate soil thermal properties for a clearcut harvest area in a mixed conifer forest in southwest Oregon. These profiles were used to determine the accuracy with which soil temperatures could be modeled and the number of soil layers required to characterize a given field site. The soil was modeled as a profile of between 1 and 21 layers of known (measured) volumetric heat capacity and measured initial and boundary conditions. Soil thermal conductivity for each layer was determined for each of 50 datasets using an iterative numerical procedure. The accuracy of the various models was assessed by comparing the error between measured and modeled profiles. For the skeletal soil studied, a numerical model and field measurements of four soil layers proved to be the best combination of accuracy and simplicity. The assumption of a homogenous (1-layer) profile was satisfactory in several cases. The need for detailed field measurements was assessed by comparing modeled and measured soil temperature: minimum and maximum temperature, duration of high temperature and low temperature events, and positive and negative heat flux. Models based on measurements from four or more soil layers predicted soil temperature within +/- 0.3 degrees C of measured values. Models based on two or more measured soil layers were within +/- 0.006 MJ m-2 of measured daily positive heat flux.
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