Heat and Water Movement Under Surface Rocks in a Field Soil: I. Thermal Effects

Abstract

AbstractResults of a field experiment designed to evaluate the effect of surface rocks on soil heat flow are presented. Temperature observations were made by thermocouples at 12 locations under and adjacent to rocks placed over bare soil. Continuous readings were taken for 24‐ and 48‐hour intervals using seven different kinds of rock cover, ranging from large granite slabs to gravel piles, during the time between December 1974 and August 1975.Experimental results consistently showed a nonnegligible 24‐hour net horizontal heat flow toward the rock at both the 2.5 and 5.0 cm depth. Net vertical heat flow was always downward in the soil under the bare surface, but was observed to be either upward or downward in the soil under the rock cover depending on prior conditions. Because water vapor movement in moist soil is generally in the same direction as heat flow it was suggested that surface rock cover may be a mechanism for water collection in arid climates.A simulation model was constructed to describe two‐dimensional heat flow in a uniform soil with a rectangular rock on the surface. Using the measured surface temperature as boundary values and a soil thermal conductivity corresponding to the mean daily soil surface temperature, the simulation model adequately reproduced the observed temperatures under and adjacent to the rock.