Reconciliation between Measured and Theoretical Temperature Effects on Soil Water Retention Curves

Because temperature has a considerable effect on water retention curves, it should be accounted for when modeling unsaturated soil water flow under nonisothermal conditions. Changes are commonly attributed to alterations in surface tension at the air‐water interface, to changes in the volume of entrapped air, and sometimes to the presence of contaminants at the air‐water interface. Predicted changes have, however, always fallen short of experimentally determined values reported in the literature. We propose a new theory that considers soil water to be composed of continuous water and isolated packets of water. Measured soil water pressure head values are assumed to be determined by the properties of continuous water only. We hypothesize that, when the temperature increases, water flows from isolated packets to the continuous water phase, thus resulting in an additional temperature effect on the water retention curve. Based on the assumption that the continuous water content changes linearly with the total water content, we derived expressions for the change in soil water pressure head with temperature. Calculated changes in points on the water retention curve were subsequently much closer to measured values than previously reported. The good agreement between measured and predicted results suggests that more definitive experiments be conducted to investigate the role of isolated water packets on soil water retention curves.