Soil moisture variability across climate zones

Variability in soil moisture is controlled by temporal variability in atmospheric conditions and spatial variability in land-surface conditions. Observations of soil moisture have revealed a variety of patterns - generally, in semiarid regions variance increased as mean soil moisture content increased, in humid regions variance decreased as mean soil moisture content increased, and in temperate regions variance peaked at intermediate moisture contents. We collected soil moisture data at Big Meadows, an upland wetland in Shenandoah National Park, Virginia, and we observed peak variance at intermediate moisture contents, consistent with other sites in temperate climate zones. A modified soil moisture dynamics model was used to examine how soil moisture patterns evolve through time, how topography, soil, and vegetation affect these patterns, and how the trends observed across climate zones can be explained. The trends observed relate to theoretical bounds on soil moisture distributions, i.e., the wilting point and the porosity.