Department of Earth System Science

Soil moisture is an important state variable in the hydrologic cycle, and its spatiotemporal distribution depends on many geophysical processes operating at different spatial and temporal scales. To achieve a better accounting of the water and energy budgets at the land-atmosphere boundary, it is necessary to better understand the spatiotemporal variability of soil moisture under different hydrologic and climatic conditions and at different hierarchical space scales and timescales. During the Southern Great Plains 1997 (SGP97) Hydrology Experiment the 0–6 cm soil water content was measured on consecutive afternoons at 400 locations in a small, gently sloping range field (Little Washita field site 07). The soil moisture measurements were made using portable impedance probes. Spatiotemporal data analyses of the two sampling events showed a significant change in the field variance but a constant field mean, suggesting moisture was redistributed by (differential) base flow, evapotranspiration, and condensation. Among the different relative landscape positions (hilltop, slope, valley) the slope was the largest contributor to the temporal variability of the soil moisture content. Using a sequential aggregation scheme, it was observed that the relative position influencing the field mean and variance changed between the two sampling events, indicating time instability in the spatial soil moisture data. Furthermore, high-resolution (impedance probe) sampling and limited (gravimetric) sampling gave different field means and variances.