Analysis and mapping of field-scale soil moisture variability using high-resolution, ground-based data during the Southern Great Plains 1997 (SGP97) Hydrology Experiment

Soil moisture is an important state variable in the hydrologic cycle, and i ts spatiotemporal distribution depends on many geophysical processes operat ing at different spatial and temporal scales. To achieve a better accountin g of the water and energy budgets at the land-atmosphere boundary, it is ne cessary to better understand the spatiotemporal variability of soil moistur e under different hydrologic and climatic conditions and at different hiera rchical 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 fi eld (Little Washita field site 07). The soil moisture measurements were mad e using portable impedance probes. Spatiotemporal data analyses of the two sampling events showed a significant change in the field variance but a con stant field mean, suggesting moisture was redistributed by (differential) b ase flow, evapotranspiration, and condensation. Among the different relativ e landscape positions (hilltop, slope, valley) the slope was the largest co ntributor 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 ev ents, indicating time instability in the spatial soil moisture data. Furthe rmore, high-resolution (impedance probe) sampling and limited (gravimetric) sampling gave different field means and variances.