Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/1999
Publication Date: N/A
Interpretive Summary: The amount of moisture present in soil affects agriculture and engineering, and influences environmental phenomena such as flooding and climate. A better understanding of soil moisture and its distribution in space and time would permit greater control over these important activities and phenomena. Soil moisture content changes as you move across a landscape. The variability arises from a complex interaction of many geophysical parameters such as soil type, topography, vegetation, and climate. A complicating factor is that the relationship between soil moisture and the other parameters changes depending on the space and time scales that you consider. This study was done to improve our understanding of soil moisture and its relationship to landscape position and topography. A statistical analysis of soil moisture data showed that landscape slope position was the most important factor contributing to the variability of soil moisture in a 16 acre field over 24 hours. This work will benefit scientists who are trying to better understand soil moisture and its distribution in space and time.
Technical Abstract: 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 probes) sampling and limited (gravimetric) sampling gave different field means and variances.