Factors Controlling the Soil Moisture Spatial-Temporal Variability in the Shale Hills Watershed: A Hydropedologic Perspective.

It has been suggested that the spatial distribution and temporal variability of volumetric soil moisture (VWC) reflect underlying hydrologic processes operating at the watershed scale. An improved understanding of how hydrologic processes affect the spatial and temporal variability of VWC will allow for better land management practices and ultimately less degradation to riparian zones and lead to improved calibration and uncertainty reduction in large-scale climate models through better model representation of the spatial-temporal variability of soil moisture. To examine the spatio-temporal distribution of soil water within the Shale Hills watershed, we utilized high resolution digital elevation maps (DEM), soil physical properties data, and VWC data collected at multiple depths at 55 monitoring locations over a four year period. We examined the statistical properties of the soil moisture dataset to assess the relationship between soil moisture variability and mean watershed-wide soil moisture. We also examined the spatial correlation between VWC collected at different depths and soil-terrain spatial attributes. To assess the affect of soil and landscape position of soil moisture variability, we divided the monitoring locations into 4 distinct landform-soil groups identified from the DEM and during a site-specific soil surveys: Valley-Earnest soil, Swale Bottom-Rushtown soil, Swale Sideslope-Berks soil, and Hillslope/Summit-Weikert soil. Our results indicate that soil moisture spatial and vertical variability increases with an increase in mean watershed-wide VWC. Individually, we found that depth to bedrock had the highest correlation with VWC for all measurement days, and that terrain attributes were better predictors of spatial soil moisture values compared to soil attributes. The valley-earnest soils exhibited the largest spatial and vertical variability, while the hillslope-Weikert soil-landform group exhibited the lowest spatial and vertical variability. Lastly, our results suggest that soil moisture at depth significantly influences vertical variability of soil moisture. These results will aid in our understanding of the relationship between terrain-soil attributes and soil moisture as well as the factors controlling soil moisture variability through space and time.