This study uti lized a 4-yr database consisti ng of catchment-wide volumetric soil moisture measurements at 78 locati ons from the surface down to 1.1 m depth within the 7.9-ha Shale Hills Criti cal Zone Observatory in central Pennsylvania. The objecti ves were to: (i) assess the uncertainty in esti mati ng catchment-wide mean soil moisture content by characterizing the relati onship between soil moisture spati al variability and spati ally averaged moisture content and (ii) examine the relati onship between temporal changes in soil moisture spati al variability and seasonal and event-based hydrologic fl uxes. Our results showed that soil moisture spati al variability increased exponenti ally with increasing catchment-wide wetness across all measurement depths and various soil-landform units. This relati onship led to the widening of confi dence intervals and an increase in the number of sites needed to obtain 95% confi dence in spati ally averaged soil moisture as the catchment wets up. This was due to the well-drained and steep-sloped hillslope soils in the catchment that confi ned saturated areas to the swales and the valley fl oor. Temporal changes in soil moisture spati al variability indicated a seasonal increase in the catchment-wide soil moisture variability that coincided with the emergence of a shallow water table in the valley during the winter and spring months. Event-based increases in soil moisture spati al variability associated with large antecedent precipitati on were also observed (but with limited resoluti on because of weekly to biweekly measurements), which indicated the importance of subsurface lateral fl ow in infl uencing the catchment-wide soil moisture spati al variability. Because ephemeral shallow water tables and subsurface lateral fl ow are common in many temperate forests, our results are useful for guiding soil moisture monitoring campaigns in these catchments and have implicati ons for interpreti ng and scaling remote sensing footprints of soil moisture in these landscapes during diff erent ti mes of a year. Abbreviati ons: AI3, 3-d antecedent precipitati on index; CHS, concave hillslope; PHS, planar hillslope and ridgetop; SLU, soil-landform units; TDR, ti me domain refl ectometry; VLY, valley fl oor.Spati al and temporal variability of soil moisture infl uences environmental and ecological processes from the pedon to the global scales. At the regional scale, the spatial distribution of soil moisture provides an important feedback mechanism for climate dynamics and is an important control on the division of solar energy into latent and sensible heat (Koster et al., 2003;D'Odorico and Porporato, 2004). At the catchment scale, the distribution of soil moisture in space and time infl uences the nonlinear behavior of a catchment's response to storm events and the partitioning of precipitation into stream runoff , infi ltration, and storage within the soil zone (Meyles et al., 2003;Zehe and Bloschl, 2004;James and Roulet, 2009). Our ability to model these hydrological processes requir...

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