The vertical and horizontal distribution of soil moisture is becoming increasingly important to both land managers and scientists in the fields of hydrology, soil science and ecology, amongst others. As geophysical tools are being developed to remotely estimate spatial patterns of soil moisture, we remain dependent on in situ measurements, which are costly in time and research dollars, especially in hilly terrain with high spatial variability. Methods for predicting the spatial patterns of soil moisture and areas of highly correlated behavior are needed to reduce the number of monitored sites and the spatial extent of surveying in the field. While topographic indices have shown some promise as tools in predicting the spatial patterns of soil moisture, they rarely predict more than 50% of the observed variance. Further work is clearly needed to predict soil moisture at the finer spatial and temporal resolutions with higher accuracy. We present an ongoing analysis of the spatial and temporal dynamics of soil moisture at the Shale Hills Critical Zone Observatory in central Pennsylvania. Over 4 years of weekly soil moisture measurements at over 100 sites in 10 cm vertical increments in this small (8 ha) catchment have allowed for an improved understanding of the patterns of soil moisture at the catchment scale, both spatially and temporally. While, as at other similar sites, the spatial pattern of soil moisture is insufficiently predicted by topographic indices, the majority of the sites are well correlated with each other. We will explore which sites are acting in concert (sites dominated by non local controls such as upslope contributing area, aspect, etc.), and which sites are poorly predicted by their neighbors (dominated by local controls such as soil depth, texture, and horizonation). These analyses are performed on measurements taken at various depths to the soil-bedrock interface, allowing for analysis in both lateral and vertical directions. We will use these analyses to develop a framework for predicting soil moisture throughout the catchment based on limited spatial measurements, and to identify critical locations necessary for installation and monitoring of soil moisture. This framework will have implications for both the extrapolation of limited measurements at other field sites, as well as the design of field monitoring system.
Graham, C.B., Lin, H. (2009): A framework for predicting spatial patterns of soil moisture dynamics at the catchment scale. AGU Annual Fall Conference Proceedings.
This Paper/Book acknowledges NSF CZO grant support.