Spatiotemporal Variations in Soil Water: First Results from the ARM SGP CART Network

Abstract

A network of automated soil water and temperature systems, installed at 21 locations in Oklahoma and Kansas in 1996 and 1997, is providing hourly profiles of soil temperature and water at eight depths, from 0.05 to 1.75 m below the surface, in twin profiles 1 m apart. Dubbed the Soil Water and Temperature System (SWATS), these systems are an addition to the extended facilities of the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site. Average spacing between SWATS systems is about 75 km. The SWATS network is one of three overlapping soil water networks in the region but is unique in depth of deployment, providing observations of available soil water through most of the rooting zone of SGP pastures and prairies. A description of the SWATS sensor and network, calibration and data verification, and example time series from the first 3 yr of operation are presented. Perusal of the time series reveals systematic spatial and seasonal variations in soil water profile characteristics. These spatiotemporal variations are interpreted as the integrated response in varying soils to antecedent soil water and recent precipitation, under varying mixes of vegetation determined by climatic gradients in precipitation, with impacts from local pasture management.