Aspects of soil moisture variability in the Washita '92 study region

The Washita '92 experiment, which took place in the Little Washita River watershed in Oklahoma, generated maps describing the volumetric surface soil moisture field during an 8-day drying period. The Little Washita is part of the Red River basin, a major tributary of the Lower Mississippi, A semivariogram analysis revealed that the surface soil moisture field of this 18 km x 25 km study region as a whole was spatially nonstationary and exhibited certain fractal characteristics. However, for smaller subareas within the study region,it was determined that the moisture field could be considered stationary for distances smaller than 5 km, with ranges of approximately 1 km over which surface soil moisture was spatially correlated. A semivariogram analysis for each of the individual soil types over the entire Washita '92 region revealed that surface soil moisture was stationary within each soil type, again with a range of correlation of approximately 1 km, This indicates that soil moisture variability is strongly affected by soil type.