Variability of surface soil moisture at the watershed scale

Data from the Washita '92 experiment illustrate the spatial and temporal variability of surface soil moisture. Statistical moments revealed that there is no significant skewness or kurtosis in the distribution. Over the drying period the variance decreased with time; however, the coefficient of variation did not significantly change, indicating that scaled variability remains roughly constant. Regression analysis showed that soil texture, vegetation density, and time since precipitation accounted for approximately 55% of the variability of surface soil moisture. There are also strong indications of persistence in the spatial structure representing perhaps topography and solar exposure, which was maintained and explained 31% of the total variability. The methodology proposed herein should be generally applicable in the analysis of any spatially variable land surface data set as it evolves with time.