EOF analysis of surface soil moisture field variability

This study investigated the characteristics of spatial and temporal variability of soil moisture field by means of the empirical orthogonal functions (EOFs). The relative roles of various affecting factors (topography, soil properties, vegetation, etc.) to the spatial variability of soil moisture contents have also been evaluated. Two soil moisture data, the SGP97 Little Washita field site 10 and 13 gravimetric soil moisture data (the LW10 and LW13), were used for this study. Summarizing the results is as follows. First of all, the results obtained fully support the previous findings, especially the importance of topography-related factors. Additionally, this study has revealed the importance of role changes of several affecting factors, especially the topography- and the soil-related ones. The effect of rainfall was also found very significant for the time evolution of soil moisture field variability. Even though the two data fields used in this study are located within the range of hydrological and meteorological homogeneity, the underlying mechanism of controlling the temporal and spatial variability of soil moisture field are found very different. In conclusion, there seems no simple and unique mechanism to be applied to explain the evolution of soil moisture field. Even though the topography-related factors are found to be most dominant to control the spatial organization of soil moisture contents, other factors like the soil and land use are also found significant for the entire period or for some time period after rainfall stops.