Electrical resistivity and TDR methods for soil moisture estimation in Central Italy test-sites

In this study, the feasibility of the resistivity method for the study of the spatial and temporal soil moisture variations in the Vallaccia catchment (central Italy), covering an area of about 56km 2, was investigated. Correlation and regression analyses were performed over a 1year data set of simultaneous soil electrical resistivity and soil moisture measurements, acquired in eight different sites with a Resistivimeter Syscal Junior and a portable Time Domain Reflectometer (TDR), respectively. Measurements acquired in-time by continuous Frequency Domain Reflectometer (FDR) sensors were also used and compared with simultaneous resistivity measurements. The statistical analyses were conducted not only for the whole data set, but also separately for each sampling day, for each sampling site and considering spatially averaged data. Results showed a good correlation between resistivity and soil moisture measurements, revealing the capability of resistivity measurements to infer soil moisture spatial and temporal variability with a root mean square error equal, on average, to 4.4% vol/vol. In comparison with TDR, the resistivity method gives information integrated on a greater volume of soil and the measurements are easier and quicker to be carried out. Therefore, this method can be considered as an alternative tool to be employed for qualitative and quantitative soil moisture monitoring in small to medium catchments.