Soil moisture temporal stability over experimental areas in Central Italy

The knowledge of the near-surface soil moisture spatio-temporal pattern is an important issue for hydrological and climatic studies. Because of its high spatial and temporal variability, soil moisture monitoring scheme was investigated in view of its application in rainfall–runoff modelling. To this end, through a portable Time Domain Reflectometer, 35 measurement campaigns were carried out at three experimental areas ranging in extension from nearly 400 to 9000 m2 and located in central Italy. Based on the results of the temporal stability analysis, for each experimental site the location able to accurately represent the field-mean soil moisture was detected in terms of root mean square error, less than 2%. Moreover, the location was also found to be linked to topographical characteristics, primarily the upslope drainage area but also the slope and the elevation. This aspect allowed both to identify these locations also in ungauged areas and to better understand processes affecting the soil moisture spatial pattern. By matching the temporal pattern observed at the different experimental sites, factors affecting the soil moisture spatio-temporal behavior were analyzed. Results showed that the soil moisture monitored in a few locations, better if previously identified as "representative", provides useful information not only at the plot scale (∼ 10,000 m2) but also over large areas that are of up most importance for hydrological applications.