ARS | Publication request: Temporal stability of soil water contents: A review of data and analyses

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 2012
Publication Date: June 6, 2012
Citation: Vanderlilnden, K., Vereecken, H., Hardelauf, H., Herbst, M., Martinez, G., Cosh, M.H., Pachepsky, Y.A. 2012. Temporal stability of soil water contents: A review of data and analyses. Vadose Zone Journal. DOI:10.2136/vzj2011.0178.

Interpretive Summary: Surveys of various landscapes have shown that some locations have soil water contents consistently higher than the average across the entire area, while other locations have consistently lower average water contents. This phenomenon is termed “temporal stability of soil water contents”. Characterization of the temporal stability has found wide applications: in remote sensing of soil moisture, in precision farming, in optimizing resources for soil water content monitoring, in designing soil water sensor networks and in applications requiring both upscaling and downscaling soil water contents. With the exponential growth of research and applications of the temporal stability in soil water contents, there exists a need for a comprehensive review of data and methods in this field. This review is a synthesis of all of the data and methods available in the world literature. We have also proposed a new model of temporal stability which can be used to condense temporal stability data. We summarized information on controls of the temporal stability of soil water contents, outlined gaps in the knowledge and identified prospective research avenues. Results of this work will be useful to agronomist, hydrologists, meteorologists, and other providers and users of soil water content data in that they provide guidance and methods on data analysis and present references and descriptions of test cases for comparisons and data acquisition designs.

Technical Abstract: Temporal stability of soil water content (TS SWC) has been observed throughout a wide range of spatial and temporal scales. Yet, the evidence with respect to the controlling factors on TS SWC remains contradictory or non-existing. The objective of this work was to develop the first comprehensive review of methodologies to evaluate TS SWC and to present and analyze the inventory of published data. Statistical analysis of mean relative difference (MRD) data and associated standard deviations (SDRD) from 157 graphs in 37 publications, showed a trend for the standard deviation of MRD (SDMRD) to increase with scale. The MRD had generally the Gaussian distribution with R2 ranging from 0.841 to 0.998. No relationship between SDMRD and R2 was observed. The smallest R2 values were mostly found for negatively skewed and platykurtic MRD distributions. A new statistical model for temporally stable SWC fields was proposed. The analysis of the published data on seven measurement-, terrain-, and climate-related potentially controlling factors of TS SWC suggested intertwined effects of controlling factors rather than single dominant factors. This calls for a focused research effort on the interactions and effects of measurement design, topography, soil, vegetation and climate on TS SWC. Research avenues are proposed which will lead to a better understanding of the TS phenomenon and ultimately to the identification of the underlying mechanisms.