Abstract
Understanding the spatio-temporal dynamic of soil moisture is critical in hydrological and other land surface related studies. Until recently, however, there have been controversies about the relationship between spatial mean and spatial variance of soil moisture and the contributions of each of these factors to spatial variability. Therefore, in this study, spatial variability of soil moisture in a 7 km2 forest catchment is analyzed by time-series data on soil moisture obtained at a total of 12 observation sites. Results showed that soil moisture spatial mean and spatial variance varied almost synchronously and in three cyclic patterns during the monitoring period from 1 April 2015 to 31 October 2015. The spatial mean-variance relationship during the ascending and descending periods of spatial mean could be well-fitted by upward and downward convex quadratic curves, respectively, indicating possible clockwise hysteresis of this relationship. It was found that all through the monitoring period, contributions of time-invariant factors on total spatial variance increased from 68.9% to 88.2% with depth, and temporally stable ranking of sites was obtained. Because of the high spatial variation of soil moisture in our study area, it should be noted that a large number of sample plots would be needed to adequately estimate the spatial variability of soil moisture.
Highlights
While soil moisture is quantitatively negligible in the global water budget [1], seldom would anyone doubt its importance in studies concerning hydrological and other land surface processes.Soil water is a necessity for growth of vegetation and other soil-born living beings, and one of the major controlling factors in partitioning of surface runoff and infiltration, as well as in partitioning of latent and sensible heat at ground surface [2]
The dataset was obtained by monitoring soil moisture at a total of I sites with J depths K times, and θijk represents soil moisture at the jth (j “ 1, . . . , J) depth of the ith (i “ 1, . . . , I) site measured at the kth (k “ 1, . . . , K) time point
We examined the ranks of sites in each of the three periods, and a Spearman test showed that ranks of sites through the whole monitoring period were significantly correlated
Summary
While soil moisture is quantitatively negligible in the global water budget [1], seldom would anyone doubt its importance in studies concerning hydrological and other land surface processes.Soil water is a necessity for growth of vegetation and other soil-born living beings, and one of the major controlling factors in partitioning of surface runoff and infiltration, as well as in partitioning of latent and sensible heat at ground surface [2]. While soil moisture is quantitatively negligible in the global water budget [1], seldom would anyone doubt its importance in studies concerning hydrological and other land surface processes. In hydrological studies, grid mean or representative soil moisture content is normally required, for example, to initiate and validate forecasting models [4,5] and to estimate regional water storage [6]. Soil moisture obtained through ground-based measuring campaigns is basically limited to point scales, resulting in scale mismatch between observations and applications of soil moisture. This problem and the work of upscaling have challenged researchers for a long time, Forests 2016, 7, 154; doi:10.3390/f7080154 www.mdpi.com/journal/forests
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