Spatial Variability of Soil Moisture in a Forest Catchment: Temporal Trend and Contributors

Abstract

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 km 2 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.

Role of time variant and invariant terms on soil moisture spatio‐temporal variability in a subhumid coastal wetland

“…In general, the time‐invariant term, M tn , had the most considerable contribution to the total variance of S tn (Figure 4), as previously observed in other studies (Brocca et al, 2014; Dari et al, 2019; Gao et al, 2015; Mittelbach & Seneviratne, 2012; Peng et al, 2016; Wu et al, 2020). The contribution of the time‐invariant component was primarily dependent on season or, more specifically, on soil moisture conditions.…”

“…This study investigates the relative contributions of dynamic and static components to the spatial and temporal soil moisture variability in a wetland area in an arid climate through the analysis of the first and second order statistical moments. Compared to previous studies (Brocca et al, 2014; Dari et al, 2019; Mittelbach & Seneviratne, 2012; Peng et al, 2016; Rötzer et al, 2015; Wu et al, 2020), the present study is applied at a different scale, involving a considerably smaller area, e.g. representing an average area of 25 km 2 per site., in a dryer climate where groundwater is an important control level on soil moisture dynamics.…”

“…Those results raised significant awareness with important implications for understanding and applying the spatio‐temporal features of soil moisture relevant in the validation of spatial soil moisture satellite retrievals and climate and hydrological modelling. Few studies have addressed this issue (Brocca et al, 2014; Dari et al, 2019; Gao et al, 2015; Mittelbach & Seneviratne, 2012; Peng et al, 2016; Wu et al, 2020) and further research is needed covering different scales and conditions.…”

Plant functional trait response to environmental drivers across European temperate forest understorey communities

“…We expected soil moisture to influence community trait responses (Riegal et al, ; Schaffers & Sýkora, ). We used a proxy that integrates the moisture conditions typically experienced in the plot, since in situ measurements are subject to fluctuation from local weather conditions and fine‐scale spatio‐temporal variation (Kopecký & Čížková, ; Korres et al, ; Peng et al, ). We calculated a presence/absence‐based mean community Ellenberg Indicator Value (EIV) score from all the vegetation, including tree, shrub and understorey species, in the plot ( i.e.…”

Environmental and physiological controls on sap flow in a subhumid mountainous catchment in North China

“…This study focuses on the environmental and physiological controls on the sap flow in the subhumid earth-rocky mountainous region of North China, which has pronounced environmental specificities in hydro-climatic conditions, bedrock properties and edaphic features (Peng et al, 2016;Sun et al, 2014;Zhao et al, 2015). The rainfall is moderate (∼600 mm year −1 ) and concentrated in summer, a typical characteristic of monsoon-influenced climate.…”