An improved understanding of controls of soil moisture dynamics in a small watershed

Abstract

The traditional correlation analysis may misinterpret soil water dynamics controls due to the cross-correlated environmental factors. Techniques to date are limited in their capacity to truly understand the controls of soil water dynamics. The objective of this study was to reveal soil water dynamics controls by empirical orthogonal function (EOF) analysis of the space-variant temporal anomaly (RTN ) of SWC which is responsible for the spatial variability of soil water dynamics. For this purpose, SWC of 0–0.8 m layer in a small watershed on the Chinese Loess Plateau was used. Results indicated that 86% of the total variations of were explained by three significant spatial structures (EOFs). Sand content and grass yield dominated the EOF1 of , and finer soils with greater grass yield were prone to more temporal changes in SWC. Elevation and aspect dominated EOF2 and EOF3 of , respectively. However, their effects on soil water dynamics were time-dependent. This EOF analysis showed that three independent groups of factors (i.e., soil and vegetation dominated earth surface condition, elevation related near surface air humidity, and aspect regulated energy input) may drive the variability in soil water dynamics. Traditional correlation analysis, however, indicated that SWC was greater at higher elevation and sun-facing slopes, which distorted the soil water dynamics controls. Although original SWC-based partial correlation basically supported our findings, the results highly depended on the controlling factors selected. This study confirmed soil and vegetation are dominant controls of soil water dynamics, while the role of topography (i.e., elevation and aspect) cannot be ignored on some dates.