Characterizing scale specific depth persistence of soil water content along two landscape transects

- MEMD identified dominant scales of spatial SWC variation along two transects.
- Dominant spatial variation scales were at 376 and 677 m; and at 639 and 1304 m.
- Depth persistence of SWC was scale dependent and strongest at the dominant scales.
- Higher degrees of landscape fragmentation resulted in weaker depth persistence.
- During recharge periods, weaker depth persistence occurred in the fragmented transect.

SummaryInformation on depth persistence of soil water content (SWC) is useful for adopting data assimilation techniques in integrating remote sensing data and soil water modeling. The objective of this study was to investigate the scale- and season-specific depth persistence of 0-1.0 m SWC distribution in two transects (having different soils and plant cover) in a watershed on the Chinese Loess Plateau, by combining multivariate empirical mode decomposition (MEMD) with Spearman's rank correlation analysis. Three or four intrinsic mode functions (IMFs) representing specific scales were separated out for SWC of each soil layer. The dominant scales in terms of explaining the spatial variance of SWC for Transect 1 were about 376 m (IMF1) and 677 m (IMF2), and those for Transect 2 were about 639 m (IMF2) and 1304 m (IMF3). Depth persistence of SWC varied with scale, and was the strongest at the dominant scales. The multi-scale depth persistence was weaker along Transect 1 than along Transect 2 due to the higher degree of landscape fragmentation resulting from greater human activity along Transect 1. Weaker depth persistence at each scale was mainly observed at wet conditions for Transect 1. Strong season-related depth persistence was also mainly observed at the dominant scales for both transects. The results of this study are useful for developing sampling strategies for soil water measurements, since information about depth persistence reduces the efforts involved in measuring SWC in deeper layers.