Exploring the feasibility of using the soil temperature to identify preferential and lateral subsurface flows

Soil temperature can be influenced by rapidly infiltrating water. Deviations from a uniform soil heat distribution could result from vertical preferential flow (VPF) and lateral subsurface flow (LSF) events. The objective was to identify the effect of infiltration on the soil temperature time series in a lysimeter with forced vertical movement and that in a sloping field to distinguish between VPF and LSF. Wavelet coherence analysis (WCA) was used to analyze soil temperature time series measured in a Colluvic Regosol close to the surface (15-cm depth) and below (80-cm depth) in a horizon with possible LSF occurrence. The soil temperatures in these depths were correlated at a daily scale reflecting diurnal fluctuations of air temperatures. A correlation at a monthly scale was similar to the periodicity in the wavelet spectrum of the precipitation from May through October 2015. In this period, soil temperatures at 80-cm depth changed faster in the lysimeter than in the field, indicating a dominating infiltration-induced vertical heat movement in the lysimeter. When assuming a temperature-dampening effect in the sloping field soil by laterally moving temperature-equilibrated soil water, observed deviations in soil temperature profiles between lysimeter and field could be indicative for LSF in the field. However, LSF occurrence could only be verified by soil water content measurements for single rainfall events in October and May. The analysis was useful to identify qualitatively relevant events in a time series. For quantitative analysis, soil moisture data need to be considered.

Automated summary

Soil temperature can be influenced by infiltrating water, leading to non-uniform heat distribution. Wavelet coherence analysis is effective in analyzing soil temperature time series. The study found that vertical heat conduction induced by infiltration is faster in lysimeters compared to fields.