The Spatial and Temporal Variability of Soil-Water Evaporation as Influenced by Near-Surface Soil Porosities

Soil water evaporation rate (E) exhibits significant spatial and temporal variability under field conditions. Some studies demonstrated the influence of porosity (n) on soil-water evaporation processes. Still, the specific mechanisms for n affecting the spatial and temporal variability of E under transient field conditions remain poorly understood. This study addresses this research gap through continuous, high-frequency, millimeter-scale observations of soil temperature, thermal properties, and E dynamics in bare loamy sand and sandy loam soils. Using 11-needle heat pulse sensors, we monitored E on two experimental subplots with high n (H plot) and low n (L plot) treatments. During the observation period, soil evaporation primarily occurred within the 0–21 mm layer in the H plot and 0–15 mm layer in the L plot. Comparative analysis revealed distinct temporal dynamics and spatial progression patterns of E between two plots, despite a 7% n difference in Experiment 1 (n = 0.52 vs. 0.56) and 8% in Experiment 2 (n = 0.47 vs. 0.51). Specifically, in the H plot, the daily peak E consistently occurred earlier and exhibited greater magnitude across all depth increments compared to the L plot. Additionally, the evaporation process persisted longer within each depth increment of the L plot before transitioning to deeper soil layers. Quantitative analysis demonstrated that a 7% increase in n corresponded to an 18% increase in cumulative E. These findings emphasize the importance of considering n variations for accurately modelling and interpreting broader hydrologic and environmental processes.