Experimental and Numerical Investigation of the Characteristic Length Governing Soil Evaporation in Layered Sands

Abstract In arid and semi‐arid regions, ecosystems exist with shallow water tables, where evaporation is a key component of the water balance. However, systematically addressing soil evaporation remains challenging due to differing interpretations of the mechanisms that control it. We conducted a laboratory‐scale experimental study to investigate how sand texture, both in homogeneous columns and in layered configurations, affects soil evaporation and the associated characteristic lengths. We analyzed the temporal evolution of evaporation rates in columns of coarse sand, medium‐coarse sand, medium‐fine sand, and fine sand. Our experiments include a wide range of stratified sand configurations (varying in texture, layer thickness, and layering sequence), which extends beyond the limited number of two‐layer systems commonly examined in previous laboratory studies. Our results reveal that, in stratified columns with contrasting textures, the surface layer—whether composed of coarse or fine sand—plays the dominant role in controlling the evaporation response. For example, a coarse sand surface layer over fine sand reduced the duration of the first evaporation stage by two‐thirds and decreased cumulative evaporation by approximately half compared to the homogeneous fine sand column. In contrast, the opposite effect was observed in the coarse sand columns with a fine sand surface layer. By integrating experimental results with numerical solutions, we assessed the impact of the soil characteristic length on soil evaporation using two analytical models. While evaporation losses from heterogeneous surfaces cannot be estimated by averaging the individual material properties, we determined an equivalent characteristic length for the entire system that enables estimation of the overall behavior of the evaporation process in multilayered systems.