Transient State Analysis of Rainfall Infiltration Into Layered Vegetated Soils

Vegetation plays a pivotal role in altering the hydraulic properties of soils, and its effect is stemmed from plant transpiration and also undermined by rainfall. As for the intricate transient behavior of vegetated soils under rainfall, many extant studies either presumed homogeneous soil properties or concentrated on a steady‐state analysis, neglecting the moisture distribution with time in layered vegetated soils. This study proposes a transient analytical model for rainfall infiltration in layered vegetated soils based on Richard's equation. This model is developed by incorporating a depth‐dependent root water uptake sink term and utilizing variable substitution, separation of variables, and the transfer matrix method to derive the pore water pressure (PWP) distribution across different soil layers. The results calculated from the proposed model coincide with those from numerical simulations, with a maximum error of 2.5% in negative PWP in the case study, demonstrating the robustness of this model. Moreover, a parametric study is performed for a better understanding of the impacts of rainfall intensity, thickness of vegetated soil, and transpiration rate on the hydraulic properties of layered vegetated soils. This study well addresses the gap in transient analytical solutions of rainfall infiltration into layered vegetated soils and provides a benchmark for related numerical models.