A study of the water and energy transfer at the soil surface in cropped field on the Loess Plateau of northwestern China

In this study, we tried to model the processes of moisture and heat transfers in the soil–vegetation–atmosphere system in an integrated comprehensive way. The purpose of the study is to simulate profiles of soil water content and temperature at root active zone (i.e., 0–50 cm), taking the root water uptake, soil evaporation, and canopy transpiration into account. The water and heat transfer equations are solved by an iterative Newton–Raphson technique and a finite difference method is used to solve the governing equations. Soil water content and soil temperature dynamics could be simulated rather accurately in a cropped field on Loess Plateau area. The water and heat transfer flux predicted by the classical theory of Philip and de Vries (Tans Am Geophys Union 38:222–232, 1957) slightly overestimated near the surface and underestimated at the deeper depths, as a result of the overestimated soil evaporation at the top soil layer (0–10 cm) and underestimated crop canopy transpiration at the deeper depths (10–50 cm). Water content tended to be underestimated for the entire profile at the soil surface (from 0 to 50 cm). Soil temperatures during the simulated period was slightly overestimated in the nighttimes and underestimated in the daytimes, as a result of the underestimated soil water content at the top soil layer (0–10 cm) and overestimated at the deeper depths (10–50 cm). Soil temperatures tended to be underestimated for the entire profile at the soil surface (from 0 to 50 cm). While the sum of the water and heat regimes yielded a much better match with the soil water content and soil temperature obtained from the field observations. The results obtained show that the model coupled water and heat transfer is able to capture the dynamics of soil water content.