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Development and Validation of a Numerical Model Simulating Evaporation from Short Cores
Author(s) -
Reynolds W. D.,
Walker G. K.
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800050002x
Subject(s) - evaporation , isothermal process , mechanics , discretization , richards equation , soil science , water content , flux (metallurgy) , water balance , conservation of mass , environmental science , constant (computer programming) , nonlinear system , soil water , mathematics , materials science , thermodynamics , geotechnical engineering , geology , physics , mathematical analysis , computer science , quantum mechanics , metallurgy , programming language
A theoretically‐based assessment of the short core evaporimeter technique for measuring evaporation from the soil surface can be conducted using numerical simulation. As an initial step, a numerical model is developed that simulates evaporation from isothermal, homogeneous, finite soil columns with a specified initial water content profile. Features of this model include nonlinearized solution of the highly nonlinear surface boundary condition, automatic adjustment of time‐step size according to a mass balance criterion, remaximization of program efficiency at each time‐step, and the use of soil surface temperature as the primary forcing function. The validity of the model was established through its ability to realistically simulate the constant and falling rate stages of soil drying, including root‐time behavior, and by its good mass conservation and stability characteristics. Drying of a clay soil with an initial uniform water content of 0.40 cm 3 w cm ‐3 pm for 12 000 min under a constant evaporative demand of 4.4 × 10 −4 cm 3 w cm ‐2 pm min −1 could be simulated with a time‐step size ranging from 10 to 13.7 min, a specific mass (i.e. flux) balance of < 3%, a cumulative mass balance of < 0.3%, and with generally < five iterations per time‐step. A discretization analysis revealed that for the first centimeter below the soil surface a 0.2‐cm nodal spacing was required to obtain accurate estimates of the evaporative flux and the near‐surface water content profile. Below that depth, however, nodal spacing can be greatly increased without serious reduction of accuracy. Successful validation of the model supports extension to field conditions.