Treffer: Accurate and Efficient Numerical Simulation of Land Models Using SUMMA With SUNDIALS.

Numerical simulation of land models without error control can be highly inaccurate. We present the incorporation of the Suite of Nonlinear and Differential‐Algebraic Equation Solvers (SUNDIALS) package to solve the equations that simulate thermodynamics and hydrologic processes in the Structure for Unifying Multiple Modeling Alternatives (SUMMA) land model. The algorithmic features of SUNDIALS, such as error estimation and adaptive order and step‐size control, result in a SUMMA‐SUNDIALS model that delivers substantially improved accuracy and relative computational efficiency compared to integration with the previous SUMMA model, which uses the low‐order backward Euler method with no rigorous error control. The results are demonstrated through simulations over the North American continent with more than 500,000 spatial elements. Compared to the previous SUMMA model, we find that the simulations produced by the SUMMA‐SUNDIALS model are orders of magnitude closer to converged solutions for the same computational cost. Being able to efficiently perform more reliable simulations makes the SUMMA‐SUNDIALS model a powerful tool for improving our understanding of the terrestrial component of the Earth System. Plain Language Summary: The results produced from numerical simulation of land models can be highly inaccurate unless error control is used. The Suite of Nonlinear and Differential‐Algebraic Equation Solvers (SUNDIALS) is a software package that solves differential and differential‐algebraic equations accurately and efficiently with adaptive time‐steps and order. We use SUNDIALS to solve the equations that simulate thermodynamics and hydrologic processes in the Structure for Unifying Multiple Modeling Alternatives (SUMMA) land model. The resulting SUMMA‐SUNDIALS model delivers substantially improved accuracy and relative computational efficiency compared to integration with the previous SUMMA model, which uses the low‐order backward Euler method and no rigorous error control. The results are demonstrated through simulations over the North American continent with more than 500,000 spatial elements. Compared to the previous SUMMA model, we find that the simulations produced by the SUMMA‐SUNDIALS model are orders of magnitude closer to converged solutions for the same computational cost. Being able to efficiently perform more reliable simulations in an efficient manner makes the SUMMA‐SUNDIALS model a powerful tool for improving our understanding of the terrestrial component of the Earth System. Key Points: Numerical simulation of land models without error control can be highly inaccurateWe have incorporated the Suite of Nonlinear and Differential‐Algebraic Equation Solvers (SUNDIALS) software library into the Structure for Unifying Multiple Modeling Alternatives (SUMMA) modelThe SUMMA simulations using SUNDIALS show large gains in accuracy and efficiency compared to integration without error control [ABSTRACT FROM AUTHOR]

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