An event‐based simulation model of moisture and energy fluxes at a bare soil surface

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Abstract
Land surface energy and water balances can be calculated by solving the partial differential equations governing vertical water and heat flow in the soil. Solution methodologies relying on standard discretization procedures are computationally intensive and are therefore poorly suited for long‐term‐simulations or Monte‐Carlo simulations. As an alternative,a certain degree of accuracy may be forfeited in exchange for great reductions in computational effort by using an event‐based simulation model. Since it uses closed‐form solutions of the governing equations as basic building blocks, the event‐based model avoids most of the work associated with discretization. The use of time condensation and simplified soil moisture kinematics allows these closed‐form solutions to serve in continuous simulations under randomly varying forcing. A modified force‐restore model of soil temperature provides the necessary link between the energy and water balances. In comparison with finite element solutions of a detailed set of partial differential equations governing water and heat transport in soil, the event‐based model closely reproduced average energy and water balances and surface temperatures and decreased computational effort by a factor of at least a hundred.