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Abstract:
The increasing impacts of climate change require strategies for climate adaptation. Dynamic Global Vegetation Models (DGVMs) are one type of multi-sectorial impact models with which the effects of multiple interacting processes in the terrestrial biosphere under climate change can be studied. The complexity of DGVMs is increasing as more and more processes, especially for plant physiology, are implemented. Therefore, there is a growing demand for increasing the computational performance of the underlying algorithms as well as ensuring their numerical accuracy. One way to approach this issue is to analyse the routines which have the potential for improved computational efficiency and/or increased accuracy when applying sophisticated mathematical methods.
In this paper, the Farquhar-Collatz photosynthesis model under water stress as implemented in the Lund-Potsdam-Jena managed Land DGVM (4.0.002) was examined. We found that the numerical solution of a nonlinear equation, so far solved with the Bisection method, could be significantly improved by using Newton's method instead. The latter requires the computation of the derivative of the underlying function which is presented. Model simulations show a significant lower number of iterations to solve the equation numerically and an overall run time reduction of the model of about 16 % depending on the chosen accuracy. The Farquhar-Collatz photosynthesis model forms the core component in many DGVMs and land-surface models. An update in the numerical solution of the nonlinear equation can therefore be applied to similar photosynthesis models. Furthermore, this exercise can serve as an example for improving computationally costly routines while improving their mathematical accuracy.
