Preprints
https://doi.org/10.5194/gmd-2022-126
https://doi.org/10.5194/gmd-2022-126
Submitted as: development and technical paper
29 Jun 2022
Submitted as: development and technical paper | 29 Jun 2022
Status: this preprint is currently under review for the journal GMD.

Accelerated photosynthesis routine in LPJmL4

Jenny Niebsch1, Werner von Bloh2, Kirsten Thonicke2, and Ronny Ramlau1 Jenny Niebsch et al.
  • 1RICAM, Altenbergerstr. 69, 4040 Linz, Austria
  • 2Potsdam Institute for Climate Impact Research (PIK), Member of the Leibniz Association, 14412 Potsdam, Germany

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.

Jenny Niebsch et al.

Status: open (until 30 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-126', Anonymous Referee #1, 12 Jul 2022 reply

Jenny Niebsch et al.

Jenny Niebsch et al.

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Short summary
The impacts of climate change require strategies for climate adaptation. Dynamic Global Vegetation Models (DGVMs) are used to study the effects of multiple processes in the biosphere under climate change.There is a demand for a better computational performance of the models. In this paper, the photosynthesis model in the Lund-Potsdam-Jena managed Land DGVM (4.0.002) was examined. We found a better numerical solution of a nonlinear equation. A significant run time reduction was possible.