Jarmo Mäkelä was leading the work on a paper1, published in Geophysical Model Development, where six different formulations for stomatal conductance were optimized with a Monte Carlo style approach. This study was done at 10 boreal coniferous sites, where four sites were used only for validation. The point here is to see, whether the optimization effects the performances of the different conductance formulations, how general are the optimized values between different sites and does Hyytiälä 2006 drought need separate parametrization.
The success of the conductance formulations was very similar as with Jürgen Knauer’s earlier work2, where he was experimenting these same formulations for FLUXNET data. The same parameter set resulted in good results for all the sites. For the drought event in Hyytiälä, most of the conductance models got different parameter values than during normal conditions. The only exception was the unified stomatal optimisation model (USO)3, which got similar optimized parameter values in both conditions.
This is pretty interesting. In principle, we aim to have models that represent the physics and physiology mechanistically, so that the model should give good predictions in all conditions. But in practice, modelling of stomatal conductance is semi-empirical and these models have been developed in pretty regular conditions. So, they might not give good predictions for extreme events. Even though that is something that is needed.
I think it’s cool work, and time is rolling for Jarmo to justify the work in his defense. It’s gonna be great.
1Mäkelä, J., Knauer, J., Aurela, M., Black, A., Heimann, M., Kobayashi, H., Lohila, A., Mammarella, I., Margolis, H., Markkanen, T., Susiluoto, J., Thum, T., Viskari, T., Zaehle, S., and Aalto, T.: Parameter calibration and stomatal conductance formulation comparison for boreal forests with adaptive population importance sampler in the land surface model JSBACH, Geosci. Model Dev., 12, 4075–4098, https://doi.org/10.5194/gmd-12-4075-2019, 2019.
2Knauer, J., Werner, C., and Zaehle, A.: Evaluating stomatal models and their atmospheric drought response in a land surface scheme: A multibiome analysis, J. Geophys. Res.-Biogeosci., 120, 1894–1911, https://doi.org/10.1002/2015JG003114, 2015.
3Medlyn, B., Duursma, R., Eamus, D., Ellsworth, D., Prentice, I., Barton, C., Crous, K., De Angelis, P., Freeman, M., and Wingate, L.: Reconciling the optimal and empirical approaches to modelling stomatal conductance, Global Change Biol., 17, 2134–2144, https://doi.org/10.1111/j.1365-2486.2010.02375.x, 2011.