| Autor: |
Oliver, Rebecca J., Mercado, Lina M., Clark, Doug B., Huntingford, Chris, Taylor, Christopher M., Vidale, Pier Luigi, McGuire, Patrick C., Todt, Markus, Folwell, Sonja, Semeena, Valiyaveetil Shamsudheen, Medlyn, Belinda E. |
| Předmět: |
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| Zdroj: |
Geoscientific Model Development Discussions; 3/14/2022, p1-41, 41p |
| Abstrakt: |
Carbon and water cycle dynamics of vegetation are controlled primarily by photosynthesis and stomatal conductance. Our goal is to improve the representation of these key physiological processes within the JULES land surface model, with a particular focus on refining the temperature sensitivity of photos ynthesis, impacting modelled carbon, energy and water fluxes. We test (1) an imp lementation of the Farquhar et al. (1980) photosynthesis scheme and associated p lant functional type-dependent photosynthetic temperature response functions, (2 ) the optimality-based scheme from Medlyn et al. (2011), and (3) the Kattge and Knorr (2007) photosynthetic capac ity thermal acclimation scheme. New parameters for each model configuration are adopted from recent large observational datasets that synthesise global experime ntal data. These developments to JULES incorporate current physiological underst anding of vegetation behaviour into the model, and enable users to derive direct links between model parameters and on-going measurement campaigns that refine s uch parameter values. Replacement of the original Collatz et al. (1991) photosynthesis model with the Farquhar scheme results in large changes in GPP for current-day, with -10 % reduction in seasonal (June-August; JJA and December-February; DJF) mean GPP in tropical forests, and -20 % increase in the northern high latitude forests in JJA. The optimalit y-based model decreases the latent heat flux for the present-day (-10 %, with an associated increase in sensible heat flux) across regions dominated by needleleaf evergreen forest in the northe rn hemisphere summer. Thermal acclimation of photosynthesis coupled with the Med lyn scheme reduced tropical fores t GPP by up to 5 %, and increased GPP in the high northern latitude forests by b etween 2 to 5 %. Evaluation of simulated carbon and water fluxes by each model c onfiguration against global data products show this latter configuration generat es improvements in these key areas. Thermal acclimation of photosynthesis couple d with the Medlyn scheme improved modelled carbon fluxes in tropical and high northern latitude forests in JJA, a nd improved the simulation of evapotranspiration across much of the northern hem isphere in JJA. Having established good model performance for the contemporary p eriod, we force this new version of JULES offline with a future climate scenario corresponding to rising atmospheric greenhouse gases (SSP5 RCP8.5). In particul ar, these calculations allow understanding of the effects of long-term warming. We find that the impact of thermal acclimation coupled with the optimality-based ; model on simulated fluxes increases latent heat flux (+50 %) by year 2050 compared to the JULES model configuration without acclimation. This new JULES configuration also projects increased GP P across tropical (+10 %) and northern latitude regions (+30 %) by 2050. We conc lude that thermal acclimation of photosynthesis with the Farquhar photosynthesis scheme and the new optimality-based scheme together improve the simulation of carbon and water fluxes for curren t-day, and has a large impact on modelled future carbon cycle dynamics in a warm ing world. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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