The CAP Optimisation Hypothesis Provides Improved Formulations for Stomatal Conductance and Photosynthesis in JSBACH

2021 ◽  
Author(s):  
Aleksanteri Mauranen ◽  
Jarmo Mäkelä ◽  
Teemu Hölttä ◽  
Yann Salmon ◽  
Timo Vesala
Keyword(s):  
Stomatal Conductance ◽  
Land Surface ◽  
Water Status ◽  
Carbon Assimilation ◽  
Land Surface Model ◽  
Photosynthesis Rate ◽  
Climate Forcing ◽  
Surface Model ◽  
Eddy Covariance Measurements ◽  
Semi Empirical

<p>Stomatal conductance formulations are of great importance to how land surface models predict carbon assimilation and transpiration in vegetation. In this study, novel stomatal conductance formulations based on the CAP optimisation hypothesis (Dewar et al. 2018) are implemented in the land surface model JSBACH. Besides new stomatal conductance functions, the CAP framework enables a computational streamlining of the resolution of photosynthesis rate and leaf internal CO<sub>2</sub> concentration.</p><p>The formulations are based on the CAP optimisation hypothesis coupled to different photosynthesis models. Models constructed this way incorporate non-stomatal limitations to photosynthesis through the coupling of carbon assimilation to the soil-to-leaf hydraulic pathway. This entails a direct link from soil water status to stomatal conductance, photosynthesis rate and leaf internal CO<sub>2 </sub>concentration. While this construction does away with the need for some previous fitted or empirical parameters, new parameters are required to represent xylem hydraulic conductance and downregulation of photosynthesis during drought stress.</p><p>These new models are compared to the widely used USO stomatal conductance model (Medlyn et al. 2011). A standalone version of JSBACH is run for single grid cells representing two boreal Scots pine (<em>Pinus sylvestris</em>) dominated sites in Finland (Hyytiälä and Sodankylä). Climate forcing is done with FLUXNET data from 2001 through 2012 and observations are from eddy covariance measurements from the two sites.</p><p>Preliminary results indicate that some of the new formulations give reasonable results. This is very promising, since they are more detailed and theoretically robust than their semi-empirical predecessors, yet streamline the computational process.</p><p>References:<br>Dewar et al. 2018, <em>New Phytol. </em>217: 571–581<br>Medlyn et al. 2011, <em>Glob. Change Biol.</em> 17: 2134–2144</p>

scholarly journals Observed nighttime conductance alters modeled global hydrology and carbon budgets

2015 ◽  
Vol 8 (12) ◽  
pp. 10339-10363 ◽  
Author(s):  
D. L. Lombardozzi ◽  
M. J. B. Zeppel ◽  
R. A. Fisher ◽  
A. Tawfik
Keyword(s):  
Stomatal Conductance ◽  
Land Surface ◽  
Arid Regions ◽  
Land Surface Model ◽  
Carbon Gain ◽  
Surface Model ◽  
Land Surface Models ◽  
Climate Simulations ◽  
Surface Models ◽  
Semi Arid

Abstract. The terrestrial biosphere regulates climate through carbon, water, and energy exchanges with the atmosphere. Land surface models estimate plant transpiration, which is actively regulated by stomatal pores, and provide projections essential for understanding Earth's carbon and water resources. Empirical evidence from 204 species suggests that significant amounts of water are lost through leaves at night, though land surface models typically reduce stomatal conductance to nearly zero at night. Here, we apply observed nighttime stomatal conductance values to a global land surface model, to better constrain carbon and water budgets. We find that our modifications increase transpiration up to 5 % globally, reduce modeled available soil moisture by up to 50 % in semi-arid regions, and increase the importance of the land surface on modulating energy fluxes. Carbon gain declines up to ~ 4 % globally and > 25 % in semi-arid regions. We advocate for realistic constraints of minimum stomatal conductance in future climate simulations, and widespread field observations to improve parameterizations.

scholarly journals Parameter Sensitivity of the Noah-MP Land Surface Model with Dynamic Vegetation

2018 ◽  
Vol 19 (5) ◽  
pp. 815-830 ◽  
Author(s):  
Kristi R. Arsenault ◽  
Grey S. Nearing ◽  
Shugong Wang ◽  
Soni Yatheendradas ◽  
Christa D. Peters-Lidard
Keyword(s):  
Dynamic Simulation ◽  
Land Surface ◽  
Carbon Assimilation ◽  
Land Surface Model ◽  
Net Ecosystem Exchange ◽  
Primary User ◽  
Soil Parameters ◽  
Surface Model ◽  
Carbon Decomposition ◽  
Decomposition Processes

Abstract The Noah land surface model with multiple parameterization options (Noah-MP) includes a routine for the dynamic simulation of vegetation carbon assimilation and soil carbon decomposition processes. To use remote sensing observations of vegetation to constrain simulations from this model, it is necessary first to understand the sensitivity of the model to its parameters. This is required for efficient parameter estimation, which is both a valuable way to use observations and also a first or concurrent step in many state-updating data assimilation procedures. We use variance decomposition to assess the sensitivity of estimates of sensible heat, latent heat, soil moisture, and net ecosystem exchange made by certain standard Noah-MP configurations that include the dynamic simulation of vegetation and carbon to 43 primary user-specified parameters. This is done using 32 years’ worth of data from 10 international FluxNet sites. Findings indicate that there are five soil parameters and six (or more) vegetation parameters (depending on the model configuration) that act as primary controls on these states and fluxes.

scholarly journals A test of an optimal stomatal conductance scheme within the CABLE land surface model

2015 ◽  
Vol 8 (2) ◽  
pp. 431-452 ◽  
Author(s):  
M. G. De Kauwe ◽  
J. Kala ◽  
Y.-S. Lin ◽  
A. J. Pitman ◽  
B. E. Medlyn ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Land Surface ◽  
Model Performance ◽  
Land Surface Model ◽  
Surface Model ◽  
Model Parameters ◽  
Plant Water ◽  
Plant Water Use ◽  
Bioclimatic Variables ◽  
Small Model

Abstract. Stomatal conductance (gs) affects the fluxes of carbon, energy and water between the vegetated land surface and the atmosphere. We test an implementation of an optimal stomatal conductance model within the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model (LSM). In common with many LSMs, CABLE does not differentiate between gs model parameters in relation to plant functional type (PFT), but instead only in relation to photosynthetic pathway. We constrained the key model parameter "g1", which represents plant water use strategy, by PFT, based on a global synthesis of stomatal behaviour. As proof of concept, we also demonstrate that the g1 parameter can be estimated using two long-term average (1960–1990) bioclimatic variables: (i) temperature and (ii) an indirect estimate of annual plant water availability. The new stomatal model, in conjunction with PFT parameterisations, resulted in a large reduction in annual fluxes of transpiration (~ 30% compared to the standard CABLE simulations) across evergreen needleleaf, tundra and C4 grass regions. Differences in other regions of the globe were typically small. Model performance against upscaled data products was not degraded, but did not noticeably reduce existing model–data biases. We identified assumptions relating to the coupling of the vegetation to the atmosphere and the parameterisation of the minimum stomatal conductance as areas requiring further investigation in both CABLE and potentially other LSMs. We conclude that optimisation theory can yield a simple and tractable approach to predicting stomatal conductance in LSMs.

Did the rise of highly-transpiring angiosperms influenced Cretaceous climate ? A modelling approach with the IPSL atmosphere-land surface model.

2020 ◽  
Author(s):  
Julia Bres ◽  
Pierre Sepulchre ◽  
Nicolas Vuichard ◽  
Nicolas Viovy
Keyword(s):  
Stomatal Conductance ◽  
Land Surface ◽  
Fossil Record ◽  
Hydrological Cycle ◽  
Land Surface Model ◽  
Plant Evolution ◽  
Surface Model ◽  
Vegetation Model ◽  
Leaf Vein ◽  
Modelling Approach

<p><span><span>The Cretaceous angiosperm radiation was a major event for terrestrial plant evolution, and flowering plants represent more than 94 % of present-day plant diversity. The fossil record shows that angiosperm leaf vein densities reached particularly high values (> 12 mm/mm</span></span><sup><span><span>2</span></span></sup><span><span>)</span></span> <span><span>between the </span></span><span>Albian and the Cenomanian (108–94 Ma) </span><span><span>compared to gymnosperms (~ 2.5 mm/mm</span></span><sup><span><span>2</span></span></sup><span><span>). Empirical models</span></span> <span><span>also suggest that stomatal conductance to water vapour increases as a response to higher leaf vein densities. How much do this shift to higher values of stomatal conductance have modified the continental transpiration budget,</span></span> <span><span>and ultimately global hydrological cycle ? To address this question we used the IPSL coupled atmosphere-vegetation model forced by Cretaceous boundary conditions, and built plant functional types including</span></span> <span><span>stomatal conductance values consistent with the fossil record. We quantify the transpiration fluxes through different sensitivity experiments and explore the vegetation-atmosphere feedbacks and their impact on the Cretaceous climate.</span></span></p>

scholarly journals A test of an optimal stomatal conductance scheme within the CABLE Land Surface Model

2014 ◽  
Vol 7 (5) ◽  
pp. 6845-6891 ◽  
Author(s):  
M. G. De Kauwe ◽  
J. Kala ◽  
Y.-S. Lin ◽  
A. J. Pitman ◽  
B. E. Medlyn ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Land Surface ◽  
Model Performance ◽  
Land Surface Model ◽  
Surface Model ◽  
Model Parameters ◽  
Bioclimatic Variables ◽  
Small Model ◽  
Land Exchange

Abstract. Stomatal conductance (gs) affects the fluxes of carbon, energy and water between the vegetated land surface and the atmosphere. We test an implementation of an optimal stomatal conductance model within the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model (LSM). In common with many LSMs, CABLE does not differentiate between gs model parameters in relation to plant functional type (PFT), but instead only in relation to photosynthetic pathway. We therefore constrained the key model parameter "g1" which represents a plants water use strategy by PFT based on a global synthesis of stomatal behaviour. As proof of concept, we also demonstrate that the g1 parameter can be estimated using two long-term average (1960–1990) bioclimatic variables: (i) temperature and (ii) an indirect estimate of annual plant water availability. The new stomatal models in conjunction with PFT parameterisations resulted in a large reduction in annual fluxes of transpiration (~ 30% compared to the standard CABLE simulations) across evergreen needleleaf, tundra and C4 grass regions. Differences in other regions of the globe were typically small. Model performance when compared to upscaled data products was not degraded, though the new stomatal conductance scheme did not noticeably change existing model-data biases. We conclude that optimisation theory can yield a simple and tractable approach to predicting stomatal conductance in LSMs.

scholarly journals Representing nighttime and minimum conductance in CLM4.5: global hydrology and carbon sensitivity analysis using observational constraints

2017 ◽  
Vol 10 (1) ◽  
pp. 321-331 ◽  
Author(s):  
Danica L. Lombardozzi ◽  
Melanie J. B. Zeppel ◽  
Rosie A. Fisher ◽  
Ahmed Tawfik
Keyword(s):  
Stomatal Conductance ◽  
Land Surface ◽  
Arid Regions ◽  
Land Surface Model ◽  
Carbon Gain ◽  
Surface Model ◽  
Land Surface Models ◽  
Community Land Model ◽  
Surface Models ◽  
Semi Arid

Abstract. The terrestrial biosphere regulates climate through carbon, water, and energy exchanges with the atmosphere. Land-surface models estimate plant transpiration, which is actively regulated by stomatal pores, and provide projections essential for understanding Earth's carbon and water resources. Empirical evidence from 204 species suggests that significant amounts of water are lost through leaves at night, though land-surface models typically reduce stomatal conductance to nearly zero at night. Here, we test the sensitivity of carbon and water budgets in a global land-surface model, the Community Land Model (CLM) version 4.5, to three different methods of incorporating observed nighttime stomatal conductance values. We find that our modifications increase transpiration by up to 5 % globally, reduce modeled available soil moisture by up to 50 % in semi-arid regions, and increase the importance of the land surface in modulating energy fluxes. Carbon gain declines by up to  ∼ 4 % globally and  >  25 % in semi-arid regions. We advocate for realistic constraints of minimum stomatal conductance in future climate simulations, and widespread field observations to improve parameterizations.

L'apport de la télédétection spatiale à la modélisation des surfaces continentales

2020 ◽  
pp. 052
Author(s):  
Jean-Christophe Calvet ◽  
Jean-Louis Champeaux
Keyword(s):  
Satellite Data ◽  
Land Surface ◽  
Land Surface Model ◽  
Static Model ◽  
Geographic Information ◽  
Surface Model ◽  
Model Parameters

Cet article présente les différentes étapes des développements réalisés au CNRM des années 1990 à nos jours pour spatialiser à diverses échelles les simulations du modèle Isba des surfaces terrestres. Une attention particulière est portée sur l'intégration, dans le modèle, de données satellitaires permettant de caractériser la végétation. Deux façons complémentaires d'introduire de l'information géographique dans Isba sont présentées : cartographie de paramètres statiques et intégration au fil de l'eau dans le modèle de variables observables depuis l'espace. This paper presents successive steps in developments made at CNRM from the 1990s to the present-day in order to spatialize the simulations of the Isba land surface model at various scales. The focus is on the integration in the model of satellite data informative about vegetation. Two complementary ways to integrate geographic information in Isba are presented: mapping of static model parameters and sequential assimilation of variables observable from space.

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