Abstract
Abstract. Vegetation plays an important role in regulating global carbon cycles and is a key component of the Earth system models (ESMs) that aim to project Earth's future climate. In the last decade, the vegetation component within ESMs has witnessed great progress from simple “big-leaf” approaches to demographically structured approaches, which have a better representation of plant size, canopy structure, and disturbances. These demographically structured vegetation models typically have a large number of input parameters, and sensitivity analysis is needed to quantify the impact of each parameter on the model outputs for a better understanding of model behavior. In this study, we conducted a comprehensive sensitivity analysis to diagnose the Community Land Model coupled to the Functionally Assembled Terrestrial Simulator, or CLM4.5(FATES). Specifically, we quantified the first- and second-order sensitivities of the model parameters to outputs that represent simulated growth and mortality as well as carbon fluxes and stocks for a tropical site with an extent of 1×1∘. While the photosynthetic capacity parameter (Vc,max25) is found to be important for simulated carbon stocks and fluxes, we also show the importance of carbon storage and allometry parameters, which determine survival and growth strategies within the model. The parameter sensitivity changes with different sizes of trees and climate conditions. The results of this study highlight the importance of understanding the dynamics of the next generation of demographically enabled vegetation models within ESMs to improve model parameterization and structure for better model fidelity.
Highlights
Earth system models (ESMs) are abstract representations of nature used to simulate physical, chemical, and biological processes across the interacting domains of the Earth system to estimate past, present, and future climate (Claussen et al, 2002; Dunne et al, 2012; Arora et al, 2013; Hurrell et al, 2013)
The vegetation model FATES is developed from the ecosystem demography (ED) model, which scales up the behavior of forest ecosystems by aggregating individual trees into representative “cohorts” based on their size and plant functional types (PFTs), and by aggregating groups of cohorts into representative “patches” that explicitly tracks the time between disturbances (Moorcroft et al, 2001)
We highlight the outputs of CLM4.5(FATES) from the 5000 simulations obtained for the Fourier amplitude sensitivity test (FAST) analysis and show the important parameters that control variance in the outputs
Summary
Earth system models (ESMs) are abstract representations of nature used to simulate physical, chemical, and biological processes across the interacting domains of the Earth system to estimate past, present, and future climate (Claussen et al, 2002; Dunne et al, 2012; Arora et al, 2013; Hurrell et al, 2013). A number of vegetation models that can represent plant demographic processes have emerged to better capture coexistence and competition driven by light competition between different sizes of trees within a vertical canopy structure at different successional stages (Moorcroft et al, 2001; Thonicke et al, 2001; Sitch et al, 2003; Hickler et al, 2004; Fisher et al, 2010; Scheiter et al, 2013; Fisher et al, 2018). Drought deciduous threshold Phenology coefficient a Phenology coefficient b Phenology coefficient c Chilling day temperature Cold day temperature Cold days for leaf drop-off Minimum days before leaf on Minimum days before leaf drops Seed turnover Germination rate ed_phdrought−threshold ed_pha ed_phb ed_phc ed_phchiltemp ed_phcoldtemp ed_phncolddayslim ed_phmindayson ed_phdoff−time seed_turnover germination_timescale (0–1) (–) (–)
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