Abstract
Abstract. The dynamic global vegetation model LPJmL4 is a process-based model that simulates climate and land use change impacts on the terrestrial biosphere, agricultural production, and the water and carbon cycle. Different versions of the model have been developed and applied to evaluate the role of natural and managed ecosystems in the Earth system and the potential impacts of global environmental change. A comprehensive model description of the new model version, LPJmL4, is provided in a companion paper (Schaphoff et al., 2018c). Here, we provide a full picture of the model performance, going beyond standard benchmark procedures and give hints on the strengths and shortcomings of the model to identify the need for further model improvement. Specifically, we evaluate LPJmL4 against various datasets from in situ measurement sites, satellite observations, and agricultural yield statistics. We apply a range of metrics to evaluate the quality of the model to simulate stocks and flows of carbon and water in natural and managed ecosystems at different temporal and spatial scales. We show that an advanced phenology scheme improves the simulation of seasonal fluctuations in the atmospheric CO2 concentration, while the permafrost scheme improves estimates of carbon stocks. The full LPJmL4 code including the new developments will be supplied open source through https://gitlab.pik-potsdam.de/lpjml/LPJmL. We hope that this will lead to new model developments and applications that improve the model performance and possibly build up a new understanding of the terrestrial biosphere.
Highlights
The terrestrial biosphere is a central element in the Earth system supporting ecosystem functioning and providing food to human societies
2 Model benchmark In the following we describe in detail the model benchmarking scheme employed here, which allows for a consistent evaluation of processes simulated by LPJmL4 at seasonal and annual resolution and at spatial scales from site level to global level
3 Results and discussion In the following we compare the standard version LPJmL4, which refers to the experiment LPJmL4-growing season index (GSI)-GlobFIRM
Summary
The terrestrial biosphere is a central element in the Earth system supporting ecosystem functioning and providing food to human societies. 2.2 Evaluation datasets Following Kelley et al (2013) we compare LPJmL4 simulations against independent data for vegetation cover, atmospheric CO2 concentrations, carbon stocks and fluxes, fractional burnt area, river discharge, and FAPAR. To the site-based GPP data from Luyssaert et al (2007), we compare spatial patterns and grid-cell-specific GPP simulations to the GPP dataset of Jung et al (2011), as suggested by Kelley et al (2013) This global dataset is based on a larger set of eddy flux tower measurements than the dataset of Luyssaert et al (2007), but uses additional satellite and climate data and empirical modelling for extrapolation to full global coverage. For an overview of all metrics used, see Table 1
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