D8.6: Documentation on the setting up of the offline terrestrial biosphere simulations
Creators: name: Lee, Junhong
name: Hohenegger, Cathy
Publisher: name: Zenodo
Year: 2024

description: About this document

This documentation contains instructions for setting up the JSBACH model forced by the output from storm-resolving models to quantify the carbon fluxes and stocks over Europe.

Work package in charge

WP8

Executive summary

This report presents the deliverable associated with WP8.6, which is about documenting the setup of offline terrestrial biosphere simulations driven by the output of the NextGEMS 5-km ICON model to estimate carbon fluxes and storage. It describes the required land forcing data for vegetation and soil parameters, initial states, and atmospheric forcing data, along with the procedures used to generate the forcing data and to spin up the biosphere model. In particular, the carbon pools need to be spun up, so that the carbon reaches equilibrium with the atmosphere, which can take hundreds to thousands of years, especially for humus pools. To minimize computing time, a separate workflow is used to estimate the equilibrium carbon conditions of humus pools and a downscaling spin-up strategy is developed. The workflow adjusts humus pools based on the analytical prediction of the equilibrium concentration of carbon in humus pools, extrapolating from their transient behaviour. This workflow saves 63.48% of the otherwise required time for spin-up. The downscaling spin-up strategy consists of spinning up the carbon pools first using a grid spacing of 160 km and then of 5 km. But the downscaling spin-up strategy turns out to not reduce the required spin-up time. Hence, we only use the adjusting humus pools workflow and show that we can indeed spin up the carbon pools for a domain the size of Europe, with a grid spacing of 5 km. 473 years are required to complete the spin-up, equivalent to about 3 days of computation using eight nodes of the supercomuter Levante. Finally, a step-by-step tutorial explaining the setup of the offline terrestrial biosphere simulations is provided, with accompanying workflows available at ‘https://gitlab.dkrz.de/m300793/scripts_offline_jsbach.git’. 

Conclusion & Results

This report serves as the deliverable for WP8.6 ”Documentation for setting up offline terrestrial biosphere simulations”, focusing on setting up the offline JSBACH model and spinning up JSBACH using the output from the NextGEMS global storm-resolving ICON model. 

First, we provide an overview of the required land forcing data, atmospheric forcing data, and the process for obtaining these data. Second, we test various spin-up strategies aimed at reducing the time required to spin up the land carbon pools, revealing that i) the workflow to adjust humus pools based on the analytical prediction of the equilibrium concentration of carbon of the humus pools saves 63.48% of the spin-up time, and ii) including a downscaling step by first spinning up a coarser-resolution simulation does not save spin-up time.

Based upon these findings, we set up our final computational domain for offline JSBACH carbon flux simulations as covering Europe (279,900 points), encompassing 28 countries of the European Union and Eastern Europe where dense forests exist. The final grid spacing is 5 km, in agreement with the resolution of ICON. From past studies, carbon pools are considered as spun up when the absolute difference in total ecosystem carbon is less than 1 g C m−2 year−1 at each grid cell. We show that the carbon pools of our simulation are indeed spun up after 473 years (Fig. 8). This required 2.96 days of computation using eight nodes of the supercomputer Levante at DKRZ. The model is ready to be used for the science planned in WP9.4, estimating carbon stocks and fluxes over Europe with the JSBACH model using the output from the NextGEMS global storm-resolving ICON model.