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Abstract:
Terrestrial ecosystem models used for Earth system
modelling show a significant divergence in future patterns
of ecosystem processes, in particular the net land–
atmosphere carbon exchanges, despite a seemingly common
behaviour for the contemporary period. An in-depth evaluation
of these models is hence of high importance to better
understand the reasons for this disagreement.
Here, we develop an extension for existing benchmarking
systems by making use of the complementary information
contained in the observational records of atmospheric CO2
and remotely sensed vegetation activity to provide a novel set
of diagnostics of ecosystem responses to climate variability
in the last 30 yr at different temporal and spatial scales. The
selection of observational characteristics (traits) specifically
considers the robustness of information given that the uncertainty
of both data and evaluation methodology is largely
unknown or difficult to quantify.
Based on these considerations, we introduce a baseline
benchmark – a minimum test that any model has to pass – to
provide a more objective, quantitative evaluation framework.
The benchmarking strategy can be used for any land surface
model, either driven by observed meteorology or coupled to
a climate model.
We apply this framework to evaluate the offline version
of the MPI Earth System Model’s land surface scheme JSBACH.
We demonstrate that the complementary use of atmospheric
CO2 and satellite-based vegetation activity data
allows pinpointing of specific model deficiencies that would not be possible by the sole use of atmospheric CO2 observations.
