| 26 May 2026
Development and evaluation of the ECHAM6-iMAPLE v1.0 coupled atmosphere-ecosystem model
Abstract. Land-atmosphere interactions play a fundamental role in regulating climate variability, ecosystem productivity, and air quality through coupled exchanges of energy, water, carbon, and reactive trace gases. However, many Earth system models adopt simplified representations of vegetation physiological processes, leading to biases in terrestrial carbon and water fluxes and increased uncertainties in climate simulations. Here, we present ECHAM6-iMAPLE v1.0, a newly coupled modeling framework that integrates the interactive Model for Air Pollution and Land Ecosystems (iMAPLE v1.0) into the ECHAM6 atmospheric general circulation model. The coupled model is evaluated against reanalysis, benchmark, and satellite datasets. Compared with the original configuration, ECHAM6-iMAPLE substantially improves simulations of gross primary productivity, evapotranspiration, and leaf area index, capturing their spatial distributions and seasonal cycles more reasonably. These improvements arise from well-constrained physiological parameters calibrated using extensive site-level observations and a more realistic representation of key biophysical processes in iMAPLE. With improved carbon and water fluxes, simulations of soil temperature, soil moisture, and surface air temperature show reduced root mean square errors. Overall, evaluations demonstrate that ECHAM6-iMAPLE provides a useful tool for investigating atmosphere-ecosystem interactions and their implications for future climate change projections.
This manuscript presents and evaluates a new model framework that integrates the widely used ECHAM6 atmospheric general circulation model with the dynamic vegetation model iMAPLE. The evaluation compares simulated carbon and water fluxes and other variables such as soil temperature and moisture against observational benchmarks as well as against the ECHAM6 model coupled with the land surface model JSBACH.
While the manuscript itself is well presented and the figures are overall of good quality, I would argue that the manuscript requires substantial revision and restructuring before it can be published. The following main points would need to be addressed:
1) As noted by the authors, both JSBACH and iMAPLE have already been extensively evaluated within the Global Carbon Budget (GCB) framework (the latest version being Friedlingstein et al. 2026, Figure S11), with results also publicly available online. The GCB2025 effort evaluates the same variables, using mostly the same benchmarks and evaluation metrics. It is thus unclear what gap this study fills other than repeating this analysis (at least for carbon and water fluxes as well as LAI). The key difference is that both models here were coupled to ECHAM6, whereas GCB2025 evaluates the model ‘offline’ (i.e. using a common, prescribed forcing). The manuscript should therefore clearly articulate what coupling to the atmosphere changes and what additional insight is gained. I recommend restructuring the paper to focus more explicitly on coupling effects, as partially illustrated in Figures 5 and 6.
2) Related to this, the Methods section needs to better reflect the Results. It is unclear why the Methods description focuses on photosynthesis even though this is the same as in the offline models, which have already been evaluated. The Methods should focus more on the coupling aspect of the model, i.e. addressing the question of how land-atmosphere feedbacks differ between the models and what effects this has on soil moisture, temperature, and other variables.
3) Paper framing: in addition to the points above, both the abstract and the introduction would need to make clear that this manuscript is not just about an evaluation of ECHAM6-iMAPLE but also, in large parts, a comparison with ECHAM6-JSBACH. It is a bit surprising that JSBACH is mentioned fairly late in the manuscript (section 2.1.2).Â
Â
4) Benchmark datasets, particularly MERRA-2, need to be described in more detail. For example, how is soil moisture calculated in MERRA-2 and what assumptions are made? In addition, details on the simulation setup is required to ensure reproducibility of the analysis.
Â
References:
Friedlingstein et al. (2026) Global Carbon Budget 2025, Earth Syst. Sci. Data, 18, 3211–3288, https://doi.org/10.5194/essd-18-3211-2026.