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.