Assessing JULES across bioclimatic domains through a Pan-African flux tower evaluation: Insights into controls on gross primary productivity, ecosystem respiration, and evapotranspiration biases
Abstract
Land surface models are fundamental for simulating coupled carbon, water and energy exchanges in Earth system models, yet their performance remains poorly constrained across Africa's diverse hydroclimatic gradients. We evaluate the Joint UK Land Environment Simulator (JULES) using eddy covariance observations from 16 flux towers spanning major African ecosystem types. Model skill is assessed for gross primary productivity (GPP), ecosystem respiration (Reco), and evapotranspiration, and we examine how model bias and error vary along gradients of mean annual temperature, aridity index, and precipitation anomalies. JULES reproduced broad seasonal dynamics of carbon and water fluxes across several ecosystems but showed systematic limitations in simulating Reco and interannual variability of GPP. Model performance differed among ecosystem types, with wetlands exhibiting large model-observation mismatches and cropland sites showing GPP overestimation linked to excessive simulated leaf area index. To isolate environmental controls on performance, we applied linear mixed-effects modeling to partition site-level variability from climate-driven effects. Aridity and precipitation anomalies emerged as dominant predictors of model bias and error, with wetter and anomalously humid conditions associated with larger deviations from observations, indicating limitations in representing soil hydrology and vegetation water stress processes. By integrating an expanded African flux tower network, this study provides a comprehensive regional evaluation of JULES. The results identify hydroclimatic regimes where model development should be prioritized and emphasize the importance of strengthening benchmarking across underrepresented African ecosystems to improve model transferability and support reliable climate and land management decision support under environmental change.
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BibTeX
@article{akhabue2026assessing,
title = {{Assessing JULES across bioclimatic domains through a Pan-African flux tower evaluation: Insights into controls on gross primary productivity, ecosystem respiration, and evapotranspiration biases}},
author = {Enimhien F. Akhabue and Andrew M. Cunliffe and Karina Bett-Williams and Anna B. Harper and Songyan Zhu and Petra Holden and Jonas Ardö and Mika Aurela and Jérôme Demarty and Frédéric C. Do and Jordi Etchanchu and Mangaliso Gondwe and Carole Helfters and Laurent Kergoat and Giacomo Nicolini and Yann Nouvellon and Maria Carolina Duran Rojas and Olivier Roupsard and Torbern Tagesson and Ville Vakkari and Pieter Vanzyl and Aleksander Wieckowski},
journal = {Journal of Advances in Modeling Earth Systems},
year = {2026},
month = oct,
doi = {10.1029/2026ms005888},
url = {https://hal.science/hal-05796363v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Assessing JULES across bioclimatic domains through a Pan-African flux tower evaluation: Insights into controls on gross primary productivity, ecosystem respiration, and evapotranspiration biases
AU - Enimhien F. Akhabue
AU - Andrew M. Cunliffe
AU - Karina Bett-Williams
AU - Anna B. Harper
AU - Songyan Zhu
AU - Petra Holden
AU - Jonas Ardö
AU - Mika Aurela
AU - Jérôme Demarty
AU - Frédéric C. Do
AU - Jordi Etchanchu
AU - Mangaliso Gondwe
AU - Carole Helfters
AU - Laurent Kergoat
AU - Giacomo Nicolini
AU - Yann Nouvellon
AU - Maria Carolina Duran Rojas
AU - Olivier Roupsard
AU - Torbern Tagesson
AU - Ville Vakkari
AU - Pieter Vanzyl
AU - Aleksander Wieckowski
PY - 2026
DA - 2026/10/13
JO - Journal of Advances in Modeling Earth Systems
DO - 10.1029/2026ms005888
UR - https://hal.science/hal-05796363v1
AB - Land surface models are fundamental for simulating coupled carbon, water and energy exchanges in Earth system models, yet their performance remains poorly constrained across Africa's diverse hydroclimatic gradients. We evaluate the Joint UK Land Environment Simulator (JULES) using eddy covariance observations from 16 flux towers spanning major African ecosystem types. Model skill is assessed for gross primary productivity (GPP), ecosystem respiration (Reco), and evapotranspiration, and we examine how model bias and error vary along gradients of mean annual temperature, aridity index, and precipitation anomalies. JULES reproduced broad seasonal dynamics of carbon and water fluxes across several ecosystems but showed systematic limitations in simulating Reco and interannual variability of GPP. Model performance differed among ecosystem types, with wetlands exhibiting large model-observation mismatches and cropland sites showing GPP overestimation linked to excessive simulated leaf area index. To isolate environmental controls on performance, we applied linear mixed-effects modeling to partition site-level variability from climate-driven effects. Aridity and precipitation anomalies emerged as dominant predictors of model bias and error, with wetter and anomalously humid conditions associated with larger deviations from observations, indicating limitations in representing soil hydrology and vegetation water stress processes. By integrating an expanded African flux tower network, this study provides a comprehensive regional evaluation of JULES. The results identify hydroclimatic regimes where model development should be prioritized and emphasize the importance of strengthening benchmarking across underrepresented African ecosystems to improve model transferability and support reliable climate and land management decision support under environmental change.
SN - 1942-2466
ER -