Submitted as: model evaluation paper 05 Feb 2021

Submitted as: model evaluation paper | 05 Feb 2021

Review status: this preprint is currently under review for the journal GMD.

Modelling Gas Exchange and Biomass Production in West African Sahelian and Sudanian Ecological Zones

Jaber Rahimi1, Expedit Evariste Ago2,3, Augustine Ayantunde4, Sina Berger1,5, Jan Bogaert3, Klaus Butterbach-Bahl1,6, Bernard Cappelaere7, Jérôme Demarty7, Abdoul Aziz Diouf8, Ulrike Falk9, Edwin Haas1, Pierre Hiernaux10, David Kraus1, Olivier Roupsard11,12,13, Clemens Scheer1, Amit Kumar Srivastava14, Torbern Tagesson15,16, and Rüdiger Grote1 Jaber Rahimi et al.
  • 1Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Garmisch-Partenkirchen, Germany
  • 2Laboratoire d’Ecologie Appliquée, Faculté des Sciences Agronomiques, Université d’Abomey-Calavi, Cotonou, Bénin
  • 3Biodiversity and Landscape Unit, Université de Liège Gembloux Agro-Bio Tech, Gembloux, Belgium
  • 4International Livestock Research Institute (ILRI), Ouagadougou, Burkina Faso
  • 5University of Augsburg, Regional Climate and Hydrology Research Group, Augsburg, Germany
  • 6International Livestock Research Institute (ILRI), Nairobi, Kenya
  • 7HydroSciences Montpellier, Univ. Montpellier, IRD, CNRS, Montpellier, France
  • 8Centre de Suivi Ecologique (CSE), Dakar, Senegal
  • 9Satellite-based Climate Monitoring, Deutscher Wetterdienst (DWD), Offenbach, Germany
  • 10Géosciences Environnement Toulouse (GET), CNRS, IRD, UPS, Toulouse, France
  • 11CIRAD, UMR Eco&Sols, BP1386, CP18524, Dakar, Senegal
  • 12Eco&Sols, Univ Montpellier, CIRAD, INRAE, IRD, Institut Agro, Montpellier, France
  • 13LMI IESOL, Centre IRD-ISRA de Bel Air, BP1386, CP18524, Dakar, Senegal
  • 14Institute of Crop Science and Resource Conservation, University of Bonn, Bonn, Germany
  • 15Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark
  • 16Department of Physical Geography and Ecosystem Sciences, Lund University, Lund, Sweden

Abstract. West African Sahelian and Sudanian ecosystems are providing essential services to people and also play a significant role within the global carbon cycle. However, climate and land use are dynamically changing and it remains uncertain how these changes will affect the potential of these regions for providing food and fodder resources or the biosphere-atmosphere exchange of CO2. In this study, we investigate the capacity of a process-based biogeochemical model, LandscapeDNDC, to simulate net ecosystem exchange (NEE) and aboveground biomass of typical managed and natural Sahelian and Sudanian savanna ecosystems. We tested the model for various sites with different proportions of trees and grasses, as well as for the most typical arable cropping systems of the region. In order to describe the phenological development with a common parameterization across all ecosystem types, we introduced soil-water availability in addition to temperature as a driver as seasonal soil water-shortage is a common feature for all these systems. The new approach was tested by using a sample of sites (calibration sites) that provided NEE from flux tower observations and leaf area index data from satellite images (MODIS). For assessing the simulation accuracy, we applied the calibrated model to 42 additional sites (validation sites) across West Africa for which measured aboveground biomass data were available. The model showed a good performance regarding simulated biomass development. Overall, the comparison of simulated and observed biomass at sites with a dominating land cover of crops, grass or trees yielded correlation coefficients of 0.82, 0.94, and 0.77 and the Root Mean Square Error of 0.15, 0.22, and 0.12 kg m−2, respectively. In absolute terms, the model results indicate above-ground carbon stocks up to 1733, 3291, and 5377 kg C ha−1 yr−1 for agricultural, savanna grasslands, and savanna mixed tree-grassland sites. Carbon stocks as well as exchange rates correlated in particular with the abundance of trees. The simulations indicate higher grass biomass and crop yields under more humid climatic conditions as can be found in the Sudanian savanna region. Our study shows the capability of LandscapeDNDC to accurately simulate carbon balances in natural and agricultural ecosystems in semi-arid West Africa under a wide range of conditions, so that it might be used to assess the impact of land-use and climate change on the regional biomass productivity.

Jaber Rahimi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on gmd-2020-417', Juan Antonio Añel, 03 Mar 2021
    • AC1: 'Reply on CEC1', Rüdiger Grote, 05 Mar 2021
      • CEC2: 'Reply on AC1', Juan Antonio Añel, 05 Mar 2021
        • AC2: 'Reply on CEC2', Rüdiger Grote, 05 Mar 2021
  • RC1: 'Comment on gmd-2020-417', Zhipin Ai, 11 Mar 2021
    • AC3: 'Reply on RC1', Rüdiger Grote, 23 Apr 2021
  • RC2: 'Comment on gmd-2020-417', Anonymous Referee #2, 13 Mar 2021

Jaber Rahimi et al.

Jaber Rahimi et al.


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Short summary
West African Sahelian and Sudanian ecosystems are important regions for global carbon exchange and provide valuable food and fodder resources. Therefore, we simulate net ecosystem exchange and above-ground biomass of typical ecosystems in this region with an improved process-based bio-geochemical model, LandscapeDNDC. Carbon stocks as well as exchange rates correlated in particular with the abundance of trees. Grass and crop yields were increasing with humid climatic conditions.