The impact of rain events on CO2 emissions from contrasting land use systems in semi-arid West African savannas

Sina Berger; Jan Bliefernicht; Anja Linstädter; Kristijan Canak; Samuel Guug; Dominikus Heinzeller; Luitpold Hingerl; Matthias Mauder; Frank Neidl; Emmanuel Quansah; Seyni Salack; Rainer Steinbrecher; Harald Kunstmann

doi:10.1016/j.scitotenv.2018.07.397

The impact of rain events on CO₂ emissions from contrasting land use systems in semi-arid West African savannas

Sci Total Environ. 2019 Jan 10:647:1478-1489. doi: 10.1016/j.scitotenv.2018.07.397. Epub 2018 Jul 31.

Authors

Affiliations

¹ Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus Alpin, Garmisch-Partenkirchen, Germany; Institute of Geography, University of Augsburg, Augsburg, Germany. Electronic address: sina.berger@kit.edu.
² Institute of Geography, University of Augsburg, Augsburg, Germany.
³ Range Ecology and Range Management Group, Botanical Institute, University of Cologne, Germany; Institute of Crop Science and Resource Conservation, University of Bonn, Germany.
⁴ Range Ecology and Range Management Group, Botanical Institute, University of Cologne, Germany; Department of Geography, University of Bonn, Germany.
⁵ West African Science Service Centre on Climate Change and Adapted Land Use, WASCAL Competence Centre, Burkina Faso, Bolgatanga-Vea Watershed, Ghana.
⁶ Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus Alpin, Garmisch-Partenkirchen, Germany; Institute of Geography, University of Augsburg, Augsburg, Germany; University of Colorado Boulder, Cooperative Institute for Research in Environmental Sciences, NOAA/OAR/ESRL/Global Systems Division, Boulder, CO, USA.
⁷ Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus Alpin, Garmisch-Partenkirchen, Germany.
⁸ Department of Physics, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
⁹ West African Science Service Centre on Climate Change and Adapted Land Use, WASCAL Competence Centre, Burkina Faso.
¹⁰ Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus Alpin, Garmisch-Partenkirchen, Germany; Institute of Geography, University of Augsburg, Augsburg, Germany.

PMID: 30180353
DOI: 10.1016/j.scitotenv.2018.07.397

Abstract

In the future the Sudanian savanna - one of West Africa's high-potential "bread baskets" - will likely face shorter rainy seasons with more extreme rains and droughts. That could have serious impacts on the vegetation and its carbon dioxide (CO₂) exchange with potentially increasing CO₂ emissions accelerating climate warming. Understanding how the CO₂ fluxes in this area respond to environmental variables, in particular rain events, is essential, but available data are scarce. In this study, we monitored net ecosystem exchange (NEE) of CO₂, rainfall and other environmental parameters during four years at three savannas. Savannas were characterized by different vegetation due to different land use: i) woody and nearly pristine, ii) mixture of cropland and grassland and iii) intensive grazing. The impact of rain events on CO₂ exchange for these contrasting ecosystems were analyzed for single rain events (short-term) and on a yearly time scale (long-term) using three eddy covariance towers. We found that the woody pristine savanna site was a prominent sink of CO₂ (-864 to -1299 g CO₂ m^-2 y^-1) while the degraded sites were net CO₂ sources (118 to 605 g CO₂ m^-2 y^-1) with a complicated relation with annual rainfall amounts. The NEE responses to single rain events revealed that daytime rain systematically decreased the sink strengths at all sites, which might be associated with decreased light availability. At the degraded sites, additional factors increasing CO₂ losses were rain duration and dry spell length. The observed patterns of immediate CO₂ flux responses to rainfall at differently used savannas indicate strong internal feedbacks between vegetation and land use changes and raise the question whether the CO₂ sink strengths might be overestimated with possible implications for global CO₂ budgets. Sustainable adaptation strategies need to be developed for West Africa.

Keywords: Cropland; Dry spells; Grazing; Net ecosystem exchange of CO(2); Precipitation; Sudan savanna.