Biophysical controls on evapotranspiration and water use efficiency in natural, semi-natural and managed African ecosystems

Christian Brümmer (1) , Lutz Merbold (2) , Sally Archibald (3) , Jonas Ardo (4) , Almut Arneth (5) , Nicolas Brüggemann (6) , Agnès de Grandcourt (7) , Laurent Kergoat (8) , Antje M. Moffat (9) , Éric Mougin (8) , Yann Nouvellon (10) , Laurent Saint-André (11) , Matthew Saunders (12) , Robert Scholes (3) , Elmar Veenendaal (13) , Werner Kutsch (1)

1 Institute of Agricultural Climate Research
2 Institute of Agricultural Sciences
3 Natural Resources and Environment
4 Department of Physical Geography and Ecosystem Science [Lund]
5 IMK-IFU - Institut für Meteorologie und Klimaforschung - Atmosphärische Umweltforschung
6 FZJ - Forschungszentrum Jülich GmbH | Centre de recherche de Jülich | Jülich Research Centre
7 Laboratory of Forest Ecology, Department of Forest Environment and Resource
8 GET - Géosciences Environnement Toulouse
9 MPI-BGC - Max Planck Institute for Biogeochemistry
10 UMR Eco&Sols - Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes
11 BEF - Unité de recherche Biogéochimie des Ecosystèmes Forestiers
12 SBES - School of Biology and Environmental Sciences
13 Nature Conservation and Plant Ecology Group

The effects of climatic factors and vegetation type on evapotranspiration (E) and water use efficiency (WUE) were analyzed using tower-based eddy-covariance (EC) data of eleven African sites (22 site years) located across a continental-scale transect. The seasonal pattern of E was closely linked to growing-season length and rainfall distribution. Although annual precipitation (P) was highly variable among sites (290 to 1650 mm), minimum annual E was not less than 250 mm and reached a maximum of 900 mm where annual P exceeded 1200 mm. Site-specific interannual variability in E could be explained by either changes in total P or variations in solar irradiance. At some sites, a highly positive linear correlation was found between monthly sums of E and net radiation (Rn), whereas a hysteretic relationship at other sites indicated that E lagged behind the typical seasonal progression of Rn. Results of a cross-correlation analysis between daily (24-h) E and Rn revealed that site-specific lag times were between 0 days and up to a few weeks depending on the lag of vapor pressure deficit (D) behind Rn and vegetation type. Physiological parameters (e.g. mean dry-foliage Priestley-Taylor alpha) implied that stomatal limitation to transpiration prevailed. During the rainy season, a strong linear correlation between monthly mean values of gross primary production (GPP) and E resulted in water use efficiency being constant with lower values at grass-dominated sites (~2 to ~3.5 g C kg-1 H2O) than at natural woodland sites and plantations (~4.5 to ~6 g C kg-1 H2O).

Domaines: Biodiversité et Ecologie

Christian Brümmer, Lutz Merbold, Sally Archibald, Jonas Ardo, Almut Arneth, et al.. Biophysical controls on evapotranspiration and water use efficiency in natural, semi-natural and managed African ecosystems. European Geosciences Union (EGU) General Assembly 2013, Copernicus Meetings. DEU., Apr 2013, Vienne, Austria. ⟨hal-01269350⟩