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Volume 21, issue 8 | Copyright

Special issue: Observations and modeling of land surface water and energy...

Hydrol. Earth Syst. Sci., 21, 4149-4167, 2017
https://doi.org/10.5194/hess-21-4149-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Aug 2017

Research article | 22 Aug 2017

Evaporation from cultivated and semi-wild Sudanian Savanna in west Africa

Natalie C. Ceperley1,2, Theophile Mande2, Nick van de Giesen3, Scott Tyler4, Hamma Yacouba5, and Marc B. Parlange1,2 Natalie C. Ceperley et al.
  • 1Department of Civil Engineering, Faculty of Applied Sciences, University of British Columbia, Vancouver, British Columbia, Canada
  • 2Laboratory of Environmental Fluid Mechanics and Hydrology, School of Architecture, Civil and Environmental Engineering, Swiss Federal Institute of Technology, Lausanne, Switzerland
  • 3Department of Civil Engineering and Geosciences, Delft University of Technology, Delft, the Netherlands
  • 4Department of Geological Sciences & Engineering, University of Nevada, Reno, NV, USA
  • 5Laboratory Hydrology and Resources in Water, International Institute for Water and Environmental Engineering (2iE), Ouagadougou, Burkina Faso

Abstract. Rain-fed farming is the primary livelihood of semi-arid west Africa. Changes in land cover have the potential to affect precipitation, the critical resource for production. Turbulent flux measurements from two eddy-covariance towers and additional observations from a dense network of small, wireless meteorological stations combine to relate land cover (savanna forest and agriculture) to evaporation in a small (3.5km2) catchment in Burkina Faso, west Africa. We observe larger sensible and latent heat fluxes over the savanna forest in the headwater area relative to the agricultural section of the watershed all year. Higher fluxes above the savanna forest are attributed to the greater number of exposed rocks and trees and the higher productivity of the forest compared to rain-fed, hand-farmed agricultural fields. Vegetation cover and soil moisture are found to be primary controls of the evaporative fraction. Satellite-derived vegetation index (NDVI) and soil moisture are determined to be good predictors of evaporative fraction, as indicators of the physical basis of evaporation. Our measurements provide an estimator that can be used to derive evaporative fraction when only NDVI is available. Such large-scale estimates of evaporative fraction from remotely sensed data are valuable where ground-based measurements are lacking, which is the case across the African continent and many other semi-arid areas. Evaporative fraction estimates can be combined, for example, with sensible heat from measurements of temperature variance, to provide an estimate of evaporation when only minimal meteorological measurements are available in remote regions of the world. These findings reinforce local cultural beliefs of the importance of forest fragments for climate regulation and may provide support to local decision makers and rural farmers in the maintenance of the forest areas.

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We relate land cover (savanna forest and agriculture) to evaporation in Burkina Faso, west Africa. We observe more evaporation and temperature movement over the savanna forest in the headwater area relative to the agricultural section of the watershed. We find that the fraction of available energy converted to evaporation relates to vegetation cover and soil moisture. From the results, evaporation can be calculated where ground-based measurements are lacking, frequently the case across Africa.
We relate land cover (savanna forest and agriculture) to evaporation in Burkina Faso, west...
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