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

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

Ceperley, Natalie C. (University of British Columbia; Swiss Federal Institute of Technology)
Mande, Theophile (Swiss Federal Institute of Technology)
van de Giesen, N.C. (TU Delft Water Resources)
Tyler, Scott (University of Nevada)
Yacouba, Hamma (International Institute for Water and Environmental Engineering (2iE))
Parlange, Marc B. (University of British Columbia; Swiss Federal Institute of Technology)

2017-08-22

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.

http://resolver.tudelft.nl/uuid:93b10ec4-2f74-4804-896d-98a449b1fecb

https://doi.org/10.5194/hess-21-4149-2017

1027-5606

Hydrology and Earth System Sciences, 21 (8), 4149-4167

Institutional Repository

journal article

© 2017 Natalie C. Ceperley, Theophile Mande, N.C. van de Giesen, Scott Tyler, Hamma Yacouba, Marc B. Parlange