L. Kergoat, F. Timouk, E. Mougin, E. Ceschia, P. Hiernaux, P. de Rosnay, V. Le Dantec CESBIO, Toulouse, France C.R. Lloyd , C.M. Taylor, CEH, Wallingford UK. Response of sensible, latent and CO2 fluxes ateral water redistribution and vegetation developm in a Sahelian landscape at 15 °N -04-2008, European Geophysical Union, Vienna
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L. Kergoat, F. Timouk, E. Mougin, E. Ceschia, P. Hiernaux, P. de Rosnay, V. Le Dantec CESBIO, Toulouse, France C.R. Lloyd, C.M. Taylor, CEH, Wallingford.
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L. Kergoat, F. Timouk, E. Mougin, E. Ceschia,P. Hiernaux, P. de Rosnay, V. Le DantecCESBIO, Toulouse, France
C.R. Lloyd , C.M. Taylor,CEH, Wallingford UK.
Response of sensible, latent and CO2 fluxes to lateral water redistribution and vegetation development
in a Sahelian landscape at 15 °N
17-04-2008, European Geophysical Union, Vienna
Land surface fluxes and energy budget in the Sahel
A lot has been said ...
from the Otterman, Charney, Jackson, Idso, Ripley debate in 1975on albedo and (over) grazing and the Sahel drought
....
to Notaro et al. 2008 Global Change Biology negative feedback : rainfall / land surface / rainfallassuming bare soil evaporates more than grasses (!)
Almost nothing has been measured !
except SEBEX (near Niamey, 13.5 °N, 1990, 1991) HAPEX-Sahel (near Niamey, 1992) bush fallow, millet, tiger bush
and nothing at all in central and northern Sahel.
Lat 15° N, Lon 0° : the most studied grid point in the Sahel... by modelers only, sofar ....
Objectives : to present SEB and turbulent fluxes at lat 15° N, lon 0°and identify the factors controlling these fluxes.Rnet = H + LE + G
If you install a flux tower at 15° NYou have 60 % chance to get this
24h averaged H
Land surface fluxes and energy budget in the Sahel
You have 35 % chance to get this
24h averaged H
Land surface fluxes and energy budget in the Sahel
You have 5 % chance to get this
24h averaged H
Large spatial variability !
Land surface fluxes and energy budget in the Sahel
60 km
The Hombori supersite : 3 main landscape units
rocky soilhigh run-off
loamy-clayed soil lowland, ponds,high run-on
sandy soilno run-off
60 km
soil type and water regime
Agoufou, sandy soil, grassland, no run-off run-on
June 06
July 17
August 19
Eguerit, rocky soil (gravel), no vegetation, high run-off
Kelma, loamy-clayed soil, open forest, high run-on
H = Rnet
H < 0
high LE
H Rnet
Timouk, Kergoat et al, subm.
Daily evapotranspiration and Fco2
Agoufou ; High ETR, > 85% P rapidely returned to the atmosphere, High Fco2 (reaches 18mol m-2s-1 at 12h)
Kelma : Extremely high ETR (>> P), Very high Fco2 (reaches 30mol m-2s-1 at 12h)
Simple scaling of sensible heat flux to supersite scale (60 km)H = wi. Hi
Averaged H close to Agoufou
Conclusions
High spatial variability of surface fluxes (including some very high ETR and Fco2 !)
Lateral water redistribution and soil type controls :
- soil moisture in the root zone- vegetation growth & vegetation type- Rnet- flux partitionning
Landscape units large enough to maintain CBL gradients (mesoscale circulation?)
Simple scaling shows that 60 km x 60 km average is close to Agoufou site
Preliminary comparison implies ECMWF H flux is too high, more to come (ALMIP)