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 N17-04-2008, European Geophysical Union, Vienna

Land surface fluxes and energy budget in the Saheland 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 0and identify the factors controlling these fluxes.Rnet = H + LE + G If you install a flux tower at 15 NYou have 60 % chance to get this24h averaged HLand surface fluxes and energy budget in the Sahel

You have 35 % chance to get this24h averaged HLand surface fluxes and energy budget in the Sahel

You have 5 % chance to get this24h averaged HLarge spatial variability !Land surface fluxes and energy budget in the Sahel

60 kmThe Hombori supersite : 3 main landscape units

rocky soilhigh run-offloamy-clayed soil lowland, ponds,high run-onsandy soilno run-off60 kmsoil type and water regime

Agoufou, sandy soil, grassland, no run-off run-onJune 06July 17August 19

Eguerit, rocky soil (gravel), no vegetation, high run-off

Kelma, loamy-clayed soil, open forest, high run-on

Timouk, Kergoat et al, subm.

Daily evapotranspiration and Fco2Agoufou ; High ETR, > 85% P rapidely returned to the atmosphere, High Fco2 (reaches 18mmol m-2s-1 at 12h)

Kelma : Extremely high ETR (>> P), Very high Fco2 (reaches 30mmol m-2s-1 at 12h)

Simple scaling of sensible heat flux to supersite scale (60 km)H = S wi. HiAveraged H close to Agoufou

ConclusionsHigh 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)

Thank you