Evaporation, sensible heal and canopy conductance of fallow savannah and patterned woodland in the Sahel

The behaviour of evaporation. sensible heat and canopy conductance of fallow savannah and patterned woodland in the Sahel is studied for the HAPEX-Sahel Intensive observation Period. Both fallow savannah and patterned woodland reach evaporation rates of 4-5 mm day(-1) during the rainy part of the IOP and show a decline, after the rains have ceased, to 2 mm day(-1). Sensible heat fluxes are different for the two vegetation types. This is also reflected in the behaviour of the evaporative fraction. analysis of the vegetation surface conductance of the vegetation part shows that maximum values for fallow savannah are around 10 mm s(-1), and for patterned woodland up to 40 mm s(-1). The response of the conductance to vapour pressure deficit is different for the two vegetation types. This is attributed to differences in C-3 and C-4 species composition. The consequences of these differences for modelling vegetation-atmosphere interaction in the semi-arid tropics are discussed.