Actual evapotranspiration and canopy resistance measurement of the savannah in the Kouilou basin (Congo-Brazzaville).

The aim of this work is to study the actual evapotranspiration and surface resistance of the savannah using the Bowen-ratio method for two contrasted periods, dry and rainy season. The reliability of this method has been assessed by comparison with the Monteith equation and the soil-water balance method in a 90% Loudetia arundinacea dominated savannah (Pointe Noire, Congo). Our results relate to the period from 18 September to 11 October 1998 (24 days): (a) from 18 to 29 September ('dry season'), the soil-water content was less than 70% of the soil-water content at field capacity (63-70% of R; large soil-water stress; T/ E from 0.2 to 0.4); (b) from 30 September to 11 October ('rainy season') soil-water content close to 90-92% of RFC; no soil-water stress; T/ E from 0.73 to 0.77). The mean daily surface resistance reulting from the Bowen-ratio method was 317 s m, 355 s m during the 'dry season' and 279 s m during the 'rainy season'. The total actual evapotranspiration ( E) resulting from the Bowen-ratio method, Penman-Monteith equation and soil-water balance method were, respectively of 58.6-57.8 and 56.2 mm, with the mean daily E of 2.4-2.4 and 2.3 mm day (2.4-1.5 and 2.2 mm day in 'dry season' and of 2.5-3.4 and 2.5 mm day in 'rainy season'). The Bowen-ratio method was used for the assessment of the actual evapotranspiration from the temperature and specific humidity differences, net radiation and the soil heat flux measurement: its advantages are a rapidity of installation, a temporal resolution of measurement in less than one hour and a good integration of the heterogeneousness of the savannah's latent flux of vaporization. This method is adapted to eco-physiological studies in tropical conditions with reduced teams. [ABSTRACT FROM AUTHOR]