Effect of seasonal dynamics of vegetation cover on land surface models: a case study of NOAH LSM over a savanna farm land in eastern Burkina Faso, West Africa

International audienceThe sensitivity of the land surface model of the National Centers for Environmental Prediction (NCEP), the Oregon State University, the Air Force and the Hydrologic Research Lab (NOAH LSM) was evaluated with respect to the seasonal dynamics of the vegetation cover in the savanna area under intensive agriculture in the eastern part of Burkina Faso, West Africa. The data collected during the first long-term measurement of the surface fluxes in this mentioned region was used for this purpose. The choice of NOAH LSM was motivated by the fact that it has already been tested in different environments in West Africa, especially in Ghana. The sensitivity was tested by comparing the simulated surfaces fluxes using a fixed values of the roughness length for momentum as a standard in the model and the true seasonal value of this variable. The results show that NOAH LSM was not sensitive to the change of the roughness length for momentum neither on a seasonal basis nor on a daily basis, which was found to be abnormal. The formulation of the coefficient (Bc) coupling the dry canopy transpiration to the atmosphere was found to be the main reason for this. An improved formulation for this coefficient was given to solve this insensitivity and to improve the performance of the model. Recommendations are also given to enhance the performance of the model in the West African savanna environment

Corrélation entre les flux de chaleur sensible et latente avec la longueur de rugosité de surface. Influence sur la disponibilité des ressources en eau sur les terres intensivement exploitées de l’Est du Burkina Faso.

 L’exploitation des terres, exprimée par la longueur de rugosité de surface zo, est un facteur important qui influence le processus d’échange d’énergie entre la surface de la terre et l’air. Cette étude qui s’intègre dans le cadre des travaux de thèse intitulés « Impact de l’exploitation des terres sur le bilan hydrologique dans les bassins versants de l’Est du Burkina Faso » met en relation les principaux termes du bilan d’énergie (le flux de chaleur sensible et latente) avec la longueur de rugosité de surface zo calculée à l’aide de la loi de similarité de Moninh - Obhukoh.  La méthodologie est basée sur l’observation des données micro-météorologiques qui sont constituées des mesures simultanées des moyennes sur chaque heure de la vitesse du vent, du flux de chaleur sensible et latente et la température. Ces mesures ont été effectuées à 10 m du sol qui constitue la hauteur du mat de la station installée à l’Est du Burkina Faso précisément à Tanyele (département de Kompienga). Un anémomètre sonique triaxial est utilisé pour la mesure du flux de chaleur sensible, de la vitesse du vent et la température de l’air. L’hygromètre Campbell KH2O à krypton est utilisé pour la mesure du flux de chaleur latente. Le traitement des données brutes a été effectué par corrélation de remous en temps réel (chaque heure) à l’aide du logiciel ALTEDDY.  Les résultats montrent qu’il y a une bonne corrélation entre la longueur de rugosité de surface et les principaux termes du bilan d’énergie sur l’ensemble des données. Pour les données collectées sur une année, nous pouvons noter que le flux de chaleur sensible décroît exponentiellement lorsque la longueur de rugosité de surface croit (R2=- 0.84). De même le flux de chaleur latente croit de façon logarithmique avec la longueur de rugosité de surface (R2= 0.79). Lorsque nous analysons les données séparément sur les deux principales saisons qui caractérisent la zone d’étude (saison sèche et saison pluvieuse), nous constatons que la longueur de rugosité de surface n’a pas un impact significatif sur le flux de chaleur sensible et latente. D’autres paramètres climatiques tels que la radiation solaire, l’humidité relative et la température de l’air les déterminent. Cependant en saison pluvieuse, la longueur de rugosité de surface influence très négativement le flux de chaleur sensible (R2= - 0.92) contrairement au flux de chaleur latente qui montre une décroissance qui n’est pas aussi significative (R2= - 0.49). Cette décroissance du flux de chaleur sensible avec la longueur de rugosité de surface en saison pluvieuse peut entraîner une bonne recharge de la nappe si les écoulements de surface ne sont pas assez importants. Nous aurons besoin de beaucoup plus de données pour avoir des informations fiables sur la tendance croissante du flux de chaleur latente avec la longueur de rugosité de surface observée sur l’ensemble des données collectées

Recommandations specifiques d'engrais: Calibration et validation du module phosphore du modele NuMaSS

Fertiliser recommendations in Mali as well as in many other countries of West Africa were made according to Chaminade's method. For socio-economic reasons, correcting deficiency rates of major nutrients were vulgarized. These blanket recommendation, when applied, lead to a continuous soil nutrient mining. The objective of this research was to calibrate and validate the P module of NuMass. Laboratory incubations were conducted to calibrate the P buffering coefficients used by the P module. Rates of N, P and lime predicted by NuMass model, considered as specific recommendations, were compared to the blanket recommendations in the field in order to validate them. The buffer coefficients were inversely proportional to the clay content. The buffering coefficient of sandy soils of Cinzana/Mali (0.73) and Kollo/Niger P3 (0.63) were higher compared to the clayey soils of Longorola-bf (0.22) and Kollo/Niger (0.21). Generally, buffering coefficients obtained by laboratory incubation (0.60) tended to be lower than the estimated coefficient by the P module NuMass (0.67). The range of the used soil texture (1.5-54.6 % clay) showed that the buffering coefficients estimated by the P module of NuMass were correct for flooded soils. Grain yield of different trials and tests do not indicate the expected higher performance of specific recommendations of fertilisers from NuMass model compared to the used blanket recommendation (1624 and 1582 kg ha-1 of maize; respectively

Spatial distribution of the chromosomal forms of anopheles gambiae in Mali

<p>Abstract</p> <p>Background</p> <p>Maps of the distribution of malaria vectors are useful tools for stratification of malaria risk and for selective vector control strategies. Although the distribution of members of the <it>Anopheles gambiae </it>complex is well documented in Africa, a continuous map of the spatial distribution of the chromosomal forms of <it>An. gambiae s.s. </it>is not yet available at country level to support control efforts.</p> <p>Methods</p> <p>Bayesian geostatistical methods were used to produce continuous maps of the spatial distribution of the chromosomal forms of <it>An. gambiae s.s</it>. (Mopti, Bamako, Savanna and their hybrids/recombinants) based on their relative frequencies in relation to climatic and environmental factors in Mali.</p> <p>Results</p> <p>The maps clearly show that each chromosomal form favours a particular defined eco-climatic zone. The Mopti form prefers the dryer northern Savanna and Sahel and the flooded/irrigated areas of the inner delta of the Niger River. The Savanna form favours the Sudan savanna areas, particularly the South and South-Eastern parts of the country (Kayes and Sikasso regions). The Bamako form has a strong preference for specific environmental conditions and it is confined to the Sudan savanna areas around urban Bamako and the Western part of Sikasso region. The hybrids/recombinants favour the Western part of the country (Kayes region) bordering the Republic of Guinea Conakry.</p> <p>Conclusion</p> <p>The maps provide valuable information for selective vector control in Mali (insecticide resistance management) and may serve as a decision support tool for the basis for future malaria control strategies including genetically manipulated mosquitoes.</p

Results analysis and validation - D5.3

This deliverable describes the validation processes followed to assess the performance of the algorithms and protocols for the operator governed opportunistic networking as defined in the OneFIT Project. Therefore, this document includes the description of the set-up of the different validation platforms, the design of the test plans for each one of them, and the analysis of the results obtained from the tests. A per-scenario approach rather than a per-platform approach has been followed, so an additional analysis has been performed, gathering the results related to each scenario, in order to validate the premises stated to each one of them. The OneFIT concept has been therefore validated for all foreseen business scenarios

Impact of land-use intensity on evaporation and surface runoff: Processes and parameters for Eastern Burkina Faso, West Africa

Land-use is one of the main factors affecting the hydrological cycle in the Volta river basin, where two major projects (GLOWA-Volta and VinVal) are dealing with the elaboration of a land-use planning and decision support system for sustainable agricultural production and water resource management. Both projects, especially GLOWA-Volta need information about the seasonal dynamics of the actual evaporation and surface runoff. Therefore, the inter-annual dynamics of the actual evaporation, effect of land-use on the evaporation and on land surface models were analyzed via surface flux measurements during the first long-term eddy covariance measurement over the savanna vegetation in West Africa. The investigation took place in eastern Burkina Faso; the analysis covers almost two years, including one relatively wet (2003) and one relatively dry (2004) year. Surface runoff and scale effect were also investigated in three adjacent watersheds with different land-use intensity during the 2004 rainy season.Civil Engineering and Geoscience

Energy balance closure and footprint analysis using Eddy Covariance measurements in Eastern Burkina Faso, West Africa

International audienceThe quality and the representativeness of the first long-term Eddy Covariance measurements in the savanna zone of West Africa were investigated using the energy balance closure and the footprint analysis. The quality and representativeness of the first long-term Eddy Covariance measurements over the West African savanna were investigated using the energy balance closure and the footprint analysis. The analysis covered four contrasting periods such as the complete dry season (January to March 2004), the dry to wet transition period (April to May 2004), the rainy season (June to September 2004) and the wet to dry transition period (October to November 2004). The results show that the overall energy balance closure can be considered as satisfactory over the whole dataset. The regression fit between (Rn?G) and (H+?E) was significant (Pr2) of 0.80 and a slope of 0.88, while the intercept was 25W/m2. The energy balance closure was affected by rain during the rainy season (r2=0.69), and by sampling problems during the transition periods (R2 were 0.80 and 0.86, respectively). The footprint analysis shows that the fetch ranged between 20 m (daytime) and 800 m (nighttime). This range showed that the fetch was adequate and fluxes sampled were representative, especially during the rainy season when the vegetal cover was dominated by crops and grasses with scale length of a few meters. During the dry season when the surface is free from crops and grasses, the measurements were also representative as about 60% of the trees around the station were contributing to the measured fluxes. However, during the transition periods some sampling problems appeared, less than 30% of the trees were contributing to the measured fluxes. The relevance of the dominant wind direction in the representativeness of the measurements was also discussed