Trials

BACKGROUND: The aim of this open-label, randomized controlled trial conducted in four African countries (Madagascar, Niger, Central African Republic, and Senegal) is to compare three strategies of renutrition for moderate acute malnutrition (MAM) in children based on modulation of the gut microbiota with enriched flours alone, enriched flours with prebiotics or enriched flours coupled with antibiotic treatment. METHODS: To be included, children aged between 6 months and 2 years are preselected based on mid-upper-arm circumference (MUAC) and are included based on a weight-for-height Z-score (WHZ) between - 3 and - 2 standard deviations (SD). As per current protocols, children receive renutrition treatment for 12 weeks and are assessed weekly to determine improvement. The primary endpoint is recovery, defined by a WHZ >/= - 1.5 SD after 12 weeks of treatment. Data collected include clinical and socioeconomic characteristics, side effects, compliance and tolerance to interventions. Metagenomic analysis of gut microbiota is conducted at inclusion, 3 months, and 6 months. The cognitive development of children is evaluated in Senegal using only the Developmental Milestones Checklist II (DMC II) questionnaire at inclusion and at 3, 6, and 9 months. The data will be correlated with renutrition efficacy and metagenomic data. DISCUSSION: This study will provide new insights for the treatment of MAM, as well as original data on the modulation of gut microbiota during the renutrition process to support (or not) the microbiota hypothesis of malnutrition. TRIAL REGISTRATION: ClinicalTrials.gov, ID: NCT03474276 Last update 28 May 2018

Forcing a land surface model with satellite-derived biophysical products in the Sahel: Inpacts of various sources on the simulated energy and water cycles.

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Problématique de modélisation écohydrologique en région méditerranéenne karstique

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Estimation de l'évapotranspiration par télédétection spatiale : Enjeux et application en Afrique sahélienne

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Actions des surfaces sur l'atmosphère et sur les ressources hydriques et végétales: quelles évolutions au Sahel agro-pastoral ?

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Modélisation physique du cycle couplé de l'eau et de l'énergie en conditions tropicales sèches : une expérimentation à l'échelle locale dans le Sahel cultivé (Sud ouest du Niger)

International audienceIn the dry tropics in general and, particularly in the African Sahel, agro-ecosystems and hydrosystems are very sensitive to climate variability and land management. In turn, it has been shown that soil moisture, vegetation and surface fluxes produce substantial feedback effects on rainfall-producing atmospheric convection. Therefore, it is of prime importance to understand and to model the dynamics of the soil-plant-atmosphere continuum in response to contrasted meteorological and terrestrial conditions for this area. The objective of this study is to produce a process-based model of water and energy transfers in the soil and land-atmosphere interface over an entire 5-year period, at local scale, for the two main land cover types of South-West Niger: millet-crop and fallow savannah. A comprehensive dataset is available over that whole period in two such fields of the Wankama catchment, making it a rather unique asset for West Africa. This area is typical of the central Sahel conditions, with 400-600 mm annual rainfall concentrated in the 4-5 months wet season, followed by the 7-8 months dry season. Soils are essentially sandy and prone to surface crusting, which induces a strong vertical contrast in hydrodynamic properties. The dataset used here includes 5 years of atmospheric forcing (rainfall, wind speed, sun and atmosphere radiation, air temperature and moisture) and validation variables (net radiation, turbulent fluxes and soil temperature and moisture profiles), recorded every 30 min. The seasonal course of vegetation phenology (LAI, height, biomass) and soil characteristics (particle size and density profiles) are also available. The SiSPAT (Simple Soil-Plant-Atmosphere Transfer, Braud et al., 1995) physically-based model is used for this study. It solves the mass and heat transfer system of equations in the soil, with vapour phase, coupled with a two-component (bare soil and one vegetation layer) water and energy budget at the surface-atmosphere interface. Main questions raised in this modeling exercise were, whether such a model could be adequately calibrated and validated for the two studied sites, using realistic parameter values and, what uncertainty would result for model outputs (surface fluxes and soil heat/water profiles). The model was calibrated over a 2-year period and then validated over the other three years, for both sites. In both cases, observations are reproduced about as well for the two periods. The variations in water and energy variables, over the five contrasting years and between land covers, are highlighted. Multi-year, field-based estimations of land surface water and energy budgets are hence produced, for the first time in this area to our knowledge. Given model performances, it is felt that it can be applied with reasonable confidence to much longer periods, reflecting the strong variability that characterizes the Sahel climate. This modeling experiment takes part in the ALMIP (AMMA Land Model Intercomparison) project, which aims at comparing land surface models at local and meso scales over a north-south eco-climate gradient represented by three West-African sites of the AMMA-CATCH observatory (RBV network)

Construction d'une climatologie fondés sur l'observation et la modélisation des bilans hydriques et énergétiques de deux types de cultures dominantes dans le Sahel cultivé. Bilans annuels et saisonnalité

International audienceIn the sub-Saharan Sahel, energy and water cyclingat the land surface is pivotal for the regional climate,water resources and land productivity, yet it is still verypoorly documented. As a step towards a comprehensive climatological description of surface fluxes in this area, thisstudy provides estimates of long-term average annual budgetsand seasonal cycles for two main land use types of thecultivated Sahelian belt: rainfed millet crop and fallow bush.These estimates build on the combination of a 7-year fielddata set from two typical plots in southwestern Niger withdetailed physically based soil-plant-atmosphere modeling,yielding a continuous, comprehensive set of water and energyflux and storage variables over this multiyear period. Inthe present case in particular, blending field data with mechanistic modeling makes the best use of available data andknowledge for the construction of the multivariate time series.Rather than using the model only to gap-fill observationsinto a composite series, model-data integration is generalizedhomogeneously over time by generating the wholeseries with the entire data-constrained model simulation. Climatological averages of all water and energy variables, withassociated sampling uncertainty, are derived at annual to subseasonal scales from the time series produced. Similaritiesand differences in the two ecosystem behaviors are highlighted.Mean annual evapotranspiration is found to represent82-85% of rainfall for both systems, but with differentsoil evaporation/plant transpiration partitioning and differentseasonal distribution. The remainder consists entirelyof runoff for the fallow, whereas drainage and runoff standin a 40-60% proportion for the millet field. These resultsshould provide a robust reference for the surface energy- andwater-related studies needed in this region. Their significanceand the benefits they gain from the innovative data-modelintegration approach are thoroughly discussed. The modeldeveloped in this context has the potential for reliable simulations outside the reported conditions, including changingclimate and land cover

Modélisation de l'effet de la variabilité inter-annuelle des conditions météorologiques et des conditions de surface sur les transferts couplés d'eau et de chaleur dans le Sahel cultivé

International audienceIn the dry tropics in general and in the African Sahel in particular, hydro-ecosystems are very sensitive to climate variability and land management. In the Niamey region of South-West Niger, a severe multi-decadal drought together with large-scale vegetation clearing coincided with an unexpected increase in surface and ground water resources. Such an apparent paradoxical situation illustrates the complex way in which climate and land cover interactions control the Sahelian water cycle dynamics. This stresses the importance of understanding and reliably modeling water/energy transfers in the local soil-plant-atmosphere system, under contrasted meteorological and surface conditions. This study investigates the effects of the inter-annual variability of meteorological and land use conditions on the coupled water and energy cycles in the cultivated Sahel over a 5-year period. This is based on a comprehensive multi-year field dataset acquired for a millet crop field and a fallow savannah, the two main land cover types of South-West Niger (Wankama catchment in the mesoscale AMMA-CATCH Niger observatory, part of the French-initiated RBV network). It includes atmospheric forcing, seasonal course of vegetation phenology, soil properties and model validation variables (net radiation, turbulent fluxes, soil heat/water profiles), for the two fields. The study area is typical of Central Sahel conditions, with 400-600 mm annual rainfall concentrated in the 4-5 month wet season. Soils are mainly sandy and prone to surface crusting, leading to a strong vertical contrast in hydrodynamic properties. The SiSPAT process-based model used solves the 1D mass and heat transfer system of equations in the soil, including vapor phase and coupled with a two-component (bare soil and vegetation) water and energy budget at the surface-atmosphere interface. The study explores whether such a model can be accurately calibrated and validated for the two sites using realistic-parameter values. The model is calibrated over a 2-year period and validated over the other three remaining years for the two sites. The variations in water and energy variables over the five contrasted years and between land covers are highlighted. Multi-year, field-based estimations of land surface water and energy budgets are produced, for the first time in this Sahelian region to our knowledge. Given model skills, the model can be applied reliably to much longer periods, reflecting the strong variability that characterizes the Sahel climate

Modélisation à l'échelle locale des processus de surface dans le Sahel cultivé (AMMA-CATCH Noger)

International audienceIn the African Sahel, agro-hydro-ecosystems are very sensitive to climate variability and land management. In turn, soil moisture, vegetation and surface fluxes provide substantial feedback on atmospheric convection and rainfall generation. It is very important to understand and correctly model the dynamics of the soil-plant-atmosphere continuum in this region, in response to contrasted meteorological and surface conditions. The aim of this study is to generate a local-scale process-based model of water and energy transfers at the soil-land-atmosphere interface for millet crop and fallow savannah, the two main land cover types in the cultivated Sahel. This study is based on a comprehensive 5-year dataset (2005-2009) from the Wankama catchment of the AMMA-CATCH observatory in south-west Niger. It includes atmospheric forcing, seasonal course of vegetation phenology, soil properties and model validation variables (net radiation, turbulent fluxes, soil heat/water profiles), for the two fields. The study area is typical of the central Sahel conditions, with 400-600 mm annual rainfall concentrated in the 4-5 month wet season. Soils are mainly sandy and prone to surface crusting, leading to a strong vertical contrast in hydrodynamic properties. The SiSPAT physically-based model is used for this study. It solves the mass and heat transfer system of equations in the soil with a vapor phase, coupled with a two-component (bare soil and vegetation) water and energy budget at the surface-atmosphere interface. The study investigates whether such a model can be accurately calibrated and validated for the two sites using realistic-parameter values. The model is calibrated over a 2-year period (2005-2006) and validated over the other three years for the two sites. The variations in water and energy variables over the five contrasted years and between land covers will be highlighted. Multi-year, field-based estimations of land surface water and energy budgets will be produced. The model could eventually be applied to longer periods to account for the marked variability of the Sahel climate. This modeling study is part of the ALMIP-2 (AMMA Land Model Intercomparison – Phase 2) project, for evaluation and comparison of land surface models at local and meso scales over the AMMA-CATCH north-south eco-climate gradient of West Africa