Erosion éolienne dans les régions arides et semi-arides africaines : processus physiques, métrologie et techniques de lutte

Cette étude présente une approche par modélisation pour estimer les émissions de particules terrigènes provenant de la région semi-aride sahélienne. Deux modèles spécifiques ont été combinés : l'un pour représenter le couvert herbacé saisonnier au Sahel, l'autre pour quantifier les émissions de particules terrigènes. Le Sahel (12°N–20°N, 20°W–35°E) constitue la région d'étude et les simulations ont été effectuées à une résolution spatiale de 0,25° sur une période de 4 ans (2004-2007). Le forçage pluviométrique provient d'un produit satellitaire TRMM (Tropical Rainfall Measuring Mission). Les autres forçages météorologiques ont été fournis par le CEPMMT (Centre Européen pour les Prévisions Météorologiques à Moyen Terme). La rugosité aérodynamique de la surface a été estimée à partir d'une paramétrisation empirique pour représenter sa dynamique temporelle à partir des simulations du couvert végétal saisonnier. Les simulations de végétation ont été comparées à des observations satellitaires au préalable. Lorsqu'aucune végétation ne pousse, les propriétés de la surface ont été considérées constantes et déduites de mesures satellitaires. Les flux d'émission annuels simulés sont compris entre 100 et 400 Mt pour l'ensemble de la région considérée, en accord avec des travaux précédents portant sur le Sahara. Leur variabilité interannuelle est aussi en accord avec les observations satellitaires. Nous avons par ailleurs mis en évidence l'existence d’une "frange émissive saisonnièrement végétalisée" dont la superficie varie selon l'année et pour laquelle les émissions annuelles sont comprises entre 0,5 Mt et 20 Mt pour la période considérée. L'inhibition en masse de ces émissions due à la végétation saisonnière et à l'humidité superficielle du sol sur cette frange varie de 20% à 35%

Erosion éolienne dans les régions arides et semi-arides africaines : processus physiques, métrologie et techniques de lutte

Les régions arides du sud de la Tunisie sont des zones naturellement très sensibles à l'érosion éolienne. Non seulement les précipitations dans ces régions sont faibles (inférieures à 200 mm), mais les sols sont fins, sableux et peu profonds, c'est-à-dire facilement érodables par le vent. L'utilisation de nouvelles techniques agricoles à la place des techniques traditionnelles a conduit à une augmentation de l'érosion éolienne dans ces régions. Par exemple, l'augmentation croissante de l'utilisation de la déchaumeuse à disques a eu d'importantes conséquences sur la dégradation des champs en modifiant la structure des sols et les caractéristiques de leur surface. Le présent travail de modélisation est centré sur la quantification de la déflation éolienne à l'échelle du sud tunisien en vue de déterminer en particulier les zones les plus sensibles à ce phénomène pour des objectifs de diagnostic et de stratégie de lutte efficace contre l'érosion éolienne. Les flux d'érosion éolienne sur le sud de la Tunisie ont été simulés pour l'année 2008 à une résolution de 10 km x 10 km en prenant en compte le type d'usage des sols et les pratiques agricoles associées à l'aide du modèle d'érosion éolienne Dust Production Model (DPM, Marticorena et Bergametti [1995] ; Alfaro et al. [1998]). Afin de prendre en compte les différents types d'outils agricoles utilisés sur le domaine étudié, les paramétrisations du seuil et du flux d'érosion éolienne en fonction des caractéristiques des billons de labour (hauteur et espacement) développées par Kardous et al. [2005a ; b] ont été intégrées au DPM. [...

How surface properties influence mineral dust emissions in the Sahelian region ? A modelling case study during AMMA

Tropical mesoscale convective systems (MCSs) are a prominent feature of the African meteorology. A continuous monitoring of the aeolian activity in an experimental site located in Niger shows that such events are responsible for the major part of the annual local wind erosion, i.e. for most of the Sahelian dust emissions [Rajot, 2001]. However, the net effect of these MCSs on mineral dust budget has to be estimated: on the one hand, these systems produce extremely high surface wind velocities leading to intense dust uptake, but on the other hand, rainfalls associated with these systems can efficiently remove the emitted dust from the atmosphere. High resolution modelling appears as a relevant approach to correctly reproduce the surface meteorology associated with such meteorological systems [Bouet et al., submitted]. The question now arising concerns the reliability of surface characteristics available for the Sahelian region, especially soil texture and surface roughness, which are critical parameters for dust emissions. Contrary to arid regions, which are now well documented, data is still missing to correctly characterize semi-arid regions like the Sahel. This is in particular due to the well pronounced annual cycles of precipitations and vegetation in these regions and to the impact of land-use on surface properties. This study focuses on a case study of dust emission associated with the passage of a MCS observed during one of the Special Observing Periods of the international African Monsoon Multidisciplinary Analysis (AMMA – SOPs 1-2) program. The simulations were made using the Regional Atmospheric Modeling System (RAMS, Cotton et al. [2003]) coupled online with the dust production model developed by Marticorena and Bergametti [1995] and recently improved by Laurent et al. [2008] for Africa. The sensitivity of dust emission associated with the passage of the MCS to surface features is investigated using different data sets of surface properties (Harmonized World Soil Database, HWSD) and land-use (GLOBCOVER). In-situ measurements of dust concentrations (both ground-based and airborne), and of dust emission flux are used to validate the simulations

The blood acid base and gastrointestinal response to three different forms of sodium citrate encapsulation

Enterically coated (ENT) or delayed-release (DEL) capsules may lessen gastrointestinal symptoms (GIS) following acute sodium citrate (SC) ingestion, although the effects on blood acid-base balance are undetermined. Fourteen active males ingested 0.4  g.kg−1 body mass (BM) SC, within gelatine (GEL), DEL and ENT capsules or 0.07 g.kg−1 BM sodium chloride control (CON). Blood acid-base balance and GIS were measured for 4 h. Ingestion form had no significant effect on total GIS experienced (GEL: 2 ± 7; DEL: 1  ± 8; ENT: 1 ± 4 AU). Most (7/14) participants experienced zero symp-toms throughout. Peak GIS typically emerged ≤100 min post- ingestion, with a similar time to reach peak GIS between ingestion form (GEL: 36 ± 70; DEL: 13 ± 28; ENT: 15 ± 33 AU). Blood [HCO3−] was significantly higher with ENT versus GEL (ENT: 29.0 ± 0.8; GEL: 28.5 ± 1.1 mmol.L−1, P = 0.037). Acute ingestion of a reduced SC dose elicited minimal GIS, producing significant changes in blood [HCO3−] from rest, irrespective of ingestion form (GEL: 6.0 ± 0.9; DEL: 5.1 ± 1.0; ENT: 6.2 ± 0.8 mmol.L−1). The necessity of individualized ingestion strategies is also challenged, with sustained increases in blood [HCO3−] of ≥4 mmol.L−1 for up to 153 min highlighted. If commencing exercise at peak alkalosis augments subsequent per-formance above starting at a standardized time point where HCO3− is still elevated remains unclear

Variability of aerosol vertical distribution in the Sahel

In this work, we have studied the seasonal and inter-annual variability of the aerosol vertical distribution over Sahelian Africa for the years 2006, 2007 and 2008, characterizing the different kind of aerosols present in the atmosphere in terms of their optical properties observed by ground-based and satellite instruments, and their sources searched for by using trajectory analysis. This study combines data acquired by three ground-based micro lidar systems located in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analysis (AMMA), by the AEROsol RObotic NETwork (AERONET) sun-photometers and by the space-based Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the CALIPSO satellite (Cloud-Aerosol Lidar and Infrared Pathfinder Observations). <br><br> During winter, the lower levels air masses arriving in the Sahelian region come mainly from North, North-West and from the Atlantic area, while in the upper troposphere air flow generally originates from West Africa, crossing a region characterized by the presence of large biomass burning sources. The sites of Cinzana, Banizoumbou and M'Bour, along a transect of aerosol transport from East to West, are in fact under the influence of tropical biomass burning aerosol emission during the dry season, as revealed by the seasonal pattern of the aerosol optical properties, and by back-trajectory studies. <br><br> Aerosol produced by biomass burning are observed mainly during the dry season and are confined in the upper layers of the atmosphere. This is particularly evident for 2006, which was characterized by a large presence of biomass burning aerosols in all the three sites. <br><br> Biomass burning aerosol is also observed during spring when air masses originating from North and East Africa pass over sparse biomass burning sources, and during summer when biomass burning aerosol is transported from the southern part of the continent by the monsoon flow. <br><br> During summer months, the entire Sahelian region is under the influence of Saharan dust aerosols: the air masses in low levels arrive from West Africa crossing the Sahara desert or from the Southern Hemisphere crossing the Guinea Gulf while in the upper layers air masses still originate from North, North-East. The maximum of the desert dust activity is observed in this period which is characterized by large AOD (above 0.2) and backscattering values. It also corresponds to a maximum in the extension of the aerosol vertical distribution (up to 6 km of altitude). In correspondence, a progressive cleaning up of the lowermost layers of the atmosphere is occurring, especially evident in the Banizoumbou and Cinzana sites. <br><br> Summer is in fact characterized by extensive and fast convective phenomena. <br><br> Lidar profiles show at times large dust events loading the atmosphere with aerosol from the ground up to 6 km of altitude. These events are characterized by large total attenuated backscattering values, and alternate with very clear profiles, sometimes separated by only a few hours, indicative of fast removal processes occurring, likely due to intense convective and rain activity. <br><br> The inter-annual variability in the three year monitoring period is not very significant. An analysis of the aerosol transport pathways, aiming at detecting the main source regions, revealed that air originated from the Saharan desert is present all year long and it is observed in the lower levels of the atmosphere at the beginning and at the end of the year. In the central part of the year it extends upward and the lower levels are less affected by air masses from Saharan desert when the monsoon flow carries air from the Guinea Gulf and the Southern Hemisphere inland

Temporal variability of mineral dust in southern Tunisia : analysis of 2 years of PM10 concentration, aerosol optical depth, and meteorology monitoring

International audienceThe south of Tunisia is a region very prone to wind erosion. During the last decades, changes in soil management have led to an increase in wind erosion. In February 2013, a ground-based station dedicated to the monitoring of mineral dust (that can be seen in this region as a proxy of the erosion of soils by wind) was installed at the Institut des Régions Arides (IRA) of Médenine (Tunisia) to document the temporal variability of mineral dust concentrations. This station allows continuous measurements of surface PM10 concentration (TEOM™), aerosol optical depth (CIMEL sunphotometer), and total atmospheric deposition of insoluble dust (CARAGA automatic sampler). The simultaneous monitoring of meteorological parameters (wind speed and direction, relative humidity, air temperature, atmospheric pressure, and precipitations) allows to analyse the factors controlling the variations of mineral dust concentration from the sub-daily to the annual scale. The results from the two first years of measurements of PM10 concentration are presented and discussed. In average on year 2014, PM10 concentration is 56 µg/m3. However, mineral dust concentration highly varies throughout the year: very high PM10 concentrations (up to 1,000 µg/m3 in daily mean) are frequently observed during wintertime and springtime, hardly ever in summer. These episodes of high PM10 concentration (when daily average PM10 concentration is higher than 240 µg/m3) sometimes last several days. By combining local meteorological data, air-masses trajectories, sunphotometer measurements, and satellite imagery, the part of the high PM10 concentration due to local emissions and those linked to an advection of dusty air masses by medium and long range transport from the Sahara desert is quantified

The MACC-II 2007–2008 reanalysis: atmospheric dust evaluation and characterization over northern Africa and the Middle East

In the present work, atmospheric mineral dust from a MACC-II short reanalysis run for 2 years (2007–2008) has been evaluated over northern Africa and the Middle East using satellite aerosol products (from MISR, MODIS and OMI satellite sensors), ground-based AERONET data, in situ PM10 concentrations from AMMA, and extinction vertical profiles from two ground-based lidars and CALIOP satellite-based lidar. The MACC-II aerosol optical depth (AOD) spatial and temporal (seasonal and interannual) variability shows good agreement with those provided by satellite sensors. The capability of the model to reproduce the AOD, Ångström exponent (AE) and dust optical depth (DOD) from daily to seasonal time-scale is quantified over 26 AERONET stations located in eight geographically distinct regions by using statistical parameters. Overall DOD seasonal variation is fairly well simulated by MACC-II in all regions, although the correlation is significantly higher in dust transport regions than in dust source regions. The ability of MACC-II in reproducing dust vertical profiles has been assessed by comparing seasonal averaged extinction vertical profiles simulated by MACC-II under dust conditions with corresponding extinction profiles obtained with lidar instruments at M'Bour and Santa Cruz de Tenerife, and with CALIOP.This work has been supported by EU-project Monitoring Atmospheric Composition and Climate (MACC-II) under the European Union Seventh Framework Programme, grant agreement number 283576. J. M. Baldasano and S. Basart acknowledge the Severo Ochoa (SEV-2011-00067) program of the Spanish Government and the mobility program from the Catalan Government (BE-DGR 2012)

Social Models for Dealing with Inequalities

Production of INCASI Project H2020-MSCA-RISE-2015 GA 691004This chapter compares social models in Europe and Latin America. The goal is to study the interaction between two institutions: on the one hand, pre-distributive (ex ante) institutions, such as the structure and coverage of collective bargaining and, on the other hand, post-distributive (ex post) institutions, such as unemployment protection and social policy. Pre-distributive institutions are important for correcting inequalities in the labour market, because they introduce guidelines for egalitarian wage structures. Post-distributive institutions help to mitigate inequalities generated in the labour market. The methodology is based on statistical analysis of a series of indicators related to pre and post-distributive policies. The results present three types of model: (1) coordinated economies, typical of neo-corporatist Scandinavian countries; (2) mixed economies, typical of Mediterranean systems, and (3) uncoordinated economies, which equate to liberalism and the Latin American 'structural heterogeneity' model. It is neo-corporatist coordinated economies that generate the most pre and post-distributive equality. In turn, uncoordinated economies, and Latin American ones in particular, generate more inequalities due to highly informal employment and the weakness of their post-distributive institutions