This study evaluates the economic feasibility of a biological control industry in Niger. Farmers in the Sahel region of Niger are vulnerable to high millet yield losses due to the millet head miner, and their pest control options are extremely limited. Researchers have begun to support small businesses which sell a beneficial insect (Habrobracon Hebetor) that is very effective in limiting millet yield losses due to the millet head miner. This study discusses a wide range of questions related to the economic prospects of these businesses using two main analytical methods, an economic feasibility assessment and an econometric analysis. The economic feasibility assessment provides budget analysis for the potential businesses and discusses business options for scaling, price setting, and organizing. A central question in this analysis is whether farmers can cooperatively purchase beneficial insects as a means of preventing free-riding. With free-riding as a prominent concern for businesses, this study also provides an econometric analysis of the factors that affect farmer's willingness-to-pay for beneficial insects. / Master of Science

Os solos brasileiros apresentam no geral alto grau de intemperismo e são caracterizados pelo baixo teor de fósforo (P) disponível às plantas, devido à forte ligação com os minerais do solo (oxi-hidróxidos de Fe e Al). Esse elemento muito importante no metabolismo vegetal necessita ser aplicado em grandes quantidades na forma de adubo fosfatado para obtenção de altas produtividades agrícolas. No entanto, a produção de fertilizante solúvel convencional, como é o caso do superfosfato triplo (SFT), envolve gastos elevados de energia e emprego de ácidos fortes, gerando resíduos com alto potencial de contaminação ao meio ambiente. A fim de eliminar a etapa de acidificação industrial, nosso objetivo foi avaliar um biofertilizante fosfatado (BF) produzido a partir da solubilização de fosfato de rocha de Araxá (pouco reativo), pelo fungo Aspergillus niger. Nesse trabalho, foi testada em plantas de milho: (i) a eficiência do BF como substituinte parcial de SFT; (ii) alterações morfológicas de raízes de milho causadas pelo fungo presente no BF. No primeiro teste, em esquema fatorial 6x2, foram aplicadas doses de BF a fim de substituir o SFT em 0, 25, 50, 75 e 100 %, mais controle sem aplicação de P. A aplicação ocorreu em dois métodos, localizado em linha e volume total do solo. Foram avaliados o peso de massa seca da parte aérea, teor e conteúdo de P no tecido vegetal, atividade da fosfatase ácida e índice Spad. Para a análise das alterações morfológicas de raízes, foram utilizados tubos rizothron preenchidos com areia, com a aplicação dos tratamentos em volume total. Os tratamentos foram: SFT; BF com fungo vivo; BF com fungo morto; controle sem P. As coletas da parte aérea e raízes correram a cada 7 dias, iniciando a contagem ao sétimo dia. Foram avaliadas a produção de matéria seca de raízes, da parte aérea, a área superficial de raízes, o volume radicular e as classes de diâmetro de raízes. As doses de substituição mais promissoras foram de 25 e 50%, representando 89,02 e 80,86% da produção vegetal do SFT e 88,67 e 81,81% do conteúdo de P no tecido vegetal, respectivamente, ambos em aplicação em volume total. A presença do fungo vivo no BF não proporcionou diferenças nos parâmetros analisados. Apesar de serem necessários mais estudos e adaptações no processo de produção, o BF se mostrou promissor na substituição parcial da adubação fosfatada com SFT. O uso de BF proporciona, através da sua composição, o aproveitamento de resíduos agrícolas de baixo custo e a utilização de jazidas nacionais de fosfato de rocha, as quais possuem baixa reatividade. / Brazilian soils generally are highly weathered and characterized by low phosphate (P) content available to plants, due to high affinity of P to soil minerals, specially oxi-hydroxides of iron and aluminium. This important element in vegetal metabolism is needed to be applied in great quantities as phosphate fertilizer in order to attain high crop yields. However, the production of soluble conventional fertilizers, such as triple superphosphate (TSP), is costly and employs strong acids, generating residues potentially harmful to the environment. In order to avoid industrial acidification, our aim was to access the performance of a phosphate biofertilizer (BF) obtained from the solubilization of Araxá phosphate rock (low reactivity) by the fungus Aspergillus niger, L.. The suitability of BF to corn plants was investigated for: (i) efficiency of BF replacing TSP and (ii) morphological changes in plant roots caused by the fungus present in the BF. In the first experiment, designed in a 6 x 2 factorial scheme, rates of BF were applied in order to replace 0, 25, 50, 75 or 100% of TSP plus a control without P addition. The fertilizer was applied in bands or thoroughly mixed with soil. Plant shoot dry mass, total P content accumulated in the shoot, acid phosphatase activity and Spad index were measured. In the second experiment, morphological changes in plant roots were evaluated using rizothron tubes filled with sand where BF was mixed thoroughly. The treatments were TSP, BF with living fungus, BF with dead fungus and the control without P addition. Plant shoot and roots were collected every 7 days, starting from the 7th day after emergence. We measured dry mass of shoot and root, root surface area, volume and diameter. We found that when applied in total soil volume, fertilizer mixtures containing 25 and 50% of BF, a 89 and 80.9% of the dry matter and 88.7 and 81.8% of P content compared to the addition of 100% of TSP, respectively. For the variables measured, there was no difference in the results when applying BF with alive or dead fungus. We conclude that although further studies and improvement in the BF production are needed, the use of BF as partial replacer for TSP fertilizer is promising. Furthermore, BF use allows the recycling of low cost agricultural residues and the utilization of national deposits of rock phosphate, which are low reactive.

Neste estudo foi avaliada a remoção de metil paration - inseticida e atrazina - herbicida presentes em água, em reatores de bancada, com fungos. A pesquisa foi dividida em quatro etapas: operação em batelada com metil paration e micélio fúngico, com e sem glicose; teste de toxicidade em placas com Aspergillus niger AN400; operação em batelada com os pesticidas atrazina e metil paration e esporos de Aspergillus niger AN400, com e sem glicose; e operação em reatores de leito fixo e fluxo ascendente. Na primeira etapa, a remoção de metil paration foi de 97% nos reatores sem glicose e 94% nos reatores com glicose com 32 dias de reação. Na operação em batelada, com esporos, um modelo cinético de primeira ordem representou bem a velocidade de decaimento de metil paration nesta fase, principalmente, nos reatores que continham glicose. Para os experimentos sem adição de glicose, a constante cinética foi de 0,063 &#177 0,005/h, enquanto que para os experimentos com glicose a constante foi de 0,162 &#177 0,014/h. Dessa forma, a adição de glicose resultou efetivamente em aumento na velocidade de conversão do inseticida. Na fase experimental, com atrazina e esporos de Aspergillus niger AN400, a presença do substrato primário (glicose) não teve influência na remoção de atrazina, sendo que os percentuais de remoção foram muito próximos aos percentuais encontrados nos reatores sem glicose. O estudo cinético, nessa fase com atrazina e esporos, revelou que para os experimentos sem a adição de glicose, o valor da velocidade de conversão de atrazina (RATZo) foi de 0,023/d, enquanto que para os experimentos com glicose (RATZo) foi 0,022/d. Portanto, a adição de glicose parece não ter influenciado significativamente a velocidade de remoção do herbicida por Aspergillus niger AN400. O teste de toxicidade demonstrou que metil paration e atrazina não inibiram o crescimento do fungo nas várias concentrações testadas, inclusive nas mais elevadas, que foram 60 mg/L e 25 mg/L para metil paration e atrazina, respectivamente. No reator de leito fixo a remoção de metil paration foi de 40% com 12 h de tempo de detenção hidráulica, e 0,5 g glicose/L. Porém, quando a concentração de glicose foi duplicada a remoção de metil paration diminuiu para 35%. Neste reator o pH se manteve na faixa ácida 3,4 a 5,2, considerada ideal para os fungos. Os resultados encontrados mostram a viabilidade dos fungos para remoção desses pesticidas, considerados persistentes no ambiente. / In this study the removal of methyl parathion was evaluated - insecticide and atrazine - herbicide present in water, in reactors with fungi. The research was divided in four stages: operation in batch reactors with methil parathion and micelium fungus, with and without glucose; toxicity test in plates with Aspergillus niger AN400; operation in batch reactors with the pesticides atrazine and methyl parathion and spore of Aspergillus niger AN400, with and without glucose; and operation in reactors of fixed bed and ascending flow. In the first stage the removal of methyl parathion was 97% in reactors without glucose and 94% in reactors with glucose in 32 days of reaction time. In the operation in batch with spores, a kinetic model of first order represented very well the speed of decline of the methyl parathion in this step, in the reactors that contained glucose, mainly. For the experiments without the glucose addition, the kinetic constant was 0,063 &#177 0,005/h, and for the experiments with glucose the constant was of 0,162 &#177 0,014/h. In that way, the glucose addition resulted in increase in the speed of conversion of the insecticide. In the experimental step with atrazine and spores of Aspergillus niger AN400, the presence of the primary substratum (glucose) didn\'t have influence in the atrazine removal, and the percentile removal lays very close to the percentile found in the reactors without glucose. The kinetic study, in that step with atrazine and spores, revealed that for the experiments without the glucose addition, the value of the speed conversion of atrazine (RATZo) was 0,023/d, and for the experiments with glucose (RATZo) was 0,022/d. Therefore, the glucose addition seems not to have influenced significantly the speed of removal of the herbicide for Aspergillus niger AN400. The toxicity test demonstrated that methyl parathion and atrazine didn\'t inhibit the growth of fungi in the several concentrations, including in high concentrations, that were tested 60 mg/L and 25 mg/L to methyl parathion and atrazine, respectively. The reactor of fixed bed got removal of methyl parathion of 40% in 12 hours of detention hydraulic, in 0,5 g glicose/L. However, when the glucose concentration was doubled the removal of methyl parathion decreased to 35%. In this reactor the pH kept in the acid strip (3,4 - 5,2), considered ideal for the fungi, and conductivity values didn\'t favor the hydrolysis of the insecticide. The found results show the viability of the fungi for removal of those pesticides, considered recalcitrant to the environment.

Os solos brasileiros apresentam no geral alto grau de intemperismo e são caracterizados pelo baixo teor de fósforo (P) disponível às plantas, devido à forte ligação com os minerais do solo (oxi-hidróxidos de Fe e Al). Esse elemento muito importante no metabolismo vegetal necessita ser aplicado em grandes quantidades na forma de adubo fosfatado para obtenção de altas produtividades agrícolas. No entanto, a produção de fertilizante solúvel convencional, como é o caso do superfosfato triplo (SFT), envolve gastos elevados de energia e emprego de ácidos fortes, gerando resíduos com alto potencial de contaminação ao meio ambiente. A fim de eliminar a etapa de acidificação industrial, nosso objetivo foi avaliar um biofertilizante fosfatado (BF) produzido a partir da solubilização de fosfato de rocha de Araxá (pouco reativo), pelo fungo Aspergillus niger. Nesse trabalho, foi testada em plantas de milho: (i) a eficiência do BF como substituinte parcial de SFT; (ii) alterações morfológicas de raízes de milho causadas pelo fungo presente no BF. No primeiro teste, em esquema fatorial 6x2, foram aplicadas doses de BF a fim de substituir o SFT em 0, 25, 50, 75 e 100 %, mais controle sem aplicação de P. A aplicação ocorreu em dois métodos, localizado em linha e volume total do solo. Foram avaliados o peso de massa seca da parte aérea, teor e conteúdo de P no tecido vegetal, atividade da fosfatase ácida e índice Spad. Para a análise das alterações morfológicas de raízes, foram utilizados tubos rizothron preenchidos com areia, com a aplicação dos tratamentos em volume total. Os tratamentos foram: SFT; BF com fungo vivo; BF com fungo morto; controle sem P. As coletas da parte aérea e raízes correram a cada 7 dias, iniciando a contagem ao sétimo dia. Foram avaliadas a produção de matéria seca de raízes, da parte aérea, a área superficial de raízes, o volume radicular e as classes de diâmetro de raízes. As doses de substituição mais promissoras foram de 25 e 50%, representando 89,02 e 80,86% da produção vegetal do SFT e 88,67 e 81,81% do conteúdo de P no tecido vegetal, respectivamente, ambos em aplicação em volume total. A presença do fungo vivo no BF não proporcionou diferenças nos parâmetros analisados. Apesar de serem necessários mais estudos e adaptações no processo de produção, o BF se mostrou promissor na substituição parcial da adubação fosfatada com SFT. O uso de BF proporciona, através da sua composição, o aproveitamento de resíduos agrícolas de baixo custo e a utilização de jazidas nacionais de fosfato de rocha, as quais possuem baixa reatividade. / Brazilian soils generally are highly weathered and characterized by low phosphate (P) content available to plants, due to high affinity of P to soil minerals, specially oxi-hydroxides of iron and aluminium. This important element in vegetal metabolism is needed to be applied in great quantities as phosphate fertilizer in order to attain high crop yields. However, the production of soluble conventional fertilizers, such as triple superphosphate (TSP), is costly and employs strong acids, generating residues potentially harmful to the environment. In order to avoid industrial acidification, our aim was to access the performance of a phosphate biofertilizer (BF) obtained from the solubilization of Araxá phosphate rock (low reactivity) by the fungus Aspergillus niger, L.. The suitability of BF to corn plants was investigated for: (i) efficiency of BF replacing TSP and (ii) morphological changes in plant roots caused by the fungus present in the BF. In the first experiment, designed in a 6 x 2 factorial scheme, rates of BF were applied in order to replace 0, 25, 50, 75 or 100% of TSP plus a control without P addition. The fertilizer was applied in bands or thoroughly mixed with soil. Plant shoot dry mass, total P content accumulated in the shoot, acid phosphatase activity and Spad index were measured. In the second experiment, morphological changes in plant roots were evaluated using rizothron tubes filled with sand where BF was mixed thoroughly. The treatments were TSP, BF with living fungus, BF with dead fungus and the control without P addition. Plant shoot and roots were collected every 7 days, starting from the 7th day after emergence. We measured dry mass of shoot and root, root surface area, volume and diameter. We found that when applied in total soil volume, fertilizer mixtures containing 25 and 50% of BF, a 89 and 80.9% of the dry matter and 88.7 and 81.8% of P content compared to the addition of 100% of TSP, respectively. For the variables measured, there was no difference in the results when applying BF with alive or dead fungus. We conclude that although further studies and improvement in the BF production are needed, the use of BF as partial replacer for TSP fertilizer is promising. Furthermore, BF use allows the recycling of low cost agricultural residues and the utilization of national deposits of rock phosphate, which are low reactive.

Au cours de cette thèse, des outils théoriques (simulation) et expérimentaux (tracking) ont été développés afin d’établir les mécanismes sous-jacents aux phénomènes de choix collectifs d’exploitation de sources de nourriture et à la gestion collective des stocks de nourriture constitués au sein d’une colonie de fourmis. Le premier volet de mon travail révèle l’influence de caractéristiques physiques (telles que l’angularité et la topographie) des pistes entre le nid et les sources de nourritures, sur les comportements des fourmis au niveau individuel et leur résultante au niveau collectif en termes d’exploitation de ressources alimentaires. Le second volet de ma thèse est consacré aux dynamiques et régulations à l’œuvre au sein des phénomènes de dissémination collective et d’accumulation de nourriture au niveau intranidal. Les réseaux de distributions et d’échanges, reconstitués chez différentes espèces grâce à un marquage individuel et dans différents contextes montrent des similarités inattendues, notamment en termes d’hétérogénéités interindividuelles et de robustesse face à la variabilité des ressources. / During my PhD I have developed theoretical (simulation) and experimental (tracking) tools to investigate the mechanisms underlying the collective food source choice as well as collective food management at the intranidal level in ants. A first part of my thesis reveals the influence of the physical (and in particular the angularity and the topography) properties of the trail to the food source on the ant behavior at the individual level and its resulting food source choice/exploitation at the collective level. The second part of my thesis is dedicated to the dynamics of the food flow entering the nest, its regulation and the food dissemination/accumulation processes at the intranidal level through trophallaxis (mouth-to-mouth fluid exchange). The networks of food distributions and exchanges were built for two ant species in various experimental conditions. Interestingly, all theses networks show several similar properties, such as a high degree of heterogeneity in the individual participation to the food exchange activity as well as a robustness facing environmental variabilities.

Cette thèse traite d’une série de dynamiques identitaires qui marquent le pays Hausa nigérien contemporain. Elle est fondée sur trois missions d’enquêtes ethnographiques, conduites au Niger entre janvier 2006 et décembre 2008. La prise en compte de l’extrême mobilité des populations au Niger a également conduit à effectuer un travail de terrain auprès de la communauté nigérienne implantée en Belgique. Notre approche est une ethnographie attentive aux dynamiques de matérialisation des identités, aux pratiques et aux objets par lesquels les personnes et les communautés qui se revendiquent « hausa » rendent effective une telle affirmation. Il s’agit également d’interroger, dans leur rapport aux dynamiques de l’identité, les flux migratoires, commerciaux et médiatiques qui traversent les espaces urbains et ruraux du Sahel nigérien. Notre recherche vise à saisir la dynamique d’hausaisation (expansion de la langue hausa et des pratiques perçues comme hausa) qui marque les paysages identitaires du Niger. Cette dynamique est analysée au travers des stratégies de reconversion identitaire de migrants touaregs, le plus souvent de basse classe, implantés dans les villes de Sud. Elle est également illustrée par le peuplement de l’un des quartiers périphériques de Niamey. Cet espace présente, en effet, la caractéristique d’être pris dans une dynamique d’hausaisation qui soit à la fois bien avancée et relativement récente. Enfin, ces dynamiques sont analysées par le prisme du « réveil islamique » qui, depuis la fin des années 1970, marque le pays Hausa. Il s’agit notamment de montrer comment ce réveil islamique est fonction de la place occupée par le kasar hausa au sein des géographies globales de l’islam contemporain.

Univ., Diss.--Hohenheim, 2000. / Literaturverz. S. 125 - 132.

Thesis (doctoral)--Université de Bordeaux III, 1982. / Includes bibliographical references (p. 1233-1281) and index.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O conhecimento da biodiversidade e bioprospecção de novos micro-organismos tornaram-se um dos focos principais da era biotecnológica, visto que a utilização destes organismos na busca de soluções nas áreas de alimento, saúde, meio ambiente e indústria vem crescendo de forma acelerada no atual cenário mundial. A utilização de micro-organismos é tida como uma potencial alternativa para a biotecnologia ambiental e industrial. A presente proposta visa gerar informações acerca dos mecanismos fisiológicos, através da avaliação dos aspectos relativos ao crescimento, proteínas totais, acumulação de polifosfato, atividade das enzimas extracelulares, sistemas antioxidante enzimático e remoção do metal, por Aspergillus niger UCP/ WFCC 1261, isolado da caatinga, em função da indução de estresse oxidativo por cobre no meio de cultivo. O isolado foi cultivado em meio Sabouraud, contendo cobre, nas concentrações de 0,5 mM; 1mM e 2 mM durante 15 dias, sob a temperatura de 28 C. A variação do polifosfato, proteínas totais e atividades das enzimas antioxidantes, foram avaliadas em função do cultivo nos diferentes meios, na presença e ausência do metal. Para as determinações das atividades das enzimas extracelulares foram utilizadas metodologias específicas, durante o crescimento na ausência e em presença do íon metálico. Os aspectos morfo-ultraestruturais foram analisados sob microscopia de luz e microscopia eletrônica de varredura. Os resultados obtidos fornecem informações essenciais para o entendimento da diversidade microbiana, bem como dados acerca do comportamento do micro-organismo frente ao cobre com sua potencial aplicação nos processos biotecnológicos associados à remediação de ambientes poluídos com cobre. / The knowledgement about the biodiversity and the bioprospection of new microorganisms are the main focus of the biotechnological age, since the use of these organisms in the areas of food, health, environment and industry is increasing in the current world-wide scene. The use of microorganisms is one alternative potential for ambient and industrial biotechnology. Present proposal aims at to provide informations about the physiological mechanisms by using the evaluation of growth, accumulation of polyphosphate, total proteins, extracellular enzyme activity, antioxidant enzyme systems and metal renoção by Aspergillus niger UCP / WFCC 1261, isolated from caatinga, depending on the induction of oxidative stress by copper in the culture medium. The isolate was grown on Sabouraud medium containing copper at concentrations of 0.5 mM, 1 mM and 2 mM for 15 days under a temperature of 28 C. The variation of polyphosphate, total protein and antioxidant enzyme activities were measured as a function of cultivation in different media in the presence and absence of metal. For the determination of enzyme activities, extracellular specific methodologies were used during growth in the absence and presence of the metal ion. Morphological and ultrastructural aspects were analyzed by light microscopy and scanning electron microscopy. The results could be used to generate essential knowledge related to the behavior understanding face the copper presence and its potential application in the biotechnological processes related to environment remediation polluted with the heavy metal.

Malgré le déficit pluviométrique persistant qui le caractérise depuis plus de quarante ans, le Sahel connaît un accroissement notoire du ruissellement, des écoulements et de l'érosion hydrique. On attribue cela aux changements d'usage des sols, et à une fatigue de ceux-ci, épuisés par des successions de cultures de moins en moins suivies de phases de repos. Cela se traduit par une dégradation rapide des sols, dont le processus le plus courant est l'encroûtement. C'est ce même encroûtement qui est à l'origine de l'augmentation des écoulements. On se propose ici de déterminer quelle est l'évolution de l'occupation des sols dans une région de l'Ouest du Niger, afin de comprendre les facteurs et les processus qui aboutissent à de très nettes modifications dans le régime des eaux ; outre l'augmentation des débits et des coefficients d'écoulement, on observe une diminution des temps de réponse des sols et des bassins aux précipitations. Ceci est directement lié à la diminution de la capacité des sols à retenir l'eau, qui est elle-même due à l'encroûtement. L'évolution de l'occupation des sols est donc l'explication qui permet de comprendre les modifications du cycle de l'eau. On utilise ici la télédétection pour parvenir à déterminer cette évolution des usages des sols. Au passage, on essaie d'y voir plus clair sur le reverdissement observé et mesuré par de nombreux chercheurs : est- il tangible ? Dans quelles régions ? Sur quelles durées ? Quel est le rôle des méthodes de classification dans la mise en évidence de ce reverdissement ? Il faut aussi s'assurer de la représentativité des zones d'entraînement utilisées. Des méthodes de l'hydro-géomorphométrie sont appelées au secours pour séparer la zone d'étude en deux ensembles distincts (plateau- non plateau) pour faciliter la classification. Une étude par photo-interprétation est tentée sur le degré carré de Niamey, dans l'optique d'avancer dans la distinction du rôle respectif de la sécheresse et des activités socio-économiques dans les changements d'usage des sols. Enfin, après avoir comparé nos travaux avec les très nombreuses études déjà réalisées dans cette région, on s'intéresse à l'impact des changements d'usage des sols sur l'infiltration et le ruissellement, de l'échelle de la parcelle à celle du grand bassin versant, en particulier sur l'évolution remarquée des débits et régimes des fleuves, et de l'accroissement du risque de crue, observé ces dernières années. Il semblerait que 2 à 5% de surface de sol encroûté sur un bassin suffise à accroître et concentrer suffisamment les débits pour accroître cet aléa, sans pour autant empêcher un certain « reverdissement » global, tel qu'observé par l'évolution des indices de végétation télédétectés. / Despite the persistent rainfall deficit observed from more than forty years, the West African Sahel exhibits a significant increase in runoff, in rivers discharge and in water erosion. This fact is attributed to land use changes, particularly to soil overexploitation, characterized by the shortening of fallow periods. This leads to the degradation of soil structure, and to soil crusting. The soil crusting is the first factor of the increase in runoff. The purpose of this research is to determine the land use evolution in the western part of the Niger, to underline the factors and processes leading to the significant changes in surface water regime. The increase in discharges and runoff coefficients is accompanied with a reduction in the lag time of the slopes and basins when occurs a rainy event. This is directly linked to the decrease in soil water holding capacity, due to soil crusting. Hence, land use/land cover evolution is the main explaining factor of water cycle changes. Remote sensing is used in order to determine land uses changes. This implies to improve the knowledge about the “regreening” of the Sahel, observed and measured by several research teams: is it a myth or a reality? In what regions? During what periods? What is the role of classification methods of remote sensing in the highlighting of the regreening? We need to ensure that regions of interest used in this study are representative of the regional area. Methods of “hydro-geomorphometry” are needed to divide the study area into two differents areas, “plateau” and “non-plateau”, in order to avoid errors in the pixel classification of some different vegetation types which have neighbouring NDVI. A study by interpretation of aerial photographs is attempted over the Square degree of Niamey, with the aim of improving the separation between the respective role of the drought and the human activities in the evolution of land cover. After a comparison of our research with numerous previous studies realised on the same region, we perform an analyse of the impact of land use changes on infiltration and runoff, from the plot scale to the great basin scale, with a special focus on the observed evolution of rivers discharges and regimes and on the increase in flood hazard, detected during the last years. It appears that 2 to 5% of the total area exhibiting soil crusting are sufficient to increase and concentrate enough the discharges and to provoke a significant rise in the flooding, without avoiding a certain global “regreening” such as it is observed using the evolution of vegetation indices.