Abstract. Local peoples from Niakhar in the Senegalese peanut basin highlight a dramatic increase of water access problems due to marked rainfall deficits and salinization of surface and ground water resources. The chemical quality of groundwaters is often critical because of the salinization process, whereas water surfaces, which should be used in such situations, are up early. More and more, lowlands and rivers beds are pervaded by salt crusts. Then the salinization of wells is increasing, leading to the extension of tans (salty of acidified soils). To study the impacts of climatic pejoration on the agroecosystems and on the living conditions of the populations, we carried out the analysis of the time series of the precipitations with daily and annual time steps from 1950 to 2015 on 6 meteorological stations, in situ measurements on 78 wells for an area of 311 km2, as well as local population interviews and field observation. The results confirm an important climatic break in the region in 1970. The long dry period, from 1970 to 2009, has increased the annual rain variability, decreased the number of rainy days per year. We confirm a real and large extension of well salinization, and salt crusting in the lowlands and the riverbeds. From the local people, it seems the process of degradation of the aquifers continues to progress from a large tidal event in 1984. The rainfall increase noted in the last decade does not seem to be enough to reverse the trend and to ensure both the rise of the piezometric level of the aquifers and the desalinization of surface and ground waters.
Dans le bassin arachidier (en zone soudano-sahélienne) et particulièrement dans le bassin de Thysse Kaymore, le déficit pluviométrique continu et prononcé depuis les années 1970 et la pression démographique croissant ont conduit à la dégradation des ressources en eau, rendant d e p l u s e n p l u s difficile l 'accès à l'eau. Les eaux souterraines sont souvent très profondes, alors que les eaux de surface qui devraient servir de recours dans de pareilles situations connaissent un tarissement précoce. Dans ce petit bassin de 162km 2 , le déboisement massif, la mise en culture de zones marginales et la disparition de la jachère conjugués au contexte climatique défavorable et à la pression démographique ont entrainé la dégradation du réseau hydrographiques et modification du fonctionnement hydrologique. Pour étudier les impacts de la péjoration climatique et de la pression anthropique sur les ressources en eau du bassin de Thysse Kaymore et sur les conditions de vie des populations, nous avons effectué l'analyse des séries chronologiques des précipitations de 1918 à 2011, des m esur e s pi éz om ét r i qu es a i n si qu e d es d é bi t s. Pour l'analyse diachronique de l'évolution des espaces ruraux des images Landsat de 1986, 1996, 2007 et 2016 sont utilisés. Les déficits pluviométriques annuels varient entre 54 et 60%. On constate un abaissement du niveau des nappes phréatiques, le tarissement précoce des puits, l'assèchement et l'ensablement des bas-fonds, une profondeur importante du niveau de l'eau sous le sol (58 à 116m pour le Continental Terminal et 300m pour le Maestrichtien) dans cette zone rurale ou les eaux souterraines sont les principales sources d'approvisionnement en eau des populations. A cette péjoration pluviométrique, il faut ajouter la forte pression démographique avec l'augmentation de la population qui a doublé en 30 ans (de 9400 habitants en 1976 elle est passée à 22524 en 2013) entrainant la multiplication des besoins en eau. Nonobstant ces problèmes accrus d'approvisionnement en eau potable des populations, cette zone constitue un bassin agricole, dont 62% des 90,76% de sa superficie cultivable sont exploités. Dans le même temps, on note le développement du maraîchage, une activité fortement consommatrice d'eau. Les besoins futurs en eau seront donc en croissance. Il
<p>In Senegal, the groundnut basin is the main agricultural region under a semi-arid climate, heavily cultivated in an agrarian system combining agricultural rotation and agroforestry dominated by <em>Faidherbia albida</em> trees. The soils of the groundnut basin, essentially sandy, have a low water retention capacity. In this area, water is a limiting factor, and the climate variability represents an additional constraint on an already precarious agricultural production system. It is therefore essential to improve knowledge on water saving practices and soil humidity dynamics. The management of water resources in agricultural fields requires reliable information about soil hydraulic properties, which control the partition of rainfall into infiltration and runoff, and their spatio-temporal variability.</p> <p>To investigate the variability of soil hydraulic parameters we have carried out infiltration measurement in open space without tree and below tree canopies. A total of 24 infiltration measurements were carried out using an automatic single-ring infiltrometer in the nearby of each plot (4 measurements &#215; 6 plots), and after removing the first 10 cm of uncompacted sand. The infiltration tests were carried out in June, October and December, respectively before, during and after the crop season. We used the Beerkan Estimation of Soil Transfer Parameters (BEST) method to retrieve the soil hydraulic parameters from infiltrometer data and field measurements of soil porosity, initial and saturated soil water contents and soil bulk density.</p> <p>The statistical analysis of the data showed a high variability during the cultivating period, both in time and space, especially of the saturated soil hydraulic conductivity Ks. However, the Ks seems higher under tree cover, around 0.186 mm/s, for 0.167mm/s without any tree canopy influence. &#160;Despite the expected homogeneity of the investigated sandy soil, the presence of the perennials triggered a patchy distribution of soil hydraulic conditions. These preliminary results evidenced the importance of taking into account parameters variability and landscape structure when simulating soil water dynamics in the Senegalese groundnut basin.</p>
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