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The modernization of irrigation in Mediterranean countries has boosted irrigated agriculture. Undoubtedly, this transformation has increased performance levels, but new compelling challenges have arisen: (i) in many situations, the irrigation performance gap remains much greater than expected; (ii) irrigation intensification and expansion are at the root of pollution of valuable ecosystems and overdraft of non-renewable water resources; (iii) water savings are not as foreseen due to unexpected rebound effects of irrigation efficiency improvements; (iv) modern energy-eager pressurized systems are costly and environmentally questionable. Furthermore, it is now clear that climate change and its foreseen variability will accentuate the vulnerability of agriculture and ecosystems. The main objective of the innovation hub presented here is to favour the emergence, evaluate and boost innovations aiming at reducing the performance gap and thus improve the sustainability of irrigation systems in the Mediterranean region. These innovations comprise new tools and services for farmers and water users associations, designed to increase water, nutrient and energy use efficiency. Innovation development leading to adoption of new standards will rely on bottom-up processes, understanding of governance settings and implementation of sharing procedures, through innovation hubs developed by the project.

Unsustainable use of water resources and climate change will exacerbate the already existing tensions on resources, especially in the Mediterranean context. Despite investments in modern, economically and energetically costly equipment, the performance of irrigated agriculture remains below expectations, notably because of the lack of water data available and limited use of decision support tools. Access to information at an unprecedented level, via easily accessible low-cost and low-tech sensors, may be a major lever for better identifying achievable performance gains, at different spatial and temporal scales, and for guiding the choice of actors towards more virtuous practices. To explore this hypothesis, two Mediterranean irrigated systems (Provence, France, and Cap Bon, Tunisia) with major water use efficiency issues were selected. The agrarian diagnosis revealed the main local needs and constraints that limit sustainable water management. Innovative technological systems (water sensors, automation, IoT networks) have been developed in response and implemented on field through a participatory approach. The technologies have been designed to be low energy, low-tech and low-cost, based on the hypothesis that the lack of accessibility - investment and O&M costs, system readability - of existing equipment was a brake to the dissemination of innovations in the agricultural sector, especially in the global South. We believe that the adoption of such technologies will contribute to improve irrigated systems sustainability by playing on several dimensions: supporting decision- making and promoting suitable and sparing water use; maintaining agricultural production and economic results of production systems by reasoning the inputs; improving water users labour conditions; generally, accompanying the transition towards more virtuous practices, by making the quantification of the flows, and thus the understanding and experimentation, accessible to the irrigated territory stakeholders. The performance gains achievable with these innovations, heeding their inherent weaknesses (eg. lower robustness and accuracy), and the potential impacts of their adoption at larger scale remain to be assessed in an integrated way.

Vegetable crops production in the southern Mediterranean is facing two major challenges: i) producing high quantities of products in a context of climate change; ii) reducing the environmental impacts, result of intensive fertigation strategies often promoted by public policies. The objectives of this study were first to assess the fertigation strategies implemented by farmers to grow chili-pepper, in the Merguellil downstream plain, a highly crop-diversified irrigated area of Central Tunisia, then to investigate alternative and more efficient fertigation scenarios. Different methods of data acquisition (surveys, field monitoring, direct observation, laboratory analyses) were used, to collect management data for eleven chili-pepper fields (selected based on local diversity of management rules). The Optirrig crop model was used to represent the fertigation strategies and the resulting hydroagronomical processes (e.g. water drainage, nitrate leaching, crop growth, water and nitrogen stress). An automatic fertigation strategies optimization process was performed to achieve two typical contradictory objectives: increased yields and reduced water and nitrogen losses. The investigations revealed that several fertigation strategies are implemented, almost all relying on the use of high amounts of water and resulting in massive drainage and nitrate leaching. However, in some cases, farmers were able to achieve high productivity with relatively low amount of resource. By performing the automatic optimization process, an improved design of fertigation strategies (frequency, doses) in coherence with soil properties was found to be relevant to simultaneously improve yields (by 1 to 4 T.ha-1, depending on fields) and drastically reduce losses (water, nitrogen).

En Tunisie, des politiques récentes cherchent à mettre en place une participation effective des populations rurales à la formulation de plans territoriaux de développement intégrant des dimensions économiques, sociales et environnementales. Le programme PACTE expérimente une démarche pilote pour mettre en oeuvre cette participation dans six zones rurales, grâce à la constitution de comités de territoire. Pour préparer le travail de chaque comité, des habitants ont participé à la réalisation d’un diagnostic de leur territoire pour identifier les principaux enjeux de développement. Ensuite, ils ont formulé des propositions d’action pour répondre à ces enjeux, verbalement lors d’ateliers et, en dehors des ateliers, en utilisant des fiches mises à leur disposition puis collectées. L’article analyse les actions proposées par des habitants d’une zone d’intervention située dans le gouvernorat du Kef. L’analyse porte sur : i) les finalités de ces actions, à savoir dans quelle mesure ces actions répondent aux enjeux identifiés ; et 2) les caractéristiques de ces actions, notamment leur dimension individuelle ou collective et leur degré d’innovation. L’analyse est basée sur les comptes rendus des ateliers, les fiches de propositions d’actions collectées, et des entretiens auprès de membres d’institutions publiques de développement. Les actions proposées par les habitants couvrent l’essentiel des enjeux identifiés au cours des ateliers. Parmi les fiches remplies, ces habitants donnent la priorité à des actions individuelles et génératrices de revenu et, en particulier, à des activités qu’ils pratiquent déjà. Lors des ateliers, les participants ont envisagé des actions plus diverses, parfois innovantes, et plus souvent de nature collective. L’analyse proposée ici a permis d’identifier des opportunités pour la production de connaissances communes entre les futurs membres des comités de territoire, et entre eux et les membres des institutions publiques de développement. Le projet PACTE constitue une expérience innovante de mise en oeuvre d’une démarche participative à grande échelle pour le diagnostic territorial et la formulation de proposition d’action en zone rurale au Maghreb. La réflexion sur les méthodes et moyens à utiliser pour permettre cette participation est un chantier sur lequel il sera important de continuer à avancer dans les années à venir.

The challenge of agriculture in the up-coming decades is to feed an ever-increasing population while reducing or getting rid of chemical inputs and preserving biodiversity and natural resources. In arid and semi-arid areas of the Mediterranean basin, farmers have to face this challenge, alongside multiple environmental and climatic risks. Due to low rainfall, irrigation is instrumental for agriculture and consequently for economy, in these areas. So far, irrigation has been analyzed in terms of eco-efficiency, and is commonly associated with intensification and pollution. First, this study aimed to identify, in a semi-arid irrigated area, a set of farming practices, already implemented by farmers, with agroecological potentials. We present in this communication two “virtuous” farming systems, compared to more conventional and intensive systems. Second, based on the results from 65 semi-structured interviews, a hypothetical plot with a more agroecological management style was designed. The study was carried out in the Merguellil irrigated plain in Central Tunisia, which is entirely cultivated, with a wide variety of crop types such as horticulture, fruit trees and cereals. A first farmer installed at the plot scale, a relay cropping of fava bean (Vicia faba) with pepper (Capsicum annuum) in intercropping with olive trees (Olea europaea). In this agroforestry system, the plot was further surrounded by a windbreak cereal (sorghum) belt. The farmer used old and local varieties, very resistant to pest attacks and that require low chemical inputs, resulting in lower cost of production. Seeds were saved and reused. At the farm level, crop residues (pepper, fava bean, olive tree pruning residue) and cereals were used for livestock feeding. Another farmer used manure as an organic fertilizer after a fermentation process. This practice lead to a substantial reduction of chemical nitrogen fertilizer use. In addition, he applied a water stress period at the beginning of the cycle, in order to “stimulate root growth and improve the plant's absorption capacity”. This allowed him to avoid the use of a root growth accelerator. In both cases, different types of spatial crop rotations and successions were set up with frequent fallow periods in order to restore soil fertility. However, these interesting practices coexist with other less virtuous practices. For example, most farmers continued to intensively apply pesticides and used very high quantities of chemical fertilizers. These farmers were mostly specialized in market garden and fruit trees, extremely water consuming. They generally used high yielding varieties, less resistant to pest attacks. Furthermore, the study showed that farmers usually combined agroecological practices for different purposes: i.e. income increase, soil fertility improvement, land-use optimization. All the practices mentioned above could be combined on a single plot/farm, giving a hypothetical system with a more agroecological orientation. With an adapted water and fertilization management, such a system could improve water and fertilizer efficiency and maintain soil quality. But this may not necessarily lead to better pest control or better yields. These practices remain to be evaluated, and would be adopted by farmers only if they see it as a clear interest.

Irrigated agriculture is a major feature of the Mediterranean basin, and has expanded tremendously in the past decades, through access to a previously untapped resource, groundwater. Within the perspective of global challenges linked to food security, poverty alleviation, natural resources degradation in conjunction with climate change, rural development and migration patterns, irrigated agriculture is of vital importance to maintain viable farming systems within the Mediterranean basin. In addition to the imminent threat of groundwater depletion, small-scale irrigated farming systems face vulnerabilities such as soil degradation, unequal access to productive resources and difficult access to markets and information. VIANA extends previous research on vulnerabilities of irrigated agriculture in North Africa, by characterizing potentially existing local agroecological solutions and understanding the context in which such practices have emerged or been adopted. Using the lens of vulnerability and adaptive capacity, and assuming that, locally, strong capacities of adaptations and innovations developed by farmers exist, the objective of this project is to identify, characterize and co-evaluate existing adaptations and lower-input systems developed by actors at different scales (plots, farms and irrigated territory) to deal with these vulnerabilities. The project will, in particular, focus on characterizing local farming practices with a potential to maintain overall productivity of irrigated territories while improving environmental sustainability, focusing in particular on on-farm improved efficiency of input uses, water efficient cropping systems, and crop-animal diversification strategies. The project involves three contrasted groundwater-irrigated territories in North Africa: the Saïs plain in Morocco, the Haut-Chéliff plain in Algeria, and the Kairouan plain in Tunisia. From a methodological point of view, the project is resolutely transdisciplinary, and will include researchers in agronomy, water and environmental sciences, economy and political science. All these disciplines will contribute to qualify the socio-ecological system of irrigated agriculture within an interdisciplinary cognitive framework. It is also problem and action-oriented and participatory, with an emphasis on social learning, through the inclusion of farmers and institutional actors in major steps of the project. Involving six young researchers from four Mediterranean countries, in various fields of knowledge, VIANA will contribute to forming a new generation of researchers interested in apprehending challenges around irrigated agriculture, in a transdisciplinary and participative approach. In parallel, it will contribute to improve farmers' knowledge on environmental impacts of agriculture through both the social learning process and a better understanding of their roles and actions in the research arena.

In the irrigated plains of North Africa, the sustainability of productive resources is subject to several threats linked to the productivist model of irrigated agriculture. These threats prompt farmers to mobilize depleting productive resources. In order to reduce vulnerabilities and sustain their farming systems, farmers can update their adaptive strategies by setting-up innovative, alternative, farming practices that in conjunction enable them to sustain farm profitability. This study aims at mapping and analyzing such existing local farming practices with agroecological potentials. Our approach is based on direct observations combined with interviews with farmers in three irrigated plains in the Maghreb: the Merguellil, Upper Cheliff and Saiss plains, respectively in Tunisia, Algeria and Morocco. This study shows that, while intensive agricultural practices do characterize most farming systems, there co-exists, at the same time, a wide range of alternative practices that valorize ecological processes in some way or another. The most common practices are developed to improve soil fertility management (production of diluted liquid manure, organic fertilization, integration of leguminous plants into the rotation), to enhance land use efficiency (crop rotation, intercropping, relay intercropping, agroforestry) or to provide multiple ecosystem services (diversification, livestock integration). For example, and in the sense of “hitting two targets with one shot ”, farmers combine two or more crops on the same plot in order to (1) increase land-use efficiency to face land fragmentation linked to inheritance issues; (2) diversify their cropping strategy and spread out market-related risks; (3) reduce expensive production costs related to irrigation, chemical fertilization, etc. Our analysis of farmers' logics shows that economic reasons undoubtedly take precedence overall environmental concerns. This is why these innovative practices are considered as (1) access to low-input and low-cost strategies for small farmers; (2) as a pathway to international markets for agribusiness farmers, rather than agroecological practices per se. In plains like those of the Maghreb, intensive and conventional practices, associated with environmental threats, coexist with a wide variety of practices with agroecological potentials. Putting the farmer first and mobilizing their extensive local knowledge can contribute to the field of agroecology. Such practices may pave the way for a more sustainable agricultural development.

Efficient use of water and nutrients in irrigation system is important in arid and semi-arid regions, where water is a limiting resource. This study aims to analyze irrigation and fertigation practices for a widespread crop (pepper, Capsicum annuum) in Tunisia, in a context of highly diverse agricultural practices. The study took place in the irrigated plain of the Merguellil river in Central Tunisia, characterized by its high diversity of crops and practices. In 2019, irrigation and fertilization practices involved in pepper crop cultivation watered by drip irrigation, were compared on fourteen plots. This was carried out through an approach coupling semi-directive surveys with farmers and monitoring of irrigation, done using a temperature logger installed on the irrigation pipes and allowing the detection of irrigation duration. The study covered the three main seasons of pepper cultivation (Spring, Summer and late Summer). The results showed globally an opposition of two main logics. On the one hand, there are strategies aiming to a significant water supply during the first days after planting, followed by a non-irrigated period, forcing the plant to "tap into the soil water reserves", then irrigation at regular rates (once every three to five days or more) thereafter, sometime alternate with fertigation. On the other hand, there are strategies of regular water and nutrients supply, taking into account crop requirements: low water inputs at the beginning (on daily or once every two to four days rate), followed by a progressive increase. In this strategy, application of fertilizers through the drip irrigation occurred right after the first irrigations, the farmer alternating up to three irrigations for one fertigation. Commonly, fertilization was fractioned and application was done in the last quarter of watering time in order to avoid/reduce nutrient leaching. The number of splits varied significantly from a farmer to another and from a strategy to another. These irrigation and fertigation practices may have different effects on the system outputs, mainly on water and nitrogen efficiency and yield.

Irrigated agriculture is instrumental for the economy and employment in North Africa countries. However, farmers in the Maghreb region face, on the one hand, multiple environmental and climatic risks, and on the other, economic constraints that, combined together, can lead to the vulnerability of these rural populations. Assuming that strong capacities of adaptation and innovation potentials exist within small-scale irrigated farming systems, this study aimed to identify and characterize existing eco-efficient and resilient farming practices in the Kairouan irrigated plain in Central Tunisia. The latter is entirely cultivated, with a wide variety of crop types such as market gardening, arboriculture and cereals. Representative of small-scale family farming systems in the irrigated plains of Tunisia, this study site lends well to work on the characterization of agroecological practices in a semi-arid irrigated environment. Semi-structured interviews were conducted with farmers, first, to identify low-input practices at the plot and farm scale, second, to apprehend the determinants and the objectives of these practices. The sampling procedure sought to explore the wide range of existing practices, and was thus partly based on the farmers and the local agricultural administration knowledge and networks. The study shows that farmers usually combined different cropping systems, mostly for economic reasons (improved water and land use, increased monetary income by reducing chemical inputs). Low chemical-input or water-use practices, related to agroecology, were observed, especially for watermelon and pepper, which are commonly associated with leguminous species. Agroforestry practices, associating different tree species (mainly olive trees) to other crops, or intercropping (market gardening, cereals), were also common. Some farmers integrated animals in “a no lost integrated farming system”. Furthermore, a little-known, but very innovative practice observed, was irrigation using water coming from organic fermentation, leading to a significant reduction in the need of chemical inputs. All these practices, which are particularly present in small rural farmers, who represent the great majority of the farmers in Tunisia and in Maghreb, show the existence of knowledge on which an agroecological transition could be initiated. Identifying such local agroecological practices is a first step in their adoption and promotion, as decision makers increasingly seek to take into account the environmental impacts of agriculture in the Maghreb.

Ce Guide " Audit Territorial Participatif " a été élaboré par le CIRAD et ses partenaires de recherche et d'enseignement supérieur (IRSTEA, INAT, INRGREF) pour la Direction Générale de l'Aménagement et de Conservation des Terres Agricoles du Ministère de l'Agriculture et des Ressources Hydrauliques et de la Pêche (MARHP) tunisien. Il a été écrit à l'intention des agents de développement territorial travaillant directement avec les communautés locales. Il s'adresse plus particulièrement aux Chargés d'Appui au Développement Rural (CADR) du (MARHP) qui interviendront dans le Programme PACTE (Programme d'Adaptation au changement Climatique des Territoires vulnérables de Tunisie, 2018-2024), mais également de manière plus large à tout individu (agents de terrains, membres des communautés, consultants, vulgarisateurs) souhaitant s'investir dans des actions de diagnostic et de planification participative du développement à l'échelle de communautés locales. Ce guide pratique sur la démarche d'audit territorial participatif se veut opérationnel et facilement accessible. Il est structuré pour permettre à l'utilisateur d'aller directement au coeur du texte qu'il souhaite lire. Il est fait pour accompagner l'agent sur le terrain, et aménage des espaces pour qu'il puisse annoter le document et l'adapter à ses besoins spécifiques. On y trouvera la description d'une méthode d'analyse d'un territoire et des outils pratiques de mise en oeuvre de cet audit. Cette méthode a été conçue pour pouvoir intervenir dans des territoires vulnérables en Tunisie afin d'y mener des actions de planification participative pour une utilisation durable des ressources naturelles en vue du développement durable des communautés. Il est le produit de différentes expériences pratiques menées par le CIRAD et ses partenaires de recherche et de développement. Cette approche n'est pas la seule existante et s'appuie fortement sur différents cadres méthodologiques dont les références sont données en bibliographie. Elle est le fruit d'une confrontation des auteurs à différentes questions et problématiques de terrain. Elle a été conduite dans des cadres divers de recherche, de recherche/action ou de développement, en particulier en Tunisie et au Brésil.

The floodplain grasslands of the Tana River Delta, located on the East African coast in Kenya, form part of an intertwined socio-ecological deltaic system of high biodiversity value that delivers numerous goods and services. Dominated by Echinochloa stagnina (Retz) P. Beauv., a highly productive species adapted to seasonal flooding, this ecosystem is the major dry-season grazing grounds of the local pastoralist communities. The construction of hydroelectric infrastructure has led to a modification of the flooding regime. The impacts of the resulting reduction of floods in the deltaic zone on ecosystem properties and services still need to be assessed. In such a perspective, this study characterizes the link between the flooding regime of the Tana River and the growth pattern of its floodplain grassland. Aboveground dry phytomass was sampled for 15 months under a wide variety of naturally flooded and non-flooded conditions, irrigation and cutting frequency treatments. Annual aboveground dry phytomass attained high values between 11 T.ha-1 and 32 T.ha-1 and annual net primary production of the grasslands reached 35 T.ha-1.year-1. Growth rates clearly depended on the flooding regime, management and climate conditions and were on average more than twice as fast during, and 50% faster after the floods, relative to pre-flood conditions. A plant growth model allowed testing the effect of different flooding regimes on plant productivity, highlighting very low productivity in the absence of floods. These results suggest that rangeland and water management for the Tana River deltaic grasslands are tightly linked. The projected construction of another dam could lead to a reduction of flood extent and period, a decrease of grassland productivity and growth duration. Mitigation of this type of negative impacts, which will have direct and adverse consequences for the pastoralist communities as well as on the delivery of other goods and services, needs to be undertaken. (Texte intégral)

The Sahel is one of the regions in the world which has experienced the strongest climatic changes in the past decades. In a context of high population growth and mainly agriculture-based economies and livelihoods, these fluctuations can cause serious societal problems. Understanding past and predicting future climatic changes and their implications on natural and cultivated ecosystems are henceprimordial. Modelling efforts in the fields of hydrology and ecohydrology have already been undertaken, but are hindered by data availability as soon as the multi-decadal time scale is targeted. Indeed, in addition to being scarce, climatic data are often discontinuous in time, limiting the use of many modelling tools. In this study we produced a continuous and consistent data set at Niamey, Niger (13.5° N, 2.1° E) from 1950 to 2012 at different temporal scales (daily, 3-h and 30-min) that can be used as inputs in most LSM-type, vegetation and hydrological models. A stochastic component was introduced to reflect the uncertainty on the determination of missing data. Variables under study were: rainfall, air temperature, specific humidity, air pressure, wind speed, cloud cover, clear-sky longwave and shortwave radiation. Missing data were filled through regression methods, artificial neural networks, or by randomly selecting the missing variables from data classes presenting similar properties. The datasets showed an increase in temperature of over 1°C since the 1950s. They also maintained the diurnal and seasonal cycles for all variables, thus verifying their internal coherence. Uncertainty at the sub-daily scale did not propagate at longer time-scales for the climatic data. Finally, trends in the seasonal and diurnal cycle of main variables were analyzed and were found coherent with published data. As an illustration of a possible use of this dataset, variations in the water and energy budgets for 1950-2012 for a major ecosystem in the region were simulated using a detailed LSM/SVAT model (SiSPAT). This dataset could be used by the community to better understand and predict land-surface-atmosphere interactions in Central Sahel, including hydrological ones, such as historical changes in yield, growth of natural vegetation, changes in the water cycle and as a high-quality baseline for climate change impacts studies.

Floodplain grasslands have one of the highest productivities of non-cultivated ecosystems on Earth. They procure a wide variety of benefits to human beings. In Eastern Africa, grasslands of Echinochloa stagnina are primordial for pastoralists as highly productive dry-season grazing zones. Regular flooding is a critical property in maintaining their productivity and resulting services. Yet, construction of hydrologic infrastructure modifies the flooding regime of rivers and the consequences on downstream floodplain grasslands need to be assessed. This presentation focuses on quantifying the productivity of the floodplain grasslands in the Tana River Delta, Kenya, in order to assess potential changes under varying flooding regimes. The interactions between growth and floods are explored firstly at an experimental site, then through the construction of a process-based plant growth model adapted to floodplain grasslands. The 15-month experiment consisted in quantifying daily growth rates under various rainfall, irrigation, cutting and flooding regimes . Floods increased growth rates three-folds, and high productivities were maintained after the floods. The cutting regime and contribution of non-flood water also influenced productivity. Modelling allowed exploring the underlying processes explaining such behaviour. In an exploratory endeavour, the productivity of the grassland at the ecosystem scale was assessed with the model for a variety of flood and non-flooded scenarios. Decreasing floods led to a drop in annual productivity that could have serious consequences for the livestock keeping activities of the zone. This research highlights the importance of floods in the maintenance of high productivities for a floodplain grassland typical of East Africa, and maybe of the Sahelian band. The model, once further validated, could be used on other floodplain grasslands, such as those of the Niger delta. Results for the Tana River Delta would need to be discussed with the stakeholders so that proper action can be taken.

In the Sahel, the temperature is extremely high in Spring, with typical monthly-mean values of daily minimum, maximum and mean temperature of respectively 30, 40 and 35°C (Guichard et al. J. Hydrology 2009). Therefore, heat waves occurring at this period of the year can have particularly severe repercussions. Furthermore, current climate projections suggest that their frequency and intensity may increase in the future. Numerous heat-wave studies have focused on the mid-latitudes, but almost none on the Sahel. However, the specificities of the Sahelian climate imply that the mechanisms at play in this semi-arid region differ from those previously identified in the mid-latitudes. The influence of the Saharan Heat low is strong in this region; the soil is mostly dry in Spring, and soil-moisture feedbacks identified in mid-latitude studies are therefore unlikely to operate during Sahelian heat waves at this time of year. The present study is carried out within the ACASIS ANR project, which focuses on these Sahelian events. Here, we make use of complementary datasets (SYNOP and soundings data, high-frequency weather and flux stations, satellite data, meteorological reanalyses), together with models, to explore the importance of physical processes during a few selected heat-wave cases chosen from 2006 to 2014. These events are first identified with commonly-used indexes and the associated large-scale circulations are documented. The time-sequences of the surface energy budget and boundary layer diurnal and nocturnal states are then presented, with estimations of non-negligible cloud and aerosol effects on surface radiative fluxes. Our results imply in particular a major importance of the monsoon flow during the night, which induces dramatic changes in the surfaceatmosphere couplings, namely a sharp increase of the net longwave flux involving water vapour radiative properties, accompanied by a strong night-time warming. These processes are diversely captured by models and reanalyses.

En Afrique Sub-Saharienne, les zones humides forment d'importantes zones de pâturages pour bon nombre de pastoralistes. Le régime d'inondation de ces plaines influence leur fonctionnement et leur productivité. Pour comprendre et maitriser ces régimes, il est donc essentiel d'évaluer l'impact de l'infrastructure hydro-électrique sur les dynamiques d'inondations en aval des barrages. Pourtant, le manque de données disponibles, l'absence de modèles validés et la forte variabilité environnementale rendent cet exercice difficile. Cette thèse contribue à quantifier l'impact du changement des ressources hydriques sur la productivité fourragère des prairies inondables dans le Delta du fleuve Tana, au Kenya. 1/ Les caractéristiques de croissance et la productivité d'une prairie inondable à Echinochloa stagnina (Retz) P. Beauv. ont été déterminées pour différents régimes de fauche, d'irrigation et conditions d'inondations. Ensuite, un modèle de croissance adapté à des Graminées en C4, tropicales et pérennes, de prairies inondables a été développé. Il constitue, à notre connaissance, le premier modèle éco-physiologique adapté à ce type de prairies. 2/ Des processus hydrologiques importants pour le fonctionnement des écosystèmes (étendue, période, durée et fréquence d'inondation) ont été caractérisés grâce à un modèle de bilan hydrologique et à l'utilisation de techniques de télédétection, et cela en dépit de la faible instrumentalisation du bassin, du peu de données topographiques et d'un fort couvert nuageux. 3/ Une analyse préliminaire de l'impact de différents scénarios d'inondations sur la production fourragère a été effectuée en utilisant des indicateurs de services écosystémiques. Cette thèse participe à l'amélioration de nos connaissances des services écosystémiques des zones humides par la construction de modèles et par l'évaluation de scénarios dans une région du monde où ce type de données est rare.

Two Endangered primate taxa, the Tana River red colobus (population estimate less than 1200) and the Tana River mangabey (population estimate less than 2000), are only known from a restricted area of patchy riverine forest in the floodplain of the Lower Tana River in Kenya. This paper describes the discovery of several groups of both species further south, in the Tana Delta, which for the Tana River red colobus represents a marginal extension of its range, and for the Tana River mangabey a substantial extension of the known range. Both the extent and the quality of their previously known habitat continue to decline and the newly discovered sites are under severe threat from forest over-exploitation, attempts to redirect the river course away from the forest patches, expansion of large-scale irrigation both locally and upstream for food and for biofuel production which may affect river flows, and especially by the planned construction of a very large hydropower dam several hundred km upstream at Grand Falls. This sixth dam in the Tana River cascade may put an end to the natural flooding regime that has sustained the riverine forest where the primates reside. In fact, unless the new dam is designed and used to produce large managed flood releases that mimic the natural flooding regime, the entire high biodiversity floodplain and delta, its ecosystems, and the livelihoods dependent on them are in jeopardy. Locally, there is a need to come up with a common vision for the future of the delta and to implement proposed conservation measures.