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International audience; Due to global change, cities of the future will have to deal with more intense runoff and longer drought sequences, in addition to a growing urban and peri-urban population. French Mediterranean cities, such as Toulon, are already densely urbanised and exposed to the effects of global warming. The adaptation of their infrastructures is problematic. Cities with high development potential, such as Dakar, offer the opportunity to imagine other solutions for the management of water resources and its extremes in the context of global change. In particular, it is a question of managing the flows of water and substances linked to intense runoff events according to an ecohydrological logic that makes it possible to reduce environmental risks and increase social and economic benefits. To do this, we use a hydrologically-based geomatics model (IRIP) that produces predictive maps of areas of generation, transfer and accumulation of intense runoff and associated nutrients. This allows us to target effective intervention areas to reduce risks and increase water resources, for example by simulating land use change in appropriate locations and at the same time stimulating specific biological processes. The fundamental principle of ecohydrology is to balance energy flows with biological metabolic flows at the subcatchment scale. The mapping of intense runoff processes is a first step illustrated in this article for the cities of Toulon and Dakar. This first step is part of the Dakar'2030 project, which aims to rethink urban development and adapt it to climate change.; En raison du changement global, les villes du futur devront faire face à des ruissellements plus intenses et à des séquences de sécheresse plus longues, en plus d'une population urbaine et périurbaine croissante. Les villes méditerranéennes françaises, comme Toulon, sont déjà densément urbanisées et exposées aux effets du réchauffement climatique. L'adaptation de leurs infrastructures est problématique. Les villes à fort potentiel de développement, comme Dakar, offrent l'opportunité d'imaginer d'autres solutions pour la gestion des ressources en eau et de ses extrêmes dans le contexte du changement global. Il s'agit notamment de gérer les flux d'eau et de substances liés aux événements de ruissellement intenses selon une logique écohydrologique qui permet de réduire les risques environnementaux et d'augmenter les bénéfices sociaux et économiques. Pour ce faire, nous utilisons un modèle géomatique basé sur l'hydrologie (IRIP) qui produit des cartes prédictives des zones de génération, de transfert et d'accumulation du ruissellement intense et des nutriments associés. Cela nous permet de cibler des zones d'intervention efficaces pour réduire les risques et augmenter les ressources en eau, par exemple en simulant un changement d'utilisation des terres dans des endroits appropriés et en stimulant en même temps des processus biologiques spécifiques. Le principe fondamental de l'écohydrologie est d'équilibrer les flux d'énergie avec les flux métaboliques biologiques à l'échelle du sous-bassin versant. La cartographie des processus de ruissellement intense est une première étape illustrée dans cet article pour les villes de Toulon et de Dakar. Cette première étape s'inscrit dans le cadre du projet Dakar'2030, qui vise à repenser le développement urbain et à l'adapter au changement climatique.

International audience; Abstract Here, we simulate carbon dioxide (CO2) sequestration in 300 major world river basins (about 70% of global surface area) through carbonates dissolution and silicate hydrolysis. For each river basin, the daily timescale impacts under both the RCP 2.6 and RCP 8.5 climate scenarios were assessed relative to a historic baseline (1969-1999) using a cascade of models accounting for the hydrological evolution under climate change scenarios. Here we show that global temporal evolution of the CO2 uptake presents a general increase in the annual amount of CO2 consumed from 0.247 Pg C·y-1 to 0.261 and 0.273 Pg C·y-1, respectively for RCP 2.6 and RCP 8.5. Besides, despite showing a general increase for the global daily carbon sequestration, both climate scenarios present a decrease between June and August. Such projected changes have been mapped and evaluated against changes in hydrology, identifying hot spots and moments for the annual and seasonal periods.

International audience; The adaptation of semi-arid crops to climate changes is theoretically possible through agroforestry, provided that the trees exert little competition, or even increase the multifunctional LER (LER_M). We monitored microclimate, net primary productivity (NPP), CO2 and H2O fluxes in a semiarid agro-sylvo-pastoral system (Niakhar, Senegal), dominated by the multipurpose Faidherbia albida (FA) tree. Undercrops were mainly millet and peanut, under annual rotation. We scanned a 1.24 ha millet under FA plot with UAV photogrammetry in RGB, thermal infrared and multispectral bands. At harvest, we collected 12 subplots of 15 millet holes each, distributed either below the crown of FA, or at 2.5 x crown radius, or at 5 x crown radius. We separated all organs. The whole millet root system (0-200 cm) was sampled also in 2 m trenches, totalizing 4 millet holes, where all roots were sorted by layer. The whole plot harvest will allow extrapolating yield from subplots, through UAV images. Millet yield per unit ground area was about 3 times higher below FA, with still a positive influence at 2.5 x crown radius and less impacts of pests close to FA. In the trenches, we noted higher soil humidity and SOC close to the FA trunks. This observatory is open for collaboration.

National audience; The Ubangui River in Bangui comes from The Mbomu River, the CAR side and the Uele River from the DRC. Its flow till Bangui in the bottom has 546 kilometers long and has numerous anastomoses, sprinkled with a good deal of islands and strangulations (Palambo and Bangui). Its side basin is influenced by the Sudano-Guinean variable of dumb tropical climate. This paper revisits the hydroclimatic changes of the Ubangui River at the outlet of Bangui in favor of a new hydropluviometric serial data from 1935 to 2015. The annual rainfall and hydrological data series were analyzed using different statistical tests (rainfall index and flow index, breaks research, depletion coefficients). Rainfall series still shows only one break in 1970, which confirms the exceptionality of this climate disruption in Central Africa. However hydrological series identifies four different hydrological periods: 1935-1959, 1960-1970, 1971-1982 and 1982-2013. The last period shows an average deficit of -22% (2 893 m(3)/s) compared to the mean annual flow over the entire study period (3 700 m(3)/s). The average relationship rain/runoff did not change during these well-identified hydroclimatic periods, suggesting that the hydrological functioning of the Ubangui River has not changed because of this climate disruption. It is attributed to the low human impact over this basin and to the small change of the vegetation cover. However the comparison of annual changes in the depletion coefficient with the volume mobilized by the aquifer flows to sustain the Ubangui River flows clearly indicates the relationship change before and after 1970 and after 2000.; Ce papier revisite l'évolution hydroclimatique de l'Oubangui à Bangui à la faveur d'une nouvelle série hydropluviométrique de 1935 à 2015. Pour cela, les données annuelles pluviométriques et hydrologiques de l'Oubangui à Bangui ont été analysées avec différents tests statistiques (indices pluviométrique et d'écoulement, recherches de ruptures, coefficients de tarissement). La série pluviométrique n'indique toujours qu'une seule cassure en 1970, ce qui confirme l'exceptionnalité de cette rupture climatique en Afrique Centrale. Par contre, la série hydrologique permet d'identifier quatre périodes hydrologiques différentes : 1935-1959, 1960-1970, 1971-1982 et 1982-2013. La dernière période montre un déficit moyen de -22 % (2 893 m3/s) par rapport au débit moyen annuel sur toute la période étudiée (3 700 m3/s.). Les relations moyennes pluie/débit n'ont pas évolué au cours de ces périodes hydroclimatiques, semblant indiquer que le fonctionnement hydrologique de l'Oubangui n'a pas changé du fait de la rupture climatique de 1970. Cela est attribué à la faible anthropisation de ce bassin et la faible évolution de son couvert végétal. Cependant la comparaison de l'évolution annelle du coefficient de tarissement avec le volume mobilisé par l'aquifère pour soutenir les écoulements de l'Oubangui indique clairement un changement de contribution de la nappe avant et après 1970, puis après 2000.

International audience; This paper discusses the design of an incentive based framework for the promotion and possible upscaling of a biogas-based pilot scheme to manage soil fertility and erosion control on sloping lands, with a focus on policy implications. The study is based on research conducted in 2007 within a small agricultural village of the Hoa Binh Province in Northern Vietnam.

The challenges facing sustainable land and water in the future are not founded on lack of technological tools or interventions that are at the disposal of managers. There are clear impediments to adoption of these practices that will require innovative ways of knowledge dissemination, carefully crafted policies, incentives and commitment from governments and agencies charged with the management of land and water resources. In addition, there will be a need to create desirable innovative productive agro-ecosystems that maintain and enhance a range of ecosystem services and that attract the will of each farmer. In many cases, this can best be achieved by mimicking aspects of natural systems (LeFroy et al 1999), for example: • Paddy fields mimic the water retention of natural wetlands to provide multiple benefits including rice and fish production, flood mitigation, ground water recharge, soil erosion control, water purification; • Plantations can mimic natural forests, with well developed understorey to prevent soil erosion, provide habitat and promote biodiversity.

International audience; Based on two case studies conducted at local sites in Northern Thailand and Lao PDR, the objectives of this paper are (i) to assess whether conditions for the establishment of PES at the watershed level exist in the uplands of mainland SE Asia and (ii) to examine and discuss limitations that are likely to impinge on direct transfer of the PES concept as well as the institutional adaptations and support that are required for the successful implementation of PES markets in this regional context. The study's main findings are that: (i) acceptance of PES principles and constraints are directly related to stakeholders' perception of their land rights irrespective of their actual rights; (ii) willingness to pay (WTP) is very low among local stakeholders, making any PES market unlikely to emerge without external support; (iii) the classical scheme for watershed services hardly applies in its original form because environmental service (ES) providers and buyers are generally the same people; (iv) where potential ES buyers feel that ES providers are better-off or wealthier than them, they do not have any WTP for ES; (v) good governance, including a strong liaising at various levels between people and the authorities is a strong prerequisite for the successful establishment of PES markets, even without direct government funding.

projet Gihrex

This report identifies the driving forces for reforestation in three villages of Northern Vietnam. Using an institutional analysis focused on the rules governing upland access and use, the authors assess the relative impact of state policies (reforestation programs and forestland allocation) on land use change. Findings show that the latter are indirectly responsible for reforestation, but not because of the incentives they provided. Instead, they disrupted the local rules governing annual crop cultivation and grazing activities leading to the end of annual cropping. Tree plantation was chosen by farmers as a last resort option. Lessons learned highlight the importance of local level studies and collective rules for land management.

International audience

Station 1: Soil erosion and land management focused research; International audience; This poster studies the impact of land-use change on soil loss from sloping lands, presenting research on biophysical processes and their environmental and economic consequences. Farming systems are also analysed to infer the driving forces behind farmer strategies and practices. The Vietnam MSEC research program works in a small agricultural experimental watershed of around 50 ha, northeast of Hanoi. The cultivated steep slopes have been equipped to assess water discharge and sediment loads. Soil erosion here has negative impacts on upstream and downstream communi-ties. Increased sediment from these catchments reflects a loss of the fertile topsoil that farmers depend upon. In addition, increased sediment loads in streams and rivers have a negative impact on water quality and the longevity of water storage structures, both of which have significant economic and environmental implications.

In spite of the green revolution of the 1990s, guaranteeing food security remains a challenge in large parts of the mountains of Southeast Asia. It is largely accepted that the most suitable farming systems for the uplands are based either on tree crops or mixed crop-livestock systems, both to manage the soil fertility and to maintain the soil in place. How can this be applied for a sustainable farming system? This project, from the DURAS international program to promote sustainable development in agricultural systems, aims to develop and enhance sustainable agriculture that makes the best use of: 1) the local knowledge and skills of farmers; 2) social capital - people's capacities to work together to solve common management problems; 3) nature's goods and services; and 4) public goods - rural jobs, clean water, flood protection, landscape quality, etc. More specifically, the Vietnamese part of this project works specifically on a better understanding of local-knowledge implications from the disadvantaged communities living in mountainous areas through the spontaneous innovations of farming systems. Local participation has been strengthened along the research and extension processes by a case study: the introduction of fodder crop in the farming system. After completion and evaluation of the first round of fodder tests within experimental plots, on-farm tests have been conducted under farmer management for the most promising species. The farmers selected the fodder species (temperate and/or tropical), the planting place (upland and/or lowland) and the surface on which to cultivate. Interactions with farmers and local extension officers were initiated at the very onset of the project through a former project on watershed management (MSEC program). In addition, experiments and surveys of fodder crops (yield, harvesting and forage management, agricultural calendar etc.) were conducted in close cooperation with farmers in their own fields. Dissemination of the results of these two activities have after one year been greatly facilitated, not only at the village level but also at the commune level. Thus, it seems that methodologies tested and developed by the project will contribute to an improvement of extension approaches for extension workers and local managers as well as to a better linkage between researchers, development agents and farmers. On the other hand, the project is also carrying out experiments on soil and water quality to improve water and soil fertility management at the watershed level, as well as an assessment of the productivity and nutritional value of tested fodder species and their seed production capacity in Southeast Asian mountain conditions. Based on knowledge gained during farmer meetings and experience from the experimental fields, farmers have already defined their strategy. They cultivate only tropical species in the uplands and temperate species in the lowlands, in keeping with scientific knowledge. During the first year, 2006, around 4 ha of forage have been planted; next year more than 20 ha will be planted with fodder. So, by involving village groups as participants, all arguments are mobilized for the successful identification, definition and extension of new agricultural practices for husbandry integration. Furthermore, effective dissemination can be expected in the future.

Through the lens of the Institutional Analysis and Development (IAD) framework, the paper analyses how the combination of reforestation programs and households uplands allocation has significantly altered land management in a commune of Northern Vietnam. "It is based on a three villages' case study where has traditionally been living the ethnic Muong minority. Due to government policies, land management has dramatically shifted from forested land community-based management and shifting cultivation practices to private land management. In a first stage, land-use has evolved from annual cropping to secondary forest plantation and fallow. Furthermore, the collapse of common areas has led to conflicts for grazing land and fuel wood. Very recently, urbanization and a liberalization of market economy have resulted in further changes both in land management and in land-use. "We argue that the government policies implemented in the end of the 1990s have not only impacted on individual farmer land-use, but has also induced the collapse of existing informal institutional arrangements governing uplands management. In turn this has had repercussions on farmers' strategies and households' resilience. For instance, important changes in land access and land-use rights broke up the subtle collective rules that enabled grazing and cropping systems co- existence. "Further to the analysis of policies' impacts on land use and farmers livelihoods, this study presents how, and under what conditions for a three decade period, farmers have been able to adopt new strategies, new land management systems and new institutional arrangements. "Finally, we make recommendations for decision-making: on the one hand, directions for new policies development and on the other, advice to champion policies which match impacts to pursued objectives. "We adopt a political ecology perspective by focusing on institutions and policies as driving forces for environmental change, and propose a comprehensive approach for analyzing change in land management in mountainous areas. Methodology for data analysis combines the use of the IAD, a rigorous institutional framework that has been widely used in the field of the commons studies, with an historical perspective. The approach integrates environmental, social, and economic factors - from the micro to the macro level - to explain how uniform national policies have lead to different farmers' strategies and distinct upland management systems

Through the lens of the Institutional Analysis and Development (IAD) framework, the paper analyses how the combination of reforestation programs and households uplands allocation has significantly altered land management in a commune of Northern Vietnam. Based on a three villages’ case study, we argue that the government policies implemented in the end of the 1990s have not only impacted on individual farmer land-use, but has also induced the collapse of existing informal institutional arrangements governing uplands management. In turn this has had repercussions on farmers’ strategies and households’ resilience. For instance, important changes in land access and land-use rights broke up the subtle collective rules that enabled grazing and cropping systems co-existence. Further to the analysis of policies’ impacts on land use and farmers livelihoods, this study examines how, and under what conditions for a three decade period, farmers have been able to adopt new strategies, new land management systems and new institutional arrangements. Furthermore, we make recommendations for policy-making: on the one hand, directions for new policies development and on the other, advice to champion policies which match impacts to pursued objectives. We adopt a political ecology perspective by focusing on institutions and policies as driving forces for environmental change, and propose a comprehensive approach for analyzing land-use change in mountainous areas. Methodology for data analysis combines the use of the IAD, a rigorous institutional framework that has been widely used in the field of the commons studies, with an historical perspective. The approach integrates environmental, social, and economic factors – from the micro to the macro level – to explain how uniform national policies have lead to different farmers’ strategies and distinct upland management systems.

International audience; The Congo (Zaire) River, the world's second largest river in terms both of water discharges and of drainage area after the Amazon River, has remained to date in a near-pristine state. For a period between 2 and 6 years, the mainstream near the river mouth (Brazzaville/Kinshasa station) and some of the major and minor tributaries (the Oubangui, Mpoko, and Ngoko-Sangha) were monitored every month for total suspended sediment (TSS), particulate organic carbon (POC), and dissolved organic carbon (DOC). In this large but relatively flat equatorial basin, TSS levels are very low and organic carbon is essentially exported as DOC: from 74% of TOC for the tributaries flowing in savannah regions and 86% for those flowing in the rain forest. The seasonal patterns of TSS, POC, and DOC show clockwise hysteresis in relation to river discharges, with maximum levels recorded 2 to 4 months before peak flows. At the Kinshasa/Brazzaville station, the DOC distribution is largely influenced by the input from the tributaries draining the large marshy forest area located in the center of the basin. There is a marked difference between specific fluxes, threefold higher in the forest basins than in the savannah basins. The computation of inputs to the Atlantic Ocean demonstrates that the Congo is responsible for 14.4 × 106 t/yr of TOC of which 12.4 × 106 t/yr is DOC and 2 × 106 t/yr is POC. The three biggest tropical rivers (the Amazon, the Congo, and the Orinoco), with only 10% of the exoreic world area drained to world oceans, contribute ~4% of its TSS inputs but 15-18% of its organic carbon inputs. These proportions may double when considering only world rivers discharging into the open ocean.

International audience; ln 1998 and 1999, runoff and soil erosion were monitored on runoff plots in Southern Mali. Seven runoff plots were set up on three different soils (Alfisol, Vertisol, and Lithosol), with three land uses, i.e. old natural bush fallow, cropping with conventional tillage (maize then cotton), and cropping with minimum tillage on the seed line. Soil samples were collected at 0-10 cm in order to determine soil carbon content, aggregate stability (to wet-sieving after fast wetting) and clod stability to waterdrops. The results indicated that low clay (and fine silt) contents and intensive tillage resulted in low soil carbon content and weak aggregate and clod stability, and high runoff and erosion. Thus runoff and erosion tended to be lower on the (clayey) Vertisol and under fallow than on the Alfisol and under conventional tillage. The results were more complex with minimum tillage (as compared with other land uses, runoff and erosion were higher when annual rainfall was high, but the opposite occurred in rather dry years) and on the Lithosol (high runoff but limited erosion due to the high topsoil content in gravels). Runoff correlated with topsoil aggregate stability (which in turn correlated with clay and carbon contents), and erosion with clod stability (which in turn correlated with fine root contents). Thus land uses that promoted the stability of the topsoil structure (e.g. organic return to the soil including root biomass, reduced tillage) decreased soil susceptibility to runoff and erosion. Furthermore, these results confirmed and extended the validity of simple erodibility tests (aggregate and clod stability) for the assessment of runoff and interrill erosion at field scale. The clod stability test seemed to better explain erosion risks than the aggregate stability test, as it takes the stabilizing action of the roots into account. Additionally, the clod test requires few laboratory devices. However, it can take long when clods are stable (10 s to 120 min for each clod), and it requires larger soil samples that must be transported carefully.; En 1998 et 1999, le ruissellement et l'érosion ont été mesurés au Sud-Mali sur sept parcelles d'érosion standard (100 m²) sous pluies naturelles. Ces parcelles étaient installées sur sol ferrugineux tropical, sol brun vertique et sol peu évolué d'érosion, avec les modes d'occupation suivants : jachère arbustive, culture avec labour (maïs puis coton, en culture attelée), culture avec travail minimum (maïs puis coton, travail à la pioche sur le rang seulement). Des échantillons de sol ont été prélevés à 0-10 cm de profondeur, afin de déterminer notamment la teneur en carbone, la stabilité des agrégats (tamisage dans l'eau) et la stabilité des mottes (sous l'impact de gouttes d'eau). Les résultats montrent que lorsque le taux d'argile (et limons fins) est faible et les pratiques culturales intensives, la teneur en carbone du sol et la stabilité des agrégats et des mottes sont faibles également, tandis que le ruissellement et l'érosion sont élevés. De manière générale, le sol brun vertique (argileux) et les sols sous jachère sont donc moins sensibles au ruissellement et à l'érosion que le sol ferrugineux et les sols labourés. Les résultats sont plus complexes en cas de travail minimum (par rapport aux autres traitements, ruissellement et érosion sont importants en année humide mais faibles en année sèche) et sur sol peu évolué (ruissellement élevé mais érosion limitée, du fait de la richesse en éléments grossiers en surface). Les résultats montrent également que le ruissellement est lié à la stabilité des agrégats (elle-même liée à la teneur en argile et en carbone), et que l'érosion est fonction de la stabilité des mottes (elle-même fonction de la richesse en radicelles). Les pratiques qui garantissent une stabilité élevée de la couche de sol superficiel permettent donc de diminuer la sensibilité du sol au ruissellement et à l'érosion. Par ailleurs, ces résultats confirment et étendent la validité de tests d'érodibilité simples (stabilité des agrégats et des mottes) pour évaluer le ruissellement et l'érosion à l'échelle parcellaire. Le test de stabilité des mottes peut être long quand les mottes sont stables (de 10 s à 120 min). De plus, il exige une quantité de sol plus importante (120 g) que le test de stabilité des agrégats (20 g) et un transport précautionneux des mottes jusqu'au laboratoire. En revanche, il requiert très peu de matériel de laboratoire (pipette).