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The Agricultural Model Intercomparison and Improvement Project (AgMIP) is a major international effort linking the climate, crop, and economic modeling communities with cutting-edge information technology to produce improved crop and economic models and the next generation of climate impact projections for the agricultural sector. The goals of AgMIP are to improve substantially the characterization of world food security due to climate change and to enhance adaptation capacity in both developing and developed countries. Analyses of the agricultural impacts of climate variability and change require a transdisciplinary effort to consistently link state-of-the-art climate scenarios to crop and economic models. Crop model outputs are aggregated as inputs to regional and global economic models to determine regional vulnerabilities, changes in comparative advantage, price effects, and potential adaptation strategies in the agricultural sector. Climate, Crop Modeling, Economics, and Information Technology Team Protocols are presented to guide coordinated climate, crop modeling, economics, and information technology research activities around the world, along with AgMIP Cross-Cutting Themes that address uncertainty, aggregation and scaling, and the development of Representative Agricultural Pathways (RAPs) to enable testing of climate change adaptations in the context of other regional and global trends. The organization of research activities by geographic region and specific crops is described, along with project milestones. Pilot results demonstrate AgMIP's role in assessing climate impacts with explicit representation of uncertainties in climate scenarios and simulations using crop and economic models. An intercomparison of wheat model simulations near Obregón, Mexico reveals inter-model differences in yield sensitivity to [CO2] with model uncertainty holding approximately steady as concentrations rise, while uncertainty related to choice of crop model increases with rising temperatures. Wheat model simulations with mid-century climate scenarios project a slight decline in absolute yields that is more sensitive to selection of crop model than to global climate model, emissions scenario, or climate scenario downscaling method. A comparison of regional and national-scale economic simulations finds a large sensitivity of projected yield changes to the simulations’ resolved scales. Finally, a global economic model intercomparison example demonstrates that improvements in the understanding of agriculture futures arise from integration of the range of uncertainty in crop, climate, and economic modeling results in multi-model assessments.

The Agricultural Model Intercomparison and Improvement Project (AgMIP) is a major international effort linking the climate, crop, and economic modeling communities with cutting-edge information technology to produce improved crop and economic models and the next generation of climate impact projections for the agricultural sector. The goals of AgMIP are to improve substantially the characterization of world food security due to climate change and to enhance adaptation capacity in both developing and developed countries. Analyses of the agricultural impacts of climate variability and change require a transdisciplinary effort to consistently link state-of-the-art climate scenarios to crop and economic models. Crop model outputs are aggregated as inputs to regional and global economic models to determine regional vulnerabilities, changes in comparative advantage, price effects, and potential adaptation strategies in the agricultural sector. Climate, Crop Modeling, Economics, and Information Technology Team Protocols are presented to guide coordinated climate, crop modeling, economics, and information technology research activities around the world, along with AgMIP Cross-Cutting Themes that address uncertainty, aggregation and scaling, and the development of Representative Agricultural Pathways (RAPs) to enable testing of climate change adaptations in the context of other regional and global trends. The organization of research activities by geographic region and specific crops is described, along with project milestones. Pilot results demonstrate AgMIP's role in assessing climate impacts with explicit representation of uncertainties in climate scenarios and simulations using crop and economic models. An intercomparison of wheat model simulations near Obregón, Mexico reveals inter-model differences in yield sensitivity to [CO2] with model uncertainty holding approximately steady as concentrations rise, while uncertainty related to choice of crop model increases with rising temperatures. Wheat model simulations with mid-century climate scenarios project a slight decline in absolute yields that is more sensitive to selection of crop model than to global climate model, emissions scenario, or climate scenario downscaling method. A comparison of regional and national-scale economic simulations finds a large sensitivity of projected yield changes to the simulations’ resolved scales. Finally, a global economic model intercomparison example demonstrates that improvements in the understanding of agriculture futures arise from integration of the range of uncertainty in crop, climate, and economic modeling results in multi-model assessments.

The vast majority of land users at the Central Plateau of Burkina Faso make a living by farming small plots, where mainly staple crops are produced for subsistence use. Both area interventions and line interventions comprising indigenous techniques as well as introduced techniques can be encountered at the Central Plateau and have proved to be effective. There is a preference for semi-permeable line measures that slow down runoff and prevent water logging in wet periods.In order to ascertain the rationale behind the choice of soil and water conservation measures and the implementation strategy, five large soil and water conservation projects in three Sahelian countries have been investigated. The choice of technology and the way of implementation differed greatly between projects. This was attributable more to the preference of donors and projects than to any physical, socio-economic and agronomic differences. On the basis of project performances, a recommendable strategy for farmers' fields appeared to be the use of the local zay technique to achieve a short-term improvement, and to combine this with stone lines or vegetation barriers for a long-term effect.Low adoption rate of soil and water conservation (SWC) measures in erosion-prone areas is often ascribed to the high investment costs of measures. The costs of these measures may seem modest in comparison to costs for infrastructure, but they are often too high for the individual subsistence farmer, especially in marginal semi-arid zones in the Sahel. Investment costs are highest for stone rows, whereby the transport of stones requires substantial inputs of labour and means of transport. Vegetation barriers are less costly, but have the disadvantage that they need to be planted in the rainy season, when agricultural production activities have the highest priority.A major reason why farmers consider the costs prohibitive relates to the uncertain nature of the benefits. These benefits comprise of several elements, some of which may have immediate effect (e.g. moisture retention), but most of which occur only gradually over a long period of time, and are hard to assess and even harder to quantify. In a qualitative multi-criteria analysis stone rows showed the best results, and this was also the measure that with the help of development projects, has been most often applied at the Central Plateau in Burkina Faso. However, vegetation barriers, which have not yet been greatly promoted come a close second and are the best solution in areas where stones are scarce or not available. This conclusion was the starting point of the water conservation research by means of vegetation barriers.The on station field experiment was set up to evaluate the effectiveness of vegetation barriers for soil and water conservation under semi-arid conditions at the research station of the Institute de Développement Rural (IDR) at Gampela.Seven local plant species (grasses: Andropogon gayanus, Vetiveria zizanioides ; woody species: Acacia nilotica, Guiera sengalensis,Piliostigma reticulatum, Ziziphus mauritiana ; and a succulent: Agave sisalana ) were planted on a 2 % slope of a sandy loam (Chromic Luvisol), in 21 plots of 20 x 20 m as conservation barriers, along the contour.To determine the runoff interception efficiency of barriers and to find out the influence of slope length and alley treatment, runoff induced by a large number of storms was measured on plots with slope lengths of 1.25 m (1 m 2), 6.25 m (5 m 2), and 12.5 m (10 m 2). Plots without a barrier (no barrier) were used as the control. Grass barriers and stone rows proved to be very effective (effective barrier) in impeding runoff and reducing runoff to only 20 % of precipitation. The runoff through woody species and succulents (less effective barrier) was about 50 % of precipitation. By comparison with the control, a barrier always resulted in water conservation. Less effective barriers with a bare or cropped alley showed a decrease in runoff percentage with an increase of plot length along the slope, whereas effective barriers with a bare or cropped alley showed an increase of runoff along the slope. The effect of crop development on runoff was rather small. Runoff reduction during the growing season was highest on plots without a barrier and on plots with the less effective barriers.On short (1.25 m) and long (12.5 m) slopes the influence of rain intensity on runoff production was marginal. On the medium slope length (6.25 m), rain intensity influenced runoff most on plots with a less effective barrier. A general conclusion was that for longer slopes, all factors such as type of barrier, land use and rain intensity became less important. In that situation, large runoff volumes exceeded the quantity of water that can be dammed by the vegetation barriers, and can be intercepted as a result of land use activities and vegetation on the alley. It is concluded that barriers improve water conservation and are most effective when closely spaced.Large differences in sediment transport in the amount of sediment yield were found between the barrier types. Grasses and natural vegetation proved to be very effective in catching soil particles and diminishing sediment transport. The dense effective barriers slow down flow velocity, build up backwater and promote sedimentation upstream. The through flow in the less effective barriers with woody species and succulents was slightly hampered and flow velocity was not reduced enough, resulting in a higher sediment transport. Under degraded conditions soil loss diminished 50 % with less effective and 70-90 % with effective barriers. During the initial cropping phase (light tillage) sediment transport was reduced 40-60 % with effective barriers and showed an increase with less effective barriers. In the full tillage (weeding) period sediment transport decreased by 80-90 % for effective and 70 % for less effective barriers. Sediment yield could be best predicted by the erosivity index, second best by runoff amount (mm) closely followed by maximum peak intensity. All these parameters were related to the volume of overland flow needed to transport soil particles.At the research site annual rain quantities seldom gave rise to a shortage of water for vegetation barriers and sorghum. Conversely, dry spells had a big influence on soil water, exhausting it sometimes during the growing season, and causing delay in plant growth. Water loss by evaporation was negligible under (effective) Andropogon and substantial under (less effective) Ziziphus barriers. Reduced evaporation and the larger effect on runoff reduction compensated the high transpiration of Andropogon. Most barriers transpired without restrictions, when water was readily available. Only Piliostigma showed to limit transpiration during the second part of the growing season.The soil water content was monitored twice a week at different measuring depths with the TDR technique at a transect perpendicular to the barriers. For the investigated alley crop system it was found that, despite the difference in effectiveness of the barriers and soil water dynamics, there were no striking differences in yield (grain and straw) between the treatments in the distinct years. However, there were big differences in crop yields between the respective years. These differences were strongly related to the amount and the distribution of the rain over the crop development stages. When water for the sorghum crop was not always readily available during the growing season, but when rain distribution and rain quantity were favourable (1999), yields were close to average on-station yields. In the dry year 1998, there was a total annual amount of rain to produce maximum yields, but a number of dry spells had a big influence. In 1998, about half of the annual water and in 1999, only about a third of the available annual water was used for crop production.Effective barriers conserved water even during dry years and compensated at least their own consumption and increased crop yields over a distance of about 6 m upstream of the barrier. Since the soil water was always enhanced close to and under the effective (Andropogon) barrier and yields did not reflect to favourable soil water conditions, ponding and shading appeared to be important growth constraints. The barrier effect of less effective Ziziphus barriers was not good during dry years and even not enough to compensate its own consumption. In dry years, water competition was responsible for yield reductions adjacent to the barrier on the less effective barrier plots. In wet years this barrier caught enough water for its own water consumption and also enough to improve crop yields a few meters upstream. Stone row barriers sometimes retained too much runoff water causing water logging. Even in dry years the barrier effect of stone rows was less good than the effective vegetation barrier. Effective vegetation barriers were slightly better than stone rows, but the difference remained small.Management actions have to be undertaken to diminish the negative impacts, like ponding or excessive water use by the barriers. During drought the barrier has to be cut back to diminish competition. During wetness, removal of some stones in the stone row and cutting a part of the effective vegetation barrier can help to drain excess water. In farmers fields it was often observed that only short rows of Andropogon were applied. Obviously their experience is that in case of drought these short barriers catch enough water and in case of abundance, the water can flow round.Runoff management is one of the tools to increase the available water for agricultural production in areas where rainfall is erratic. From the Gampela research runoff percentages can be estimated for design purposes. Water use of vegetation barriers was related to meteorological factors and soil moisture availability and found to be simple and reliable to predict transpiration.Amongst the soil and water conservation (SWC) measures adopted in the Sahel, contour vegetation barriers (CVB) constitute a cheap option in terms of labour and material requirements. In order to understand the actual adoption and maintenance of CVB, labour requirements of commonly adopted CVB species were evaluated. Labour requirements for the installation of 100 m CVB varied from 7-8 man-days when using cuttings or direct sowing to 15 man-days when installed from nursery seedlings, excluding 8 days for the installation of a dead fence. Maintenance takes 2-4 days per 100m. Phasing the installation over several years is an option to overcome labour constraints. Low labour requirements for establishment and management do not explain the rather low adoption and poor maintenance of vegetation barriers. The labour requirement for establishment of barriers at the beginning of the growing season is not a real constraint. Farmers mostly choose CVB species and planting methods with low labour requirements and prefer species with additional benefits such as thatching grass, oil for soap making and fodder and fruits.At the Central Plateau vegetation barriers can play a vital role in conserving soil and water. Well managed vegetation barriers can contribute to the re-greening of the area.

The vast majority of land users at the Central Plateau of Burkina Faso make a living by farming small plots, where mainly staple crops are produced for subsistence use. Both area interventions and line interventions comprising indigenous techniques as well as introduced techniques can be encountered at the Central Plateau and have proved to be effective. There is a preference for semi-permeable line measures that slow down runoff and prevent water logging in wet periods.In order to ascertain the rationale behind the choice of soil and water conservation measures and the implementation strategy, five large soil and water conservation projects in three Sahelian countries have been investigated. The choice of technology and the way of implementation differed greatly between projects. This was attributable more to the preference of donors and projects than to any physical, socio-economic and agronomic differences. On the basis of project performances, a recommendable strategy for farmers' fields appeared to be the use of the local zay technique to achieve a short-term improvement, and to combine this with stone lines or vegetation barriers for a long-term effect.Low adoption rate of soil and water conservation (SWC) measures in erosion-prone areas is often ascribed to the high investment costs of measures. The costs of these measures may seem modest in comparison to costs for infrastructure, but they are often too high for the individual subsistence farmer, especially in marginal semi-arid zones in the Sahel. Investment costs are highest for stone rows, whereby the transport of stones requires substantial inputs of labour and means of transport. Vegetation barriers are less costly, but have the disadvantage that they need to be planted in the rainy season, when agricultural production activities have the highest priority.A major reason why farmers consider the costs prohibitive relates to the uncertain nature of the benefits. These benefits comprise of several elements, some of which may have immediate effect (e.g. moisture retention), but most of which occur only gradually over a long period of time, and are hard to assess and even harder to quantify. In a qualitative multi-criteria analysis stone rows showed the best results, and this was also the measure that with the help of development projects, has been most often applied at the Central Plateau in Burkina Faso. However, vegetation barriers, which have not yet been greatly promoted come a close second and are the best solution in areas where stones are scarce or not available. This conclusion was the starting point of the water conservation research by means of vegetation barriers.The on station field experiment was set up to evaluate the effectiveness of vegetation barriers for soil and water conservation under semi-arid conditions at the research station of the Institute de Développement Rural (IDR) at Gampela.Seven local plant species (grasses: Andropogon gayanus, Vetiveria zizanioides ; woody species: Acacia nilotica, Guiera sengalensis,Piliostigma reticulatum, Ziziphus mauritiana ; and a succulent: Agave sisalana ) were planted on a 2 % slope of a sandy loam (Chromic Luvisol), in 21 plots of 20 x 20 m as conservation barriers, along the contour.To determine the runoff interception efficiency of barriers and to find out the influence of slope length and alley treatment, runoff induced by a large number of storms was measured on plots with slope lengths of 1.25 m (1 m 2), 6.25 m (5 m 2), and 12.5 m (10 m 2). Plots without a barrier (no barrier) were used as the control. Grass barriers and stone rows proved to be very effective (effective barrier) in impeding runoff and reducing runoff to only 20 % of precipitation. The runoff through woody species and succulents (less effective barrier) was about 50 % of precipitation. By comparison with the control, a barrier always resulted in water conservation. Less effective barriers with a bare or cropped alley showed a decrease in runoff percentage with an increase of plot length along the slope, whereas effective barriers with a bare or cropped alley showed an increase of runoff along the slope. The effect of crop development on runoff was rather small. Runoff reduction during the growing season was highest on plots without a barrier and on plots with the less effective barriers.On short (1.25 m) and long (12.5 m) slopes the influence of rain intensity on runoff production was marginal. On the medium slope length (6.25 m), rain intensity influenced runoff most on plots with a less effective barrier. A general conclusion was that for longer slopes, all factors such as type of barrier, land use and rain intensity became less important. In that situation, large runoff volumes exceeded the quantity of water that can be dammed by the vegetation barriers, and can be intercepted as a result of land use activities and vegetation on the alley. It is concluded that barriers improve water conservation and are most effective when closely spaced.Large differences in sediment transport in the amount of sediment yield were found between the barrier types. Grasses and natural vegetation proved to be very effective in catching soil particles and diminishing sediment transport. The dense effective barriers slow down flow velocity, build up backwater and promote sedimentation upstream. The through flow in the less effective barriers with woody species and succulents was slightly hampered and flow velocity was not reduced enough, resulting in a higher sediment transport. Under degraded conditions soil loss diminished 50 % with less effective and 70-90 % with effective barriers. During the initial cropping phase (light tillage) sediment transport was reduced 40-60 % with effective barriers and showed an increase with less effective barriers. In the full tillage (weeding) period sediment transport decreased by 80-90 % for effective and 70 % for less effective barriers. Sediment yield could be best predicted by the erosivity index, second best by runoff amount (mm) closely followed by maximum peak intensity. All these parameters were related to the volume of overland flow needed to transport soil particles.At the research site annual rain quantities seldom gave rise to a shortage of water for vegetation barriers and sorghum. Conversely, dry spells had a big influence on soil water, exhausting it sometimes during the growing season, and causing delay in plant growth. Water loss by evaporation was negligible under (effective) Andropogon and substantial under (less effective) Ziziphus barriers. Reduced evaporation and the larger effect on runoff reduction compensated the high transpiration of Andropogon. Most barriers transpired without restrictions, when water was readily available. Only Piliostigma showed to limit transpiration during the second part of the growing season.The soil water content was monitored twice a week at different measuring depths with the TDR technique at a transect perpendicular to the barriers. For the investigated alley crop system it was found that, despite the difference in effectiveness of the barriers and soil water dynamics, there were no striking differences in yield (grain and straw) between the treatments in the distinct years. However, there were big differences in crop yields between the respective years. These differences were strongly related to the amount and the distribution of the rain over the crop development stages. When water for the sorghum crop was not always readily available during the growing season, but when rain distribution and rain quantity were favourable (1999), yields were close to average on-station yields. In the dry year 1998, there was a total annual amount of rain to produce maximum yields, but a number of dry spells had a big influence. In 1998, about half of the annual water and in 1999, only about a third of the available annual water was used for crop production.Effective barriers conserved water even during dry years and compensated at least their own consumption and increased crop yields over a distance of about 6 m upstream of the barrier. Since the soil water was always enhanced close to and under the effective (Andropogon) barrier and yields did not reflect to favourable soil water conditions, ponding and shading appeared to be important growth constraints. The barrier effect of less effective Ziziphus barriers was not good during dry years and even not enough to compensate its own consumption. In dry years, water competition was responsible for yield reductions adjacent to the barrier on the less effective barrier plots. In wet years this barrier caught enough water for its own water consumption and also enough to improve crop yields a few meters upstream. Stone row barriers sometimes retained too much runoff water causing water logging. Even in dry years the barrier effect of stone rows was less good than the effective vegetation barrier. Effective vegetation barriers were slightly better than stone rows, but the difference remained small.Management actions have to be undertaken to diminish the negative impacts, like ponding or excessive water use by the barriers. During drought the barrier has to be cut back to diminish competition. During wetness, removal of some stones in the stone row and cutting a part of the effective vegetation barrier can help to drain excess water. In farmers fields it was often observed that only short rows of Andropogon were applied. Obviously their experience is that in case of drought these short barriers catch enough water and in case of abundance, the water can flow round.Runoff management is one of the tools to increase the available water for agricultural production in areas where rainfall is erratic. From the Gampela research runoff percentages can be estimated for design purposes. Water use of vegetation barriers was related to meteorological factors and soil moisture availability and found to be simple and reliable to predict transpiration.Amongst the soil and water conservation (SWC) measures adopted in the Sahel, contour vegetation barriers (CVB) constitute a cheap option in terms of labour and material requirements. In order to understand the actual adoption and maintenance of CVB, labour requirements of commonly adopted CVB species were evaluated. Labour requirements for the installation of 100 m CVB varied from 7-8 man-days when using cuttings or direct sowing to 15 man-days when installed from nursery seedlings, excluding 8 days for the installation of a dead fence. Maintenance takes 2-4 days per 100m. Phasing the installation over several years is an option to overcome labour constraints. Low labour requirements for establishment and management do not explain the rather low adoption and poor maintenance of vegetation barriers. The labour requirement for establishment of barriers at the beginning of the growing season is not a real constraint. Farmers mostly choose CVB species and planting methods with low labour requirements and prefer species with additional benefits such as thatching grass, oil for soap making and fodder and fruits.At the Central Plateau vegetation barriers can play a vital role in conserving soil and water. Well managed vegetation barriers can contribute to the re-greening of the area.

Domestic (household) biogas plants constitute a growing sub-sector of the anaerobic digestion industry worldwide but have received low interest for improvements. The Chinese dome digester (CDD 1), a major type of domestic biogas plants, is a naturally mixed, unheated and low technology reactor mainly used in rural and pre-urban areas for cooking using animal manure. In this study, a multiphase Computational Fluid Dynamics (CFD) model was applied to evaluate an optimized CDD design and outcomes were compared with results of pilot scale experiments. The optimized digester (CDD2) under goes self-agitating cycles created by the pressure variation from the produced biogas with the aid of a baffle at the top of the reactor, whereas the blank (CDD 1) does not self-agitate. The optimized digester has two pressure zones to improve mixing viz. the self-agitation cycles. The optimized digester is characterized by more, stable and improved hydraulic characteristics and mixing.

Domestic (household) biogas plants constitute a growing sub-sector of the anaerobic digestion industry worldwide but have received low interest for improvements. The Chinese dome digester (CDD 1), a major type of domestic biogas plants, is a naturally mixed, unheated and low technology reactor mainly used in rural and pre-urban areas for cooking using animal manure. In this study, a multiphase Computational Fluid Dynamics (CFD) model was applied to evaluate an optimized CDD design and outcomes were compared with results of pilot scale experiments. The optimized digester (CDD2) under goes self-agitating cycles created by the pressure variation from the produced biogas with the aid of a baffle at the top of the reactor, whereas the blank (CDD 1) does not self-agitate. The optimized digester has two pressure zones to improve mixing viz. the self-agitation cycles. The optimized digester is characterized by more, stable and improved hydraulic characteristics and mixing.