Simulating Rural Environmentally and Socio-Economically Constrained Multi-Activity and Multi-Decision Societies in a Low-Data Context: A Challenge Through Empirical Agent-Based Modeling

Development issues in developing countries belong to complex situations where society and environment are intricate. However, such sites lack the necessary amount of reliable, checkable data and information, while these very constraining factors determine the populations' evolutions, such as villagers living in Sahelian environments. Beyond a game-theory model that leads to a premature selection of the relevant variables, we build an individual-centered, empirical, KIDS-oriented (Keep It Descriptive & Simple), and multidisciplinary agent-based model focusing on the villagers\' differential accesses to economic and production activities according to social rules and norms, mainly driven by social criteria from which gender and rank within the family are the most important, as they were observed and registered during individual interviews. The purpose of the work is to build a valid and robust model that overcome this lack of data by building a individual specific system of behaviour rules conditioning these differential accesses showing the long-term catalytic effects of small changes of social rules. The model-building methodology is thereby crucial: the interviewing process provided the behaviour rules and criteria while the context, i.e. the economic, demographic and agro-ecological environment is described following published or unpublished literature. Thanks to a sensitivity analysis on several selected parameters, the model appears fairly robust and sensitive enough. The confidence building simulation outputs reasonably reproduces the dynamics of local situations and is consistent with three authors having investigated in our site. Thanks to its empirical approach and its balanced conception between sociology and agro-ecology at the relevant scale, i.e. the individual tied to social relations, limitations and obligations and connected with his/her biophysical and economic environment, the model can be considered as an efficient "trend provider" but not an absolute "figure provider" for simulating rural societies of the Nigrien Sahel and testing scenarios on the same context. Such ABMs can be a useful interface to analyze social stakes in development projects.Rule-Based Modelling, Rural Sahel, Confidence Building, Low-Data Context, Social Criteria

Characteristics and causes of natural and human-induced landslides in a tropical mountainous region: the rift flank west of Lake Kivu (Democratic Republic of the Congo)

Tropical mountainous regions are often identified as landslide hotspots with growing population pressure. Anthropogenic factors are assumed to play a role in the occurrence of landslides in these densely populated regions, yet the relative importance of these human-induced factors remains poorly documented. In this work, we aim to explore the impact of forest cover dynamics, roads and mining activities on the characteristics and causes of landslides in the rift flank west of Lake Kivu in the Democratic Republic of the Congo (DR Congo). To do so, we compile a comprehensive multi-temporal inventory of 2730 landslides. The landslides are of different types and are grouped into five categories that are adapted to study the impact of human activities on slope stability: old (pre-1950s) and recent (post-1950s) deep-seated landslides, shallow landslides, landslides associated with mining and landslides associated with road construction. We analyse the landslides according to this classification protocol via frequency–area statistics, frequency ratio distribution and logistic regression susceptibility assessment. We find that natural factors contributing to the cause of recent and old deep-seated landslides were either different or changed over time. Under similar topographic conditions, shallow landslides are more frequent, but of a smaller size, in areas where deforestation has occurred since the 1950s. We attribute this size reduction to the decrease in regolith cohesion due to forest loss, which allows for a smaller minimum critical area for landsliding. In areas that were already deforested in the 1950s, shallow landslides are less frequent, larger and occur on less steep slopes. This suggests a combined role between regolith availability and soil management practices that influence erosion and water infiltration. Mining activities increase the odds of landsliding. Landslides associated with mining and roads are larger than shallow landslides but smaller than the recent deep-seated instabilities, and they are controlled by environmental factors that are not present under natural conditions. Our analysis demonstrates the role of human activities on the occurrence of landslides in the Lake Kivu region. Overall, it highlights the need to consider this context when studying hillslope instability characteristics and distribution patterns in regions under anthropogenic pressure. Our work also highlights the importance of using landslide classification criteria adapted to the context of the Anthropocene.</p

Using the DSSAT Model to Support Decision Making Regarding Fertilizer Microdosing for Maize Production in the Sub-humid Region of Benin

Fertilizer microdosing is being widely promoted across sub-Saharan Africa, yet all recommendations regarding this technology are derived from short-term studies. Such studies are insufficient to properly assess the production risk caused by climatic variability. To address this issue while avoiding costly long-term experiments, a common and well accepted strategy is to combine results from short-term experiments with validated dynamic crop models. However, there have been few documented attempts so far to model fertilizer microdosing under sub-humid tropical conditions. The objective was therefore to evaluate the potential of the DSSAT model for simulating maize response to fertilizer microdosing, and to use the validated model to assess the effects of inter-annual rainfall variability on maize productivity and economic risk. The model was calibrated and validated against data from a 2-year on-station experiment (2014 and 2015) with 2 levels of hill-placed manure and five mineral fertilization options including broadcast and fertilizer microdosing. Model simulations were in good agreement with the observed grain and biomass yields for conventional broadcast fertilization, with relative RMSE and d-values of 12% and 0.96 for grain and 8% and 0.97 for biomass, respectively. For fertilizer microdosing, the N stress coefficient needed to be adjusted to avoid occurrence of large N stresses during simulation. After optimization, the model adequately reproduced grain yields for fertilizer microdosing, with relative RMSE of 10%. Considering the long-term scenario analysis, the use of the validated model showed that the application of 2 g of NPK15−15−15 fertilizer + 1 g urea per hill (equivalent to 23.8 kg N ha−1, 4.1 kg P ha−1 and 7.8 kg K ha−1) improved both the minimum guaranteed yield and the long-term average without increasing inter-annual variability and the economic risk compared to unfertilized plots. Even though combining microdosing with manure (1–3 t ha−1) was economically slightly riskier than microdosing alone, this risk remained low since a value-cost ratio of 2 could be achieved in almost 100% of the years. Furthermore, combined application consistently reduced the inter-annual yield variability. Considering this as well as the other benefits of manure for soil health, combining microdosing with small quantities of manure would be recommended to increase the sustainability of the system

“Cropland characteristics and extent of soil loss by rill and gully erosion in smallholder farms in the KIVU highlands, D.R. Congo”

Soil erosion is a widespread phenomenon threatening the sustainability of agricultural production in the South-Kivu highlands (eastern D.R. Congo), as is the case in other cultivated areas of the East-African highlands. However, quantitative estimates of soil erosion on farm are scarce. To address this, the extent of erosion and associated explanatory factors were studied in two representative watersheds across a wide range of cropping systems and soil characteristics. Rill and gully erosion volumes were measured every 2 weeks in 90 fields by the transect methods during four successive long (SA) and short (SB) rainy seasons (2015–2017). Additionally, field characteristics and rainfall were collected. Results show that the average soil loss rate was significantly different between seasons, with rates of 3.1 and 1.9 mm in season A-2015, 1.8 and 2.7 mm in season B-2016, 2.2 and 3.3 mm in season A-2016 and 3.2 and 3.8 mm in Season B-2017 for minimum rill (damage area) and gully erosion (whole field), respectively. As a result of differences both in natural factors (e.g., precipitation and slope steepness) and management conditions (cropping systems and soil cover) across farmers' fields, there was a large variability in cumulative soil erosion rates across fields, from 0.03 to 18 mm for minimum rill erosion and from 0.13 to 11.7 mm for gully erosion rates over the 4 seasons. For 41% of fields, rill erosion rates are higher than the tolerable soil loss generally set at 12.5 t/ha/year (or 1 mm/year) for the most fertile soils. Low minimum rill erosion rates tended to be associated with high pH, sum of bases and effective CEC, while high erosion rates were associated with high topsoil depth in both watersheds. Cassava-based cropping systems tended to be associated with high rill erosion rates, while higher rainfall increased both rill and gully erosion rates. Overall, the very high measured rill erosion rates suggest the urgent need for implementation of erosion control strategies. The results could be used to prioritize sites at risk of water erosion at the small watershed scale in order to install mitigation measures

Driving Factors of the Hydrological Response of a Tropical Watershed: The Ankavia River Basin in Madagascar

Understanding the hydrological behavior of watersheds (WS) and their driving factors is crucial for sustainable water resources management. However, at large scales, this task remains challenging due to the spatial heterogeneity in landscapes, topography and morphology (T), land cover (LC), geology (G), and soil properties (S). In this context, the aim of this study was to identify the key factors that influence the hydrological signatures of four watersheds: Ankavia (WS1: 55% forest cover), Ankaviabe (WS2: 77% forest cover), Sahafihitry (WS3: 41% forest cover), and Antsahovy (WS4: 48% forest cover), over a 10-month study period. These catchments are located within the SAVA region of northeastern Madagascar and have a humid tropical climate. We investigated the relationship between selected catchment descriptors and hydrological signatures by using a Pearson coefficient-based correlation matrix. More specifically, catchment descriptors (extracted from T, LC, G, and S) were correlated with the following hydrological signatures: base flow index (BFI), mean runoff coefficient (rc), mean peak flow (Qp), mean runoff event time scales (ts), high flows (Q5), low flows (Q95), and mean discharge (q_mean). The analysis revealed that land cover, soil properties, and geology seem to be the best predictors for BFI and Q95, while soil properties mainly govern rc, Qp, Q5, ts, and q_mean. These findings provide valuable insights into the key drivers of hydrological behavior that can inform water resource management strategies. In particular, WS2 exhibits better flood buffering capacity but also experiences lower base flows in the dry season, potentially due to higher evapotranspiration. Conversely, WS3 and WS4 (and to a lesser extent WS1) have lower flood buffering capacity, but these watersheds encounter less pronounced low flows in the dry season due to higher BFIs, possibly attributable to lower evapotranspiration rates. The results underscore the importance of responsible land use practices and conservation efforts, which are essential for the sustainable development of the region. By incorporating these practices into water management strategies, we can help ensure a more stable and reliable water supply for communities and ecosystems within the region

Evolution of overland flow connectivity in bare agricultural plots

Soil surface roughness not only delays overland flow generation but also strongly affects overland flow distribution and concentration. Previous studies generally aimed at predicting the delay in overland flow generation by means of a single parameter characterizing soil roughness. However, little work has been done to find a link between soil roughness and overland flow dynamics. This is made difficult because soil roughness and hence overland flow characteristics evolve differently depending on whether diffuse or concentrated erosion dominates. The present study examines whether the concept of connectivity can be used to link roughness characteristics to overland flow dynamics. For this purpose, soil roughness of three 30-m2 tilled plots exposed to natural rainfall was monitored during 2 years. Soil micro-topography was characterized by means of photogrammetry on a monthly basis. Soil roughness was characterized by the variogram, and overland flow connectivity by a functional connectivity in- dicator called the Relative Surface Connection function (RSCf). Overland flow hydrograms were generated by a physically-based overland flow model (FullSWOF_2D) on 1-cm resolution digital elevation models. The devel- opment of eroded flow paths at the soil surface not only reduced the delay in overland flow generation but also resulted in a higher continuity of high flow velocity paths, an increase in erosive energy and a higher rate of in- crease of the overland flow hydrograph. Overland flow dynamics were found to be highly correlated to the RSCf characteristic points. This high correlation shows the potential of the RSCf both to serve as a quantitative link between soil roughness and overland flow generation by providing information regarding overland flow dynamics and to improve the overland flow hydrograph prediction

Short- and medium-term impact of manual tillage and no-tillage withmulching on banana roots and yields in banana-bean intercroppingsystems in the East African Highlands

tBanana-bean intercropping systems are common in the bimodal rainfall areas of the East African High-lands and are characterized by low banana productivity. In these systems, the soil is tilled manually twicea year before bean planting with potentially damaging effects to the shallow banana root system. No-tillage with mulching (NT + M) may constitute an interesting alternative to conventional manual tillage(CMT) to avoid such root damage and improve banana productivity. The objectives of this study weretherefore (i) to assess tillage-induced damage to the banana rooting system and its subsequent recovery,and (ii) to evaluate the impact of three NT + M systems vs. CMT on banana root distribution and bananabunch weight. At two sites in the D.R. Congo, the cord root length density (RLD) and fresh weight (FW)were monitored monthly in the top 0.2 m of the soil over a 5 to 6-month period following manual tillage,and compared with NT + M plots. Immediately after tillage and on average over the two sites, cord RLDand FW in the top 0.1 m of the soil were reduced on average to 15% and 16%, respectively, of the levelsobserved under NT + M. At 0.3 m from the rhizome, cord roots needed 2–4 months to recover to a levelsimilar to the one observed prior to tillage. On average over the two sites, direct root damage by tillagecaused the loss of 47% and 63% of the RLD and FW observed in NT + M plots, respectively. The remainingrooting deficit (38% of RLD and 21% of FW) was hypothesized to originate from differences in root growthconditions unrelated to immediate mechanical root damage. There was no evidence that the mechanicaldamage of roots by tillage affected banana growth in the short term. The medium-term effect of CMT andNT + M treatments was evaluated at three sites (two in D.R. Congo and one in Rwanda) 30 months afterbanana planting. At two sites out of three, root density profiles indicated lower rooting densities in the top0.1 m of the soil in CMT plots compared with NT + M plots. Banana bunch weight was consistently lowerin CMT plots compared with NT + M plots. Compared with NT + M, CMT appears to affect banana rootingand bunch weight in the medium term under the pedo-climatic conditions of the East African Highlands.No-tillage with mulching may constitute an alternative to manual tillage to enhance the sustainabilityof these systems but its impact on the whole intercropping system’s productivity must be verified

Testing the impact of social forces on the evolution of Sahelian farming systems: a combined agent-based modeling and anthropological approach

This article presents the results of a methodology based on an extensive sociological fieldwork in three different sites settled along a gradient of aridity in Nigerien Sahel. This fieldwork led to build a set of rules for the behaviour of individuals in non-pastoralist villages. We implemented these rules into an agent-based model simulating three village archetypes. Each archetype includes biophysical, economical, social agricultural and livestock modules. Results from simulations with no social transition processes show that villages specialize themselves into different economic activities according to natural resource specificities: A decreasing intensification gradient is observed from the most favoured site, with more local productions and good ecological indicators, to the less-favoured site, with a growing proportion of the population wealth coming from migration remittances and “off-shore” livestock. Two family transition processes were implemented, following field observations and literature-based hypotheses: family organizations evolve between a patriarchal mode and a non-cooperative mode following tensions due to income redistribution. Family inheritance systems evolve from a “customary” one-heir mode to a “local Muslim” mode in which all males inherits land. This evolution depends on family tensions due to land availability. Once introducing these processes, the population of each site differentiates itself into specialized groups according to size, assets and social status. Meanwhile, the group proportions and specializations strongly vary according to the sites but they are all characterized by the emergence of individualistic family types and the increase of the village populations’ robustness

Simulating rural environmentally and socio-economically constrained multi-activity and multi-decision societies in a low-data context: A challenge through empirical agent-based modeling

Development issues in developing countries belong to complex situations where society and environment are intricate. However, such sites lack the necessary amount of reliable, checkable data and information, while these very constraining factors determine the populations' evolutions, such as villagers living in Sahelian environments. Beyond a game-theory model that leads to a premature selection of the relevant variables, we build an individual-centered, empirical, KIDS-oriented (Keep It Descriptive & Simple), and multidisciplinary agent-based model focusing on the villagers\' differential accesses to economic and production activities according to social rules and norms, mainly driven by social criteria from which gender and rank within the family are the most important, as they were observed and registered during individual interviews. The purpose of the work is to build a valid and robust model that overcome this lack of data by building a individual specific system of behaviour rules conditioning these differential accesses showing the long-term catalytic effects of small changes of social rules. The model-building methodology is thereby crucial: the interviewing process provided the behaviour rules and criteria while the context, i.e. the economic, demographic and agro-ecological environment is described following published or unpublished literature. Thanks to a sensitivity analysis on several selected parameters, the model appears fairly robust and sensitive enough. The confidence building simulation outputs reasonably reproduces the dynamics of local situations and is consistent with three authors having investigated in our site. Thanks to its empirical approach and its balanced conception between sociology and agro-ecology at the relevant scale, i.e. the individual tied to social relations, limitations and obligations and connected with his/her biophysical and economic environment, the model can be considered as an efficient "trend provider" but not an absolute "figure provider" for simulating rural societies of the Nigrien Sahel and testing scenarios on the same context. Such ABMs can be a useful interface to analyze social stakes in development projects