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Résumé

Maelia est une plateforme de modélisation et de simulation, multi-agents, permettant d’évaluer, à l’échelle du territoire, les impacts environnementaux, économiques et sociaux des changements combinés de normes de gestion de l’eau, d’activités agricoles et globaux (démographie, dynamique d’occupation du sol et changements climatiques).

Actuellement, cette plateforme permet de représenter à des résolutions spatiale et temporelle fines les interactions entre les activités agricoles (choix d’assolement, conduite des différents systèmes de culture au sein de chaque système de production), l’hydrologie des différentes ressources en eau (basé sur les formalismes de la plateforme SWAT®) et la gestion des ressources en eau (lâchers, restrictions, choix entre ressources).

Plus généralement, Maelia propose une architecture logicielle pour traiter des questions concernant les interactions entre activités agricoles, dynamiques du paysage agricole et gestion des ressources naturelles à l’échelle du territoire. De manière originale, elle permet de représenter le fonctionnement et les interactions entre les 4 grands sous-systèmes d’un système socio-écologique : (i) l’écosystème, (ii) le système de ressources générées par cet écosystème, (iii) les activités des usagers de ces ressources et (iv) le système de gouvernance qui cherche à réguler les interactions entre usagers et ressources.

Des projets d’extension des fonctionnalités de Maelia sont en cours. Ils permettront de traiter les questions relatives aux interactions entre systèmes de grande culture et d’élevage, cycle des nutriments, érosion, régulations biologiques et régulation du climat.

MAELIA est distribuée sous licence GPLv3. Une aide à l’utilisation de la documentation peut être trouvé ICI.

Brief English description

Maelia is a multi-agent modelling and simulation platform for assessing environmental, economic and social impacts of combined changes of water management norms, agricultural activities and global changes (demography, land-use changes and climate changes).

Currently, this platform allows to handle at fine spatio-temporal scales the interactions between agricultural activities (rotation and crop management strategies within each production system), the hydrology of the different water resources (based on the SWAT® model’s formalisms) and the water resources management (water withdrawals, restrictions, choices between resources). It provides a software architecture to handle the questions of interaction between agriculture and environment at the regional scale.

More generally, Maelia provide user with a software architecture to address questions about the interactions between agricultural activities, the agricultural landscape dynamics and the management of natural resources at the landscape level. Originally, Maelia allows to simulate behaviour of and interactions between the four main core sub-systems of social-ecological systems: (1) resource systems (e.g. hydrological systems), (2) resource units (e.g. water volume and flow), (3) governance systems (e.g. which regulate uses and manage water resources) and (4) users (e.g. individuals and collectives who use water).

New developments in MAELIA are ongoing. They will allow to address issues related to the interaction between arable and livestock farming systems, nutrient cycling, erosion, biological regulations and climate regulation, at the landscape level.

Maelia is distributed under GPLv3.

Hydrologic aspects

Maelia simulates the water flow through a complex network of water bodies (e.g. rivers, groundwater, reservoir, dams, channels), taking into account the numerous pressures from industry, drinking water providers and farmers. Hydrology representation is based on the SWAT® model’s formalisms (Soil and Water Assessment Tool®).

Rivers and groundwaters of the Garonne Amont basin

Agricultural aspects

Agricultural pressures play a major role in low-water management. Therefore, a fine model of the farmer’s activities has been developed. The forest and grassland growth modelling is handled by a simplified version of SWAT®‘s formalisms while AqYield, an empirical crop model is used for simulating crop growth. This latter represents effects of agricultural practices on day-to-day soil water dynamics and, in turn, crop growth.

The spatial distribution of cropping systems (rotation and crop management strategies) within farms can be either a pre-defined inputs or simulated by the cropping plan decision module that is based on a Belief-Desire-Intention architecture. Crop management strategies are represented through a set of decision rules (nested IF THEN rules) to trigger tillage, sowing, fertilization, hoeing, irrigation, and harvesting.

Social aspects

Two main types of social dynamics are represented in Maelia: the socio-economic phenomena (land use changes, domestic and industrial water withdrawals and discharges) and the regulation activities of dam managers and local state services (water use restrictions).

Water releases from dams and restrictions of agricultural water withdrawals during the low-water period are simulated, day after day, according to decision rules (nested IF THEN rules) of corresponding actors.

Data integration

Implementation of the MAELIA platform requires integration of more than 20 types of data: soil, climate, elevation, land cover, water withdrawals and release points, rivers, small individual-managed dams, collectively managed dams, groundwater, farm islets spatial distribution, cropping systems…

GIS pre-processing routines have been developed to strongly facilitate implementation of the platform in a new river basin. They provide a detailed and coherent space-time representation of the complexity of the structure and the initial state of the studied management situation.

Implementation

The Maelia multi-agents simulation model has been implemented with GAMA®; an open-source generic agent-based modeling and simulation platform with powerful features in terms of GIS integration or high-level tools (e.g., decision-making or clustering algorithms).

3D visualisation
3D Gama’s visualisation of some of the Maelia’s entities

Conclusion

The Maelia Integrated Impact Assessment platform deals with key challenges of modelling social-ecological systems. First, it represents dynamic interactions between human activities and ecological processes on the one hand and governance systems on the other hand. Second, it represents these interactions at the relevant spatiotemporal resolutions to handle actual problems of organizations in charge of water management and of issues of the main water users: the farmers. Maelia seems to have reached its objective to develop relevant knowledge for decision-makers since it is currently adapted to develop decision support systems for local water resource managers.

Multi-Agents for EnvironmentaL norms Impact Assessment