La modélisation d'accompagnement : une méthode de recherche participative et adaptative

Ce chapitre vise à présenter la diversité dans la mise en ½uvre d'un processus de modélisation d'accompagnement, mais aussi les points communs qui en émergent. L'objectif est de décrire pour mieux comprendre, sans intention normative. Nous nous appuyons sur l'analyse des cas d'études et des documents listés dans l'introduction. Notre analyse rassemble des cas concrets et des pratiques qui se réclament de la modélisation d'accompagnement et qui seront donc considérés comme tels dans notre analyse. La compatibilité de la diversité observée avec le cadre d'une adhésion aux principes initiaux de la charte sort du cadre de ce chapitre, elle est traitée dans la conclusion générale de l'ouvrage

Sediment concentration in interrill flow: interactions between soil surface conditions, vegetation and rainfall

A database composed of 673 natural rainfall events with sediment concentration measurements at the field or plot scale was analysed. Measurements were conducted on similar soil type (loess soils prone to scaling phenomenon) to apprehend the variability and complexity involved in interrill erosion processes attributable to soil surface conditions. The effects of the dominant controlling factors are not described by means of equations; rather, we established a classification of potential sediment concentration domain according to combination of the dominant parameters. Thereby, significant differences and evolution trends of mean sediment concentration between the different parameter categories are identified. Further, when parameter influences interact, it allows us to discern the relative effects of factors according to their respective degree of expression. It was shown that crop cover had a major influence on mean sediment concentration, particularly when soil surface roughness is low and when maximum 6-min intensity of rainfall events exceeds 10 mm h(-1): mean sediment concentration decreases from 8.93 g l(-1) for 0-20 per cent of coverage to 0.97 g l(-1) for 21-60 per cent of coverage. The established classification also indicates that the increase of the maximum 6-min intensity of the rainfall factor leads to a linear increase of mean sediment concentration for crop cover over 21 per cent (e.g. from 2.96 g l(-1) to 14.44 g l(-1) for the 1-5 cm roughness class) and to an exponential increase for low crop cover (e.g. from 3.92 g l(-1) to 58-76 g l(-1) for the 1-5 cm roughness class). The implication of this work may bring perspective for erosion prediction modelling and give references for the development of interrill erosion equation. Copyright (C) 2002 John Wiley Sons, Ltd

Incorporating soil surface crusting processes in an expert-based runoff model : STREAM (Sealing and Transfer by Runoff and Erosion related to Agricultural Managment)

International audienc

Modelling sediment concentration in interrill flow as a function of soil surface conditions, vegetation and rainfall

National audienc

Methodology for land use change scenario assessment for runoff impacts: A case study in a north-western European Loess belt region (Pays de Caux, France): A case study in a north-western European Loess belt region (Pays de Caux, France)

International audienceChanges of agricultural land use often induce changes in hydrological behavior of watersheds. Hence, effective information regarding runoff responses to future land use scenarios provides useful support for decision-making in land use planning and management. The objective of this study is to develop a methodology to assess land use change scenario impacts on runoff at the watershed scale. This objective implies translating qualitative information from scenarios into quantitative input parameters for biophysical models. To do so, qualitative information from scenarios should be quantified and spatialized. The approach is based on the combination of 2015 local land use change scenarios (SYSPHAMM method) based on local stakeholders expertise, a model of spatio-temporal allocation of crops to fields (LandSFACTS model) and a watershed runoff model (STREAM model). The study was conducted for regions underlain by silty loamy soils scattered across Northern Europe. It was applied on the Saussay watershed in Upper Normandy (France). The approach is illustrated through runoff assessment of one of the land use change scenarios (characterized by the ending of the set-aside obligation and the disappearance of dairy farming). This scenario appeared relevant for local stakeholders. The methodology presented suggests that assessing local land use scenarios in terms of runoff requires taking into account crop allocation diversity allowed by farmers' decision rules. This requirement accounts for runoff variability at the watershed outlet since crops spatial distribution throughout the watershed, depending on farmers' specific decision rules (i.e. cropping systems), strongly condition runoff phenomenon. Besides, choices regarding scenario implementation (quantification and spatialization) should to be made according to those cropping systems. Accordingly, taking into account crop allocation diversity due to farmers' cropping systems shows that there is a variability in terms of runoff at the watershed outlet (from 19 478 m3 to 35 004 m3 for the winter period and a low-intensity rainfall event for example). This variability can then be explored with local decision makers with the aim of finding solutions reducing runoff risks. The proposed approach provides a useful source of information for assessing the responses of surface runoff of future land use changes. Such scenarios providing impact assessment on runoff should encourage both local policy makers and local actors to actively discuss the future of land use in Upper Normandy

Des modèles pour partager des représentations.

La mise en oeuvre d’une démarche de modélisation d’accompagnement se fonde sur un réseau composé d’individus et d’artefacts parmi lesquels les modèles occupent une place spéciale. Ce chapitre présente les différents modèles développés dans un processus ComMod à des fins de partage de représentations. Porteurs d’une forme de compréhension de systèmes réels (de référence) au sein desquels s’imbriquent dynamiques sociales et biophysiques, les modèles sont des représentations du fonctionnement de ces systèmes. À partir de ces modèles, sont organisés des exercices de simulation exploratoire en impliquant les acteurs du système de référence. Le premier chapitre a introduit les différentes finalités d’usage des modèles dans un processus de modélisation d’accompagnement :– rendre visible des points de vue hétérogènes et les mettre en débat ;– interroger la cohérence de ces points de vue et les conséquences de leur simulationconjointe par rapport au monde réel tel que vécu par les participants ;– proposer un support pour explorer de manière collective des scénarios par dessimulations sur un monde virtuel. La traduction de multiples points de vue sur un système de référence dans des modèles peut prendre différentes voies. Elle s’appuie sur une conceptualisation du système étudié permettant de décrire la part de réalité perçue comme utile par chacun des acteurs, et aboutit au développement d’artefacts spécifiques, mobilisant des techniquesinformatiques et des techniques de mise en situation (jeu de rôles). Une brève introduction explicite le choix des systèmes multi-agents comme mode de représentationprivilégié du domaine étudié. Différentes lignées de modèles sont présentées (modèlesdu domaine, modèles conceptuels, modèles de simulation) ainsi que les étapes d’extractiondes connaissances et d’abstraction, de formalisation et conceptualisation et enfind’implémentation. L’usage des modèles de simulation comme support à l’exploration de72 scénarios est ensuite présenté avant de clore le chapitre sur une analyse de la singularité, de la complémentarité et de la polyvalence de ces modèles, caractéristiques qui autorisent une grande flexibilité dans la mise en oeuvre de la modélisation d’accompagnement

The contribution of crop-rotation organization in farms to crop-mosaic patterning at local landscape scales

International audienceFarming activities are major drivers of the landscape-related ecological patterning because of their multiple influences on both non-arable and arable landscape elements and mosaics. Uncertainties still remain about the way individual farmer decisions and the aggregation of their activities in space contribute to these mosaics at local landscape scales, therefore about possible levers of action in farms for ensuring sustainable landscapes. The general objective of the present study was to give an assessment of the way farms contribute to crop-mosaic patterning at local landscape scales. We developed a method for comparing five contrasted local study cases of agriculture (five farm sets), by combining a statistical modeling of crop-rotation organization in farms, from empirical data, and a crop- mosaic simulation approach, applied in each case. Statistical rules of crop rotation allocation to fields in farms were defined from tests involving the following potential allocation factors: (1) farmhousehold– enterprise, (2) field physical environment and (3) farm territory configuration. The statistical rules set up from each set of factors were implemented in rule-based simulations separately for each of the five local study cases.Weused a raster representation of fields (one pixel by field), to concentrate on crop-rotation management-related effects, independently from the shape of fields and of diverse perennial landscape elements. An index of connectedness was measured for each mosaic, and was used as an indicator of crop-clustering effects due to crop-rotation organization in farms. The results showed that crop- clustering effects at local landscape scales differed according to the following factors of crop-mosaic patterning: (a) the spatial distribution of crop-rotation allocation factors over the field mosaic, (b) the specialization of crop rotations to their allocation factors, and (c) the development of crop rotations over time. These results also demonstrated that crop rotations, even if run as regular crop sequences over time, lead to significant year to year crop-mosaic variability. The results finally made explicit the differences between local study cases. We conclude from these results by pinpointing trade-offs to find between farm and landscape management

Modeling response of soil erosion and runoff to changes in precipitation and cover

Global climate has changed over the past century. Precipitation amounts and intensities are increasing. In this study we investigated the response of seven soil erosion models to a few basic precipitation and vegetation related parameters using common data from one humid and one semi-arid watershed. Perturbations were made to inputs for rainfall intensities and amounts, and to ground surface cover and canopy cover. Principal results were that: soil erosion is likely to be more affected than runoff by changes in rainfall and cover, though both are likely to be significantly impacted; percent erosion and runoff will likely change more for each percent change in rainfall intensity and amount than to each percent change in either canopy or ground cover; changes in rainfall amount associated with changes in storm rainfall intensity will likely have a greater impact on runoff and erosion than simply changes in rainfall amount alone; changes in ground cover have a much greater impact on both runoff and erosion than changes in canopy cover alone. The results do not imply that future changes in rainfall will dominate over changes in land use, since land use changes can often be drastic. Given the types of precipitation changes that have occurred over the last century, and the expectations regarding changes over the next century, the results of this study suggest that there is a significant potential for climate change to increase global soil erosion rates unless offsetting conservation measures are taken