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To cite this version:Thomas Houet, Marine Gremont, Laure Vacquié, Yann Forget, Apolline Marriotti, et al.. Downscaling scenarios of future land use and land cover changes using a participatory approach: an application to mountain risk assessment in the Pyrenees (France) . Regional Environnemental Change, Springer, 2017, 17 (8) Better understanding the pathways through which future socio-economic changes might influence land 19 use and land cover changes (LULCC) is a crucial step in accurately assessing the resilience of 20 societies to mountain hazards. Participatory foresight involving local stakeholders may help building 21 fine-scale LULCC scenarios that are consistent with the likely evolution of mountain communities. 22This paper develops a methodology that combines participatory approaches in downscaling socio-23 economic scenarios with LULCC modelling to assess future changes in mountain hazards, applied to a 24 case study located in the French Pyrenees. Four spatially-explicit local scenarios are built each 25 including a narrative, two future land cover maps up to 2040 and 2100, and a set of quantified 26 LULCC. Scenarios are then used to identify areas likely to encounter land cover changes 27 (deforestation, reforestation and encroachment) prone to affect gravitational hazards. In order to 28 demonstrate their interest for decision-making, future land cover maps are used as input to a landslide 29 hazard assessment model. Results highlight that reforestation will continue to be a major trend in all 30 scenarios and confirm that the approach improves the accuracy of landslide hazard computations. This 31 validates the interest of developing fine-scale LULCC models that account for the local knowledge of 32 stakeholders. 33

Abstract. Vulnerability is a complex concept involving a variety of disciplines from both the physical and socio-economic sciences. Currently, two opposite trends exist: the physical approach in which vulnerability is analysed as a sum of potential impacts on elements at risk and the social approach in which vulnerability is mostly viewed as a combination of socio-economic variables determining people's ability to anticipate, cope with and recover from a catastrophic event. Finding a way to combine these two approaches is a key issue for a global vulnerability assessment. In this paper we propose to combine elements from these two approaches through the analysis of the potential consequences of a high-magnitude flood event (recurrence interval (RI) > 100 years) on human and material stakeholders. To perform our analysis, we choose to upgrade an existing index, the Potential Damage Index (PDI; Puissant et al., 2013), by including social criteria. The PDI was originally developed to assess the physical consequences of hazards on the elements at risk (people, building and lands). It is based on the calculation of three sub-indices representing different types of direct and indirect consequences: physical injury consequences (PIC), structural and functional consequences (SFC), indirect functional consequences (IC). Here, we propose to add a fourth sub-index representing the social consequences. This new sub-index, called social consequences (SC) is obtained by combining criteria derived from INSEE French census data and a risk-perception survey conducted in the field. By combining the four indices (PIC, SFC, IC and SC), we managed to create a new index called the Potential Consequences Index (PCI). The new PCI was tested on the Upper Guil catchment to assess the consequences of a high-magnitude flood event (RI > 100 years). Results of the PDI were compared with the PCI and show significant differences. The upgrade to the PDI method provided us with many inputs. The introduction of elements from social vulnerability added an extra dimension to the total consequence map. It allowed us to qualify the potential physical consequences (physical injury, structural and functional consequences) on elements at risk by considering the global resilience of local communities.