In the mountainous regions of Northwest Thailand and Vietnam political and economic change and demographic pressure have led to intensification of agricultural systems during the last decade. In the uplands, agricultural land expanded at the expense of forests and traditional swidden systems have been replaced by continuous cropping with reduced or no fallow. Subsistence-based systems are shifting towards external input-dependent production for the market, improving income of farmers in the short run, but partly leading to irreversible loss of environmental functions. The LUCIA model was developed in this context to dynamically simulate biophysical processes triggered by land use (change) in small mountainous catchments in a mechanistic and spatially explicit way. This paper describes the role of the model in integrating data generated under different knowledge domains in an interdisciplinary project to simulate scenarios of land use change, potential environmental impacts and alternative pathways towards sustainable land use. The model structure, stakeholder orientation and coupling with an existing multi-agent system are explained in more detail.