1. Department of Geography, Université Catholique de Louvain, Place Louis Pasteur 3, B-1348 Louvain-la-Neuve, Belgium, Department of Environmental Sciences and Land Use Planning, Génie Rural, Université Catholique de Louvain, Croix du Sud 2, BP 2, B-1348 Louvain-la-Neuve, Belgium, National Institute for Public Health and the Environment, PO Box 1, 3720 BA Bilthoven, The Netherlands, and Netherlands Environmental Assessment Agency (MNP), PO Box 303, 3720 AH Bilthoven, The Netherlands