1. Department of Geography; University of Durham; Durham; DH1 3LE; UK
2. Institut de géographie, Faculté des géosciences et de l'environnement; Université de Lausanne, Bâtiment Anthropole; Lausanne; CH-1015; Switzerland
3. Department of Geography; Loughborough University; Loughborough; Leicestershire; LE11 3TU; UK