1. Geography and Spatial Planning Research Centre, IPSE, University of Luxembourg, Route de Diekirch, BP2, L-7220 Walferdange, Luxembourg
2. Centre for Operations Research and Econometrics, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium
3. UMR CESAER, Institut National de Recherche Agronomique, 21065 Dijon, France
4. School of Geosciences, University of Edinburgh, Edinburgh EH9 3JW, Scotland