1. Territorial Division for the Northern and Picardie Regions, Cerema (Center for studies and expertise on Risks, Environment, Mobility, and Urban and Country Planning), 2 rue de Bruxelles CS 20275 59019, Lille, Cédex 59000, France, cyprien.richer@developpement-durable.gouv.fr - sophie.hasiak@developpement-durable.gouv.fr