1. Centre for Water Systems, University of Exeter, North Park Road, Exeter EX4 4QF, UK E-mail: sw278@exeter.ac.uk; d.butler@exeter.ac.uk; f.a.memon@exeter.ac.uk
2. Department of Geography, University of Exeter, Rennes Drive, Exeter EX4 4RJ, UK E-mail: s.barr@exeter.ac.uk