1. Research Engineer, Centre for Water Systems, College of Engineering, Mathematics, and Physical Sciences, Univ. of Exeter, North Park Rd., Harrison Bldg., Exeter EX4 4QF, U.K. (corresponding author).
2. Professor, Centre for Water Systems, College of Engineering, Mathematics, and Physical Sciences, Univ. of Exeter, North Park Rd., Harrison Bldg., Exeter EX4 4QF, U.K.
3. Senior Hydrologist, HR Wallingford, Howbery Business Park, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BA, U.K.
4. Mathematician, Smith Institute, Surrey Technology Centre, Surrey Research Park, Guildford, Surrey GU2 7YG, U.K.