Peter M Cox1, Mark S Williamson2, Femke J M M Nijsse2, Chris Huntingford3. 1. College of Engineering, Mathematics and Physical Science, University of Exeter, Exeter, UK. p.m.cox@exeter.ac.uk. 2. College of Engineering, Mathematics and Physical Science, University of Exeter, Exeter, UK. 3. Centre for Ecology and Hydrology, Wallingford, UK.