1. a Environmental Change Institute University of Oxford , 5 South Parks Road, Oxford , OXI3UB , United Kingdom
2. b Department of Geography , University of the Free State , PO Box 339, Bloemfontein , 9300 , South Africa E-mail:
3. c Research School of Earth Sciences The Australian National University , Canberra , ACT , 0200 , Australia
4. d Sheffield Centre for International Drylands Research , University of Sheffield , Winter Street, Sheffield , S10 2TN , United Kingdom