Moctar Dembele¹, Natalie C Ceperley², Sander Zwart³, Gregoire Mariethoz¹ and Bettina Schaefli^2,4, (1)Institute of Earth Surface Dynamics (IDYST), Faculty of Geosciences and Environment (FGSE), University of Lausanne, Lausanne, Switzerland, (2)Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland, (3)International Water Management Institute, PMB CT 112 Cantonments, Accra, Ghana, (4)Now at: Institute of Geography (GIUB), University of Bern, Lausanne, Switzerland