Clemens has been able to engage in policy development and resource use planning in such diverse areas as Regional Victoria (AUS), the Mekong Delta and rural Laos, where he has worked with municipal authorities, national and subnational stakeholders, as well as residents. His publications span a diverse array of topics, such as climate adaptation, decision analysis, sustainable livelihoods and material flow analysis.

Prior to joining SEI, Clemens was a faculty member at the School of Environment, Resources and Development of the Asian Institute of Technology, supervising students and conducting research in the field of Natural Resources Management. Before that, he held various positions at the CSIRO (Australia), the Mekong Institute (Thailand), and the Universities of Klagenfurt and Vienna (Austria). He is currently a visiting professor at the University of Vienna.