Strategies for managing water stress negotiate a complex series of trade-offs and opportunities. Game-changing opportunities for water stressed regions are emerging with new emissions reduction strategies and energy options. These have particular significance for socio-economic development pathways in the marginal drought-prone regions. In this paper, we explore the energy-water-environment nexus in watersheds undergoing acute water stress and energy transitions in the Arab region and the Horn of Africa. A review of published and ongoing scientific activity was used to elaborate four case studies and identify common trade-offs between objectives to reduce water stress, increase productivity and lower energy costs and emissions.

The available scientific evidence base for assessment of these trade-offs was then compared via a discursive process amongst review team members. Collectively, the case studies present a state of the art in available geoscientific methods currently applied in the Arab region to quantify nexus trade-offs for decision-making concerning increasing groundwater use, water harvesting and wastewater reuse across the case studies. The review pursues the wider geographic relevance and scope of this emerging scientific agenda. It identifies global opportunities to boost and progressively enhance the geoscientific information bases for decision-making in the most water stressed regions, as well as direct comparisons with emerging discussion in the Horn of Africa region. Insights for sustainable development decision-makers are highlighted and further scope for the transfer of insights within and beyond the Arab region are discussed.