Unintended consequences of climate change mitigation for African river basins

Global policies to mitigate climate change suggest the need of pricing greenhouse gas emissions to attain rapid emissions reductions. The efficacy of these measures is generally assessed at the global or regional scale, while their local impacts are often difficult to anticipate and are consequently overlooked in many analyses. This study addresses this gap by investigating how multisector dynamics across interconnected Water-Energy-Food (WEF) systems at the local scale are impacted by global climate change mitigation efforts. We use a detailed river basin scale operational model of the Zambezi Watercourse in Southern Africa that enables the exploration of synergies, tradeoffs, and vulnerabilities for the local WEF systems. Our analysis includes more than 7,000 scenarios that combine different climate and socio-economic projections with alternative mitigation policies. Future irrigation demands are generated by systematically sampling the Shared Socioeconomic Pathways components along with multiple Shared Policy Assumptions. Future water availability is instead produced by forcing local hydrological models with bias-adjusted climate projections from different combinations of global and regional climate models for different Representative Concentration Pathways. Our results contribute quantitative evidence of the unintended vulnerabilities that may emerge in the Zambezi Watercourse. Policy fragmentation between developed and developing countries in their approach to land use change emissions can have negative side effects on local water demands, producing favorable conditions for the realization of extensive agricultural projects in Africa where the price associated to the land-use change emission is low. This generates irrigation demands two times higher than under globally coordinated approaches to emissions reductions and constrains the availability of water resources for hydropower production or the provision of ecosystem services. Analogous vulnerabilities could impact many river basins in Southern and Western Africa. It is critical to connect global climate change mitigation policies to local dynamics for a better understanding of the full range of possible future scenarios while supporting policy makers in prioritizing sustainable mitigation and adaptation solutions.