Applying the Global RCP-SSP-SPA Scenario Framework at Sub-National Scale: A Multi-Scale and Participatory Scenario Approach
To better anticipate potential impacts of climate change, integrated information about the future is required: future climate, future society and economy, and future adaptation and mitigation. To address this need, a global RCP (Representative Concentration Pathways), SSP (Shared Socio-Economic Pathways), and SPA (Shared climate Policy Assumptions) (RCP–SSP–SPA) scenario framework has been developed by the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC-AR5). However, full application of this global framework to develop site-specific and policy-relevant information at a sub-national scale introduces two key challenges: (i) added complexity in capturing the multiple dimensions of change, and (ii) issues of scale; perhaps for this reason, there are few full applications of this new framework. Here, we present an integrated multi-scale hybrid scenario approach that combines both expert-based and participatory methods. The framework has been developed and applied within the DECCMA (DEltas, vulnerability and Climate Change: Migration and Adaptation) project with the purpose of exploring migration and adaptation in three deltas across South Asia and West Africa: (i) the Ganges–Brahmaputra–Meghna (GBM) delta (Bangladesh/India), (ii) the Mahanadi delta (India), and (iii) the Volta delta (Ghana). Using a climate scenario that encompasses a wide range of impacts, from low to high, (RCP8.5) combined with three SSP-based socio-economic scenarios (SSP2, SSP3, and SSP5), we generate highly divergent and challenging scenario contexts across the multiple scales against which robustness of the human and natural systems within the deltas are tested. On top of this, we impose four distinct adaptation policy trajectories (APTs): Minimum intervention, Economic capacity expansion, System efficiency enhancement, and System restructuring, which describe alternative future bundles of adaptation actions and measures under different economic and social trajectories. The paper highlights the importance of multi-scale (combined top-down and bottom-up) and participatory (joint expert-stakeholder) scenario methods for addressing climate change uncertainty in adaptation decision-making. The framework facilitates improved integrated assessments of the potential impacts and plausible adaptation policy choices (including migration) under uncertain future changes in climatic, environmental, and socio-economic conditions. The concept, methods, and processes presented are transferrable to other sub-national socio-ecological settings with multi-scale challenges.