Identifying transformative decisions: A dual approach to adaptation pathways design using forward-exploration and backcasting

Adaptation is needed to keep deltas and coastal zones liveable under changing climatic and socio-economic conditions. To date, adaptation is mostly small scale with incremental adaptation measures, while in some areas more fundamental transformative decisions are required in the future, such as changing objectives and land use. Here, we introduce an adaptation pathways method that uses forward-exploration and backcasting to study the impact of fundamental decisions on the solution space. For this, we extend the Dynamic Adaptive Pathways Planning (DAPP) approach and refer to this as DAPP-Δ (DAPP-delta) with Δ representing the fundamental decisions. Following the traditional DAPP approach, we explore alternative sequences of adaptation measures to continue to achieve objectives under changing conditions. New to the method is the backcasting of critical implementation paths from different envisioned future states, including changes in land use. Additionally, we identify synergies and conflicts between the forward-looking pathways and backcasting implementation paths. We use the southwest of the Netherlands as an illustrative case study. In this region, multiple adaptation tipping points are projected due to sea-level rise and economic changes, while simultaneously large-scale investments in aging infrastructure are expected. The results show that the DAPP-Δ method a) helps to identify pivotal adaptation decisions that goes beyond incremental adaptation and includes transformative decisions; b) effectively reveals the risk of maladaptation; and c) illustrates the necessity to include multiple changes in the analysis, as they together determine investments in the area and with that the solution space.