Analysing Trade-offs and Synergies in Land Use for Flood Resilience and Compactness

As cities globally face climate change risks, they are increasingly adopting innovative climate adaptation policies, including 'Nature-based Solutions (NBS)' and advanced planning and social policies. However, the implementation of these strategies by local governments remains limited. Integrating these strategies into urban governance requires interdisciplinary collaboration and inclusive interventions to overcome existing governance inertia (Hölscher et al., 2023). Effective policymaking must align these innovative strategies with new narratives considering wider urban development goals, fostering synergies and co-benefits (Keith et al., 2023). Multi-objective optimisation models play a key role here, involving stakeholders in generating and evaluating alternative land use proposals within spatial decision-making processes. These models focus on balancing competing objectives, using Pareto-optimal solutions to find practical compromises in urban development.

Our focus is on exploring (1) flood-resilient land use and (2) the compatibility of land uses between prioritising flood resilience and compactness, through scenario-based analysis using land use spatial optimisation (LUSO). The target is Toyohashi City, a central city in Japan, which confronts issues dealing with flood risk and strategic land use under the shrinking population. In previous LUSO models, the unit of each objective is different; therefore, it has been difficult to discuss its marginal cost (Yoon et al., 2017). To address this issue, our model adopts the city's 'profit' as a scalarised objective of LUSO, encompassing revenue and expenses influenced by flood resistance, compactness, and minimal land use conversions. (1) Flood-resilient land use is analysed under two types of hazard scenarios: 'uncertain' and 'deterministic'. These scenarios reflect our understanding of which part of the levee might break during a flood. In the 'uncertain' scenario, the specific point of the levee breach is unknown, leading the city to incorporate flood considerations into land use planning across the entire area. Conversely, the 'deterministic' scenario operates on the assumption that the weak point in the levee is known, thereby focusing hazard considerations only on the area surrounding the anticipated breach point. (2) The compatibility of land uses is examined by comparing the land use pattern of ‘never considering compactness’ with that of ‘never considering flood occurrence’. As a result of two analyses, we found that the 'uncertain' scenario is not better than the 'deterministic' scenario in terms of the city’s total 'profit': ensuring equity of flood hazard risk may be costly. In addition, the compatibility analysis identified specific areas that could confront trade-offs between flood avoidance and urban development. This research contributes to understanding the complex dynamics of land use planning in the context of climate change adaptation and demographic shifts.

Hölscher et al. (2023) ‘Strategies for Mainstreaming Nature-Based Solutions in Urban Governance Capacities in Ten European Cities’. Npj Urban Sustainability 3, no. 1. https://doi.org/10.1038/s42949-023-00134-9.

Keith et al. (2023). ‘A New Urban Narrative for Sustainable Development’. Nature Sustainability 6, no. 2: 115–17. https://doi.org/10.1038/s41893-022-00979-5.

Yoon et al. (2017) ‘Multi-Objective Land-Use Allocation Considering Landslide Risk under Climate Change: Case Study in Pyeongchang-Gun, Korea’. Sustainability (Switzerland) 9, no. 12. https://doi.org/10.3390/su9122306.