Rarity-Protected Typology Prioritisation for Urban Nature-Based Solutions under Scale-Constrained Planning

Abstract

Planning of nature-based solution interventions in cities typically starts with typology lists, as opposed to calibration of performance models based on local conditions. Such practice generates practical selection problems in Global South cities where floods, heat stress, water pollution, droughts, biodiversity depletion, erosion, air pollution, and lack of equal access to urban nature are often co-occurring challenges even before the availability of performance evidence on costs, land-use, and performance. Typologies of interventions are selected according to scale-weighted functional leverage, functional range, spatial continuity, and medium coupling criteria for keeping only those intervention families that will be assessed further. Scale-Weighted Functional Leverage (SWFL) is calculated for four types of implementation media: water, land, built structures, and hybrid water–land media. Fourteen resilience functions are kept: biodiversity, heat regulation, water-pollution regulation, pluvial flood regulation, coastal flood regulation, river flood regulation, drought regulation, air-pollution regulation, erosion regulation, river navigation improvement, riverbank erosion regulation, social resilience, coastal flood and erosion regulation, and general flood regulation. The most common medium among 32 interventions is water, accounting for 16 interventions, followed by land, responsible for 12 interventions, built structure for three interventions, and one hybrid water and land intervention. Biodiversity is the most common function represented by 19 interventions, compared to single representation of social resilience, river navigation improvement, and riverbank erosion regulation. Neutral SWFL values result in selection of mangrove restoration, green–blue infrastructure, and urban forest systems as leading solutions, and river management and restoration interventions are also important because they help to preserve rare functions of rivers. Ranking of typologies based on priority weighting puts green–blue infrastructure as number one under heat and air categories, raises rainwater harvesting systems under drought and pluvial challenges, and includes urban gardens as a necessity under social and biodiversity categories. Selection of minimum coverage set demonstrates the need for portfolio of interventions as means of achieving broad resilience coverage.