A coastal urban adaptation model within VIABLE framework
The VIABLE modeling framework allows describing the complexity of interactions in multi-actor systems1. VIABLE has been successfully applied to many climate change and environmental problems by the Research Group Climate Change and Security led by Prof. Dr. Jürgen Scheffran at Universität Hamburg. In brief, VIABLE modelling describes decision-making, interactions, potential conflicts and cooperation in systems of agents striving to achieve their individual goals through action paths by making investments to change the state of (socio-natural) systems in the desired direction.
In a coastal urban adaptation VIABLE model under development, a city subject to sea-level-rise-related hazards needs to define and implement its adaptation strategy. Currently, the city can invest in either of two options (or in a combination of both):
• coastal protection;
• relocation of (part of) the coastal urban territory further inland.
In technical terms, the city has to make a choice about the overall amount of investment and its distribution in between these two options.
The model, developed in Netlogo, runs in yearly time steps. The city starts with a certain amount of urban territory on the coast which is therefore vulnerable to coastal hazards, in this case represented by sea level rise. Over the course of the simulation, the rising sea level incurs damages to the city whenever its coastal defenses are insufficiently developed. The city planner therefore directs part of the income generated by the city towards mitigating these damages through the two options listed above. The planner follows decision rules derived from the VIABLE framework, wherein it finds what the optimal investment in each option would be, based on the current environmental state, and gradually moves towards it.
A snapshot of the model during an exemplary simulation that illustrates the possible adaptive behavior of the city planner. After initial investments towards coastal defenses, the planner directs less and less resources each year. However, as soon as the sea level becomes sufficiently high and damages are intensely felt by the city, the planner moves towards reactive enhancement of defenses in the next time step.