1. Introduction

To reach sustainability targets, there must be a quicker and more radical transformation of built environments ^{[1][2][3][4][5]}. Characteristics of more sustainable built environments include increased densities, mixed-use planning, improved energy and water efficiency and the use of biobased materials and renewable energy systems.

However, the onset of climate change also means that built environments are faced with unprecedented environmental hazards such as increasing temperatures, heatwaves, droughts, storms, and flooding^{[6][7][8][9][10]}. Built environments, therefore, must also be able to respond to environmental hazards. Characteristics of resilient built environments include flood defences, strengthened structural elements and robust energy and water systems which can withstand extreme weather conditions.

2. Conflicts between Resilience and Sustainability

A review of the concepts and characteristics of sustainable and resilient built environments indicates that there are conflicts between the two approaches.

Sustainable built environment approaches are concerned with reducing environmental impacts and achieving more efficient performance. For instance, bio-based materials and more energy and water-efficient systems are advocated. Resilient built environment approaches on the other hand are concerned with strengthening structure and developing more robust systems. This may be achieved through additional materials which are used to strengthen structures and more reliable, but often less efficient, equipment and systems.

3. Resilient Sustainability

Achieving sustainable development and climate change targets will require approaches that integrate sustainability and resilience.

This can be achieved through integrating the concepts of sustainability and resilience in the form of sustainable resilience. Resilient sustainability can be understood as developing and maintaining capabilities required for sustainability, despite disturbances. López-Ridaura et al., describe this in the following way:

“..the degree to which a system is sustainable will depend on its capabilities to pro-duce…, a specific combination of goods and services that satisfies a set of goals ..even when facing..‘extreme’ …variations” ^[11].

This definition enables sustainability and resilience objectives to be combined and that development must focus on achieving sustainability capabilities. With these in place, it confirms that these must be maintained through a focus on resilience.

A range of built environment resilience frameworks exist. These include the City Resilience Index developed by Arup, the City Resilience Profiling Tool developed by UN-Habitat and disaster resilience indicators developed by ISO as well as those the developed for US and South African cities^{[12][13][14][15][16]}.

Suárez et al., points out that these frameworks do not include sustainability and focus on the recovery and adaptation of engineering and ecological systems^[17]. They do not focus on transformation and social change central to definitions of resilient by Folke ^[18] . Elmqvist et al., points out that urban systems can have many different development trajectories and that resilience frameworks select those they wish to strengthen ^[19]. For instance, some aim to help cities cope with health, social or natural disaster crises such as COVID-19 ^[17].

4. Resilient Sustainability Measurement and Evaluation (RESUME) Framework

The Resilient Sustainability Measurement and Evaluation (RESUME) framework aims to ensure that sustainable development trajectories are maintained. It combines sustainability objectives and resilience principles to propose resilient sustainable built environment capabilities and characteristics^[20]. These are shown in the table below.

5. Discussion

The RESUME tool includes criteria that measure these resilient sustainable built environment capabilities and characteristics and can be used to evaluate urban areas and has been used to assess informal settlements in South Africa.

The RESUME approach differs from conventional urban resilience frameworks in two distinct ways.

First, instead of a broad focus on the recovery of engineering and ecological systems, resilient sustainability only addresses the maintenance and development of urban systems and characteristics that support sustainability. Thus, the recovery of systems or aspects that do not directly support sustainability is not prioritized.

Second, social transformation and change are central to the tool. Achieving change that enables sustainability is the goal of resilient sustainability which selectively strengthens systems that support this. Thus a disruptive event is used to change and develop more sustainable systems within a neighborhood instead of trying to support the recovery of systems and characteristics that were unsustainable.

6. Conclusion

By combining sustainability and resilience, resilient sustainability is highly relevant to resource and capacity-constrained areas, as the framework provides a mechanism for the prioritization of human and sustainability issues. By addressing both sustainability and resilience simultaneously the approach also enables more efficient and focused implementation and will be of interest to professionals, communities and governments needing to embark on infrastructure development programmes.

7. Acknowledgements

This paper draws on a paper by Gibberd which develops the concept of resilient sustainability and applies it through the RESUME framework to assess neighbourhoods^[20].