Cities are shaped by their built environment, infrastructure, urban economy, and population. Whether taken collectively or broken down to the constituent elements, cities are vulnerable to the impacts of climate change, particularly extreme weather events such as heatwaves and flooding. Katie Jenkins, an urban systems modeller at the University of Oxford, reveals how new modelling techniques can help decision-makers to find win-win solutions for city resilience.
Cities are considered particularly vulnerable to the impacts of climate change. This stems from their high concentration of activities, assets and people, and as buildings and infrastructure were not designed with future projections of climate in mind. Residents are also particularly vulnerable due to the Urban Heat Island (UHI) effect, whereby temperatures are higher than in surrounding rural areas due to the heat storage of paved and built up areas, reduced radiative cooling, and waste heat from buildings, transport, and industry.
Many cities, such as London, have taken the lead on developing adaptation strategies to enhance the resilience of the built environment and infrastructure to future climate risks. There has been a lot of focus on climate risk, impacts and potential solutions at a sectoral level. This was the approach taken in the previous UK Climate Change Risk Assessment, and is an approach that is often used in the development of city adaptation strategies both nationally and internationally. However, this approach can overlook wider implications of impacts and adaptation, such as opportunities and trade-offs with other sectors. For example, increased uptake of air conditioning in commercial offices can reduce risks of thermal discomfort but will also enhance the UHI effect and the risk of high temperatures to other sectors, including residential housing and transport.
Furthermore, adaptation to climate change is not the only factor driving the future form of the built environment and infrastructure systems. This will also be shaped by a host of different economic and policy drivers. All these factors are expected to change in the future, in ways which are not necessarily independent of one another. Improving our understanding of these interactions and interdependencies can help provide cities with better information to develop more sustainable adaptation strategies.
A practical approach to this is through the use of Integrated Assessment Modelling. This allows multiple models, analysing different components of cities and scenarios of long term change such as the climate, economy, land-use, and transport systems, to be coupled together to provide a more comprehensive analysis of the city as a system. This approach has been demonstrated through the ARCADIA project, which developed a new system of models and integrated them within the Urban Integrated Assessment Framework (UIAF).
Outputs from the different component models interact and feed into the impact and adaptation assessment model. This allows multiple climate risks, cross-sectoral impacts, and adaptation options to be analysed in a single framework. For example, we have investigated the economic effects of high temperatures on the functioning of the railway system, consequential economic and social impacts on commuter delays and disruption, and the resultant indirect economic impacts this has on labour productivity and the wider economy. We have also investigated the impact of high temperatures in residential buildings for thermal comfort and mortality risk. This highlighted the importance of mainstreaming adaptation across different policy areas, such as health and urban planning, and highlights potential benefits of adaptation which may cross policy areas to provide win-win situations.
Other benefits of using an integrated approach include the ability to couple additional models or data sets to support the impact and adaptation assessment. For example, London Underground provided platform temperature sensor data which could be used to infer external to internal temperatures, as well as outputs from a passenger thermal comfort model. We used outputs from the spatial urban Weather Generator to provide a risk based analysis of the future number of days when passengers travelling on sections of the Tube could be subjected to thermal discomfort under future scenarios of climate change, the potential number of passengers dissatisfied, and the role of air conditioning in reducing this risk.
However, while significant advances have been made, challenges still remain if we are to create stronger links between these modelling activities and the decision making process. Wise et al., report that this link is difficult as decision-makers need to assess and prioritise a range of options whilst considering:
- interconnected systems
- barriers related to human behaviour and governance
- differences in vulnerability and preferences of populations
- cross-scale effects over space and time
- multiple forms of uncertainty.
Consequently, the focus is now on adaptation pathways approaches which provide a method to visualise and appraise different strategies whilst considering the adaptive nature of the decision process, the complexity of the problem, and future uncertainties. This will require a more decision-orientated approach to modelling climate risks and adaptation. As such, urban integrated assessment models, like the UIAF developed in the ARCADIA research project, need to continue to be progressive in their development and reflect the changing needs and demands of decision makers to reach their full potential.