Making cities sustainable under climate change

In order to enable cities to adapt to climate change, built environment professionals need an understanding of how climate change will affect cities. In a new ICE paper, Climate change and growing megacities: hazards and vulnerability (2017), leading academics from University College London and Arizona State University, discuss the outcome of their research on the potential impact of climate change for three different types of megacities: for cities in deserts, for Asian and subtropical cities, and hazard amplification.

For cities in deserts, increased cooling demand may increase the occurrence of peak electricity loads that coincide with the times when electricity generation efficiencies are lowest, as well as transmission line cooling being prevented by low wind speeds or high night-time temperatures.

For Asian and subtropical cities, climate change and air pollution interact in several complex ways. For instance, air pollution can further reduce very low winter temperatures by blocking solar radiation, but in summer, increased use of air conditioning can exacerbate the production of air pollutants in the short term, and increased climate change in the longer term, especially in the lengthy periods of calm conditions that are now predicted.

Lastly, climate change will amplify many of the hazards cities already face. For instance, although wind speeds can be reduced over cities, at local level turbulent gusts of wind will be much greater under climate change, making the risks from tropical cyclones and tornadoes even greater. The increased risk from hydrological extremes (droughts and floods) means that urban design strategies need to include man-made rivers, reservoirs and planned flood areas. In these, engineered infrastructure resilience is a potential adaptive mechanism.

Air pollution in cities under climate change

In 'Modelling impact of climate change and air pollution in cities' (2017), Lu et al describe a new model with 12 indices for investigating urban air pollution and climate change. The 'driver-pressure-state-impact-response' model includes the indices of population, enterprise, registered vehicles, energy consumption, emissions and concentrations of carbon dioxide and sulfur dioxide, land-use change, annual temperature, tropical nights and reforestation. The model clearly illustrates the systemic interaction between the various drivers of air pollution and will be an important tool for city policy makers in China.

Building underground in cities, sustainably

Increasing urbanisation is placing huge pressures on land-use within cities while increasing demand for infrastructure and services. One response to this challenge is to develop infrastructures below ground. Sustainability indicators and accreditation standards have been developed for the built environment above ground. In their paper, 'A new sustainability framework for urban underground space' (2017), Zargarian et al propose a new framework for the sustainability of underground urban space. They evaluate a range of existing sustainability frameworks before using a Sustainable Project Appraisal Routine framework as the basis, specifically designed for underground space projects.

Adaptable housing design for climate change

In a new paper by Kinnane et al, titled 'Adaptable housing design for climate change adaptation', the researchers evaluate the present and likely future performance of a novel house design using cold-framed, light gauge steel wall modules with screw fixings. The house has a novel 'adaptable' design so that 'layers, site, form, structure, envelope, services and internal spaces' can be modified as the climate changes. Insulation thickness was beyond current regulations. Even for this novel design, one result is familiar: a 'performance gap' in current energy consumption of 40% greater actual demand than simulated demand.

However, the overheating responses of the building in future hot summers are novel and very useful for practitioners. Two measures had little effect in reducing overheating: high level of wall insulation and internal drapes. Even worse, the addition of an extension to the building increased the number of overheating periods. However, the addition of external solar shading over glazed areas (louvers, east-side flaps) reduced predicted overheating hours by 25% even in the hot summers predicted for 2080. Incorporating these lessons into new building design will enable the construction and development of the most climate-adaptive buildings.

Built environment collaboration will enable innovation.

These ahead-of-print articles show how innovative structures can enable cities to respond effectively to climate change. Collaboration across the whole built environment sector will enable such innovative responses to thrive.