With half of the world’s population living in cities, and the proportion increasing, addressing the greenhouse gas emissions from cities on future levels of climate change, and of the effects of climate change on cities, is increasingly relevant.
Hunt and Watkiss summarise the current evidence for climate impacts and adaptations at the city level, evaluating whether the benefits of city-level analysis are being fully realised. They focus on studies where quantitative economic analysis of climate change risks has been included, and find that the impact of rising sea levels and river floods, clean water availability and health risks have most often been considered, while impacts on the key sectors of energy, transport and infrastructure are least studied. Most studies suggest that climate change influences are significant enough to be part of medium-to-long term decision making on development and infrastructure.
Hunt, A. and Watkiss, P., 2011. Climate change impacts and adaptation in cities: a review of the literature. Climatic Change, 104 (1), pp. 13-49. Available at: http://dx.doi.org/10.1007/s10584-010-9975-6
The cities that are most advanced in developing assessments and responses to climate related risks have benefited from involving stakeholders at an early stage in the risk assessments, incorporating climate change considerations formally into planning frameworks and allocating responsibility for climate change issues to a designated group. A key benefit is that focus at this local scale aligns more closely with many decision making and funding decisions as well as making the risks and opportunities more meaningful to individuals.
Impacts of climate change on cities
Larger cities, close to water, and economically dependent on weather related sectors are most at risk from climate change. As a result the majority of quantitative studies focus on coastal cities or those next to major rivers. Most studies focus on a single climate risk, that most frequently being rising sea levels, perhaps due to the greater existing understanding of this.
Many major cities are in coastal areas, where rising sea levels and storm surge risk could cause flooding, land erosion, infrastructure damage, human displacement, and reduced access to drinking water. The physical impacts and related costs of sea level rise have been widely studied, though mainly at an aggregate or country scale, with cost-benefit analyses undertaken to compare the merits of different adaptation approaches, such as defending land against flooding or living with more inundation. Where city level analysis has taken place, it has focused on cities with high value assets to protect (such as economic centres, infrastructure and tourism) rather than those at highest risk (which are typically in developing countries, due to the lack of existing protection).
Buildings and infrastructure are at risk from climate related extreme events, such as storms and storm surges (with the “costliest” weather events in the developed world). Most research in this area has been undertaken by insurance companies, who have an interest in quantifying future risk profiles and the future costs of storms. An emerging body of research examines the impact of extreme weather on cities with a view to evaluating the broader economic costs, since disruption in major cities is likely to have knock-on effects in other parts of the country, e.g. transport disruption.
Energy demand is expected to increase with the higher temperatures associated with climate change and demand for cooling, but with reduced demand for heating in colder countries/periods, though the degree to which they offset each other will vary by region. In large cities the cooling demand can also be further exacerbated by the urban heat island effect (the city ‘microclimate’ brought about by the concentration of buildings and man-made surfaces). However, quantifying future energy demand is complicated by uncertainties around the emergence and cost of new technologies, underlying income levels, and the adoption of alternatives to current energy use as part of mitigation responses.
Health impacts include the direct effects of heat and cold on people, as well as the indirect effects of changes in disease patterns. There is a high degree of variation in health impacts with the effects of heat are likely to be most important in developed country cities, particularly those that experience heat extremes, while evolving disease patterns are thought to be the highest risk for developing countries.
A changing climate may impact the demand, availability (supply) and quality of water. There are few studies on the impact and possible responses to reduced water availability at the city scale since the assessment of water availability typically needs hydrological information collated on a larger scale. However this is changing as cities are recognising the need to evaluate existing water resources, and a greater focus on short term adaptation strategies is needed. A key difficulty in interpreting climate model information for this risk is the unpredictability in regional and seasonal rainfall.
Current city-level analysis
The most in-depth studies quantifying climate change impacts at a city level have focussed on major cities in the UK, USA, Scandinavia and New Zealand, reflecting the availability of funding and dedicated organisational structures to tackle the issues. Historically climate studies have tended to be qualitative, due to the difficulty in obtaining reliable and comparable quantitative data, but that is changing, starting with evaluating economic cost in areas where the impact of climate change is felt by markets. In London and New York the involvement of key stakeholders was key to developing the research, focussing the research on the issues of most concern to them, and to communicating it to other interested parties.
The sectors most focussed on are also those that are currently under pressure from growing populations and demand for resources. In London the transport infrastructure, flood risk and health effects of heat waves were prioritised, while in New York health and water resources were previously seen as most critical (though Hurricane Sandy changed this). The initial scenario analysis was qualitative, followed by quantitative estimates of physical impacts and economic cost of adaptation. The authors identify a number of key areas where more research is needed, including evaluation of cross-sectoral impacts and adaptation as well as management of major catastrophes.
Conclusions and recommendations
Studying climate change impacts at a city level reflects a trend towards considering climate change at a more local level. Three key drivers are: that climate modelling is becoming more sophisticated and allowing more granular scenario analysis; that cities play a key role in social and economic activities, and that adaptation decisions are local and thus the city level is often the appropriate scale for decisions and responses.
In addition, the authors suggest that a standardised impact/adaptation methodology would aid comparison between cities as well as support localisation by focusing limited resources on critical areas, in particular identifying where adaptation lessons can be shared between similar cities. Although the most vulnerable cities are found in developing countries, these cities are affected most by lack of resources to understand and adapt to climate change risks.
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RI Quarterly Vol. 4: Focus on climate
RI Quarterly Vol. 4: Focus on climate
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Climate change impacts and adaptation in cities