Cities and Climate Change
Climate change and its ramifications on urban processes cover a wide spectrum. Climate-related natural disasters are increasing in frequency and magnitude. Their consequences will depend on a number of factors, including the resilience and vulnerability of people and places.
Climate conditions have always shaped the built environment. Since the 1950s, however, traditional patterns adapted to local climatic conditions have been increasingly abandoned. Globalization and rapid technological developments tend to promote homogenized architectural and urban design, regardless of natural conditions. With this cookie-cutter architecture comes increased energy consumption from the transportation of exogenous materials and from the utilization of a single building design in a variety of environments and climatic conditions without regard to its energy efficiency. In some places, energy is too cheap to motivate energy-efficient design; in other cases, developers ignore the costs, since sale prices do not reflect the future savings from higher energy efficiency.
The use of new architectural and urban forms, new materials and innovations such as air conditioning have driven up both energy costs and cities’ contributions to greenhouse gas emissions. Technological advances have also permitted the rapid growth of cities in places previously considered uninhabitable. For instance, the American city of Phoenix has boomed thanks to engineering projects that diverted water from the Colorado River; city water in the Saudi Arabian city of Riyadh comes largely from desalinization plants.
Urban form and function also help define the nature of the interactions between cities and local climate change. For example, the “urban heat island effect” results from the impacts of different land uses in urban areas, creating microclimates and health consequences.
The urban heat island effect is an increase in temperatures in the urban core compared to surrounding areas. The size of the urban centre, the type of urbanization, urban form, function and land use all contribute to the effect. As villages grow into towns and then into cities, their average temperature increases 2 to 6°C above that of the surrounding countryside.(12)
Urban designs and forms that neglect local climatic conditions and lose the cooling effects of green areas tend to aggravate the heat island effect. Cities of poor countries in the tropics are particularly affected.
Rapid urban growth, combined with the potent impacts of climate variability and climate change, will probably have severe consequences for environmental health in the tropics (causing, for example, heat stress and the build-up of tropospheric ozone), which can affect the urban economy (for example, yield of labour and economic activities) and social organization.
In a vicious circle, climate change will increase energy demand for air conditioning in urban areas and contribute to the urban heat island effect through heat pollution. Heat pollution, smog and ground-level ozone are not just urban phenomena; they also affect surrounding rural areas, reducing agricultural yields,(13)increasing health risks(14)and spawning tornadoes and thunderstorms.
Human health in urban areas may suffer as a result of climate change, especially in poor urban areas whose inhabitants are least able to adapt. They already suffer from a variety of problems associated with poverty and inequity. Climate change will aggravate these. For example, poor areas that lack health and other services, combined with crowded living conditions, poor water supply and inadequate sanitation, are ideal for spreading respiratory and intestinal conditions, and for breeding mosquitoes and other vectors of tropical diseases such as malaria, dengue and yellow fever. Changes in temperature and precipitation can spread disease in previously unaffected areas and encourage it in areas already affected. Changes in climate and the water cycle could affect water supply, water distribution and water quality in urban areas, with important consequences for water-borne diseases.
The impacts of climate change on urban water supplies are likely to be dramatic. Many poor countries already face accumulated deficiencies in water supply, distribution and quality, but climate change is likely to increase their difficulties. The recent report of the Inter-governmental Panel on Climate Change underlines that cities in drier regions, such as Karachi in Pakistan and New Delhi in India, will be particularly hard hit.(15)