Cities

city’s electricity demand. A biomass CHP system and wind turbines provide for a further 1.3 per cent and 6 per cent respectively of the city’s energy needs (IEA 2009).

Oslo and São Paulo have harnessed power generated by nearby hydro-electric facilities to gain a relatively high share of renewable energy. Wind and tidal power are becoming increasingly important sources of renewable energy for cities, while geothermal heat can also be exploited to provide reliable, secure, low-cost, power. Manila, located on the island of Luzon, receives 7 per cent of its electricity from geothermal sources (ICLEI, UNEP and UN Habitat 2009). A grid-based, decentralised energy system, with district heating systems can provide space and water heating for large urban complexes (like hospitals, schools or universities) or residential neighbourhoods. They can significantly reduce overall energy demand. Their efficiency further improves with combined heat and power energy generation systems. Copenhagen‘s district heating system, for example, supplies 97 per cent of the City with waste heat (C40 Cities 2010d).

4.4 Vegetation and landscape

While cities are principally made up of buildings and infrastructure, they can contain a significant proportion of open space. Despite sustained growth, cities like Johannesburg, London and Delhi have maintained high levels of green open space (parks, public and private gardens), while others like Cairo, Tokyo or Mexico City have far lower levels of green space. Parks, protected green space and gardens, street trees and landscaping provide vital ecosystem services, acting as green lungs absorbing and filtering air pollution or as acting as filters for waste water (TEEB 2010). They also provide a habitat for wildlife and offer recreational benefits to city dwellers.10 As noted above, a study of Toronto’s Greenbelt identified its wetland and forests as one of its most valuable assets in terms of ecosystem services including carbon storage, habitat, water regulation and filtration, flood control, waste treatment and recreation (Wilson 2008).

In addition, the presence of green landscaped areas helps regulate natural processes, including the mitigation of local temperature extremes: a ten per cent increase in tree cover reduces cooling and heating energy use by between five per cent and ten per cent (McPherson et al. 1994). Vegetation and soft open space also play a role in decreasing stormwater volumes, thus helping cities to manage the consequences of heavy rainfall, and are

10. At the macro level, strategies for greening the city protect existing green areas from development. Such measures are of particular importance along the city fringe, where urban growth boundaries in cities such as Portland and London restrict development. In Stockholm, thanks to the protection of green areas, almost the entire population lives within 300 meters of parks and green areas (City of Stockholm 2009).

effective in helping flood protection in coastal cities. New design strategies have pioneered the use of green roofs and facades on buildings, to add to the quantity of natural (as opposed to man-made) surfaces in cities and to reduce cooling energy demand. For example, Itabashi City in Tokyo is promoting climbing plants as “green curtains” around public buildings and private homes to avoid buildings overheating in summer and to reduce the use of air conditioning (ICLEI 2009b).

4.5 Water

Cities require significant transfers of water from rural to urban areas with water leakage being a major concern. Upgrading and replacement of pipes has contributed to net savings of 20 per cent of potable water in many industrialised cities. Over the last ten years alone, Tokyo’s new water system has reduced water waste by 50 per cent (C40 Cities 2010e). Volumetric charging has proven most effective in incentivising more efficient water use. Many cities are introducing water meters and are shifting away from simple water access fees. A measure to maximise utility of fresh water is the cascading of water use where the waste water generated by one process can be used in another with a lesser quality requirement (Agudelo et al. 2009).

To further reduce water consumption and provide alternatives to piped water supply, rain can be harvested and used as drinking and non-drinking water. Such services can only be implemented in cities where there is a greater willingness to pay for water than in rural areas (see Water Chapter). To counter severe water shortages in Delhi, the Municipal Corporation made rainwater harvesting a requirement for all buildings with a roof area above 100 square metres and a plot area greater than 1,000 square metres. It is estimated that 76,500 million litres of water per year will be made available for groundwater recharge (ICLEI, UNEP and UN-HABITAT 2009). In Chennai, urban groundwater recharging raised the city’s groundwater levels by four metres between 1988 and 2002 (Sakthivadivel 2007). Fiscal incentives have proved successful, notably Austin’s tax rebates for harvesting systems saving an estimated 8.7 gallons per person per day for a single family rainwater harvesting unit (Texas Water Development Board and GDS Associates 2002).

4.6 Food

The food footprint of a city has significant impacts on its green credentials, especially if one takes into account the energy use generated by transporting food from remote locations to urban marketplaces (Garnett 1996). For example, the food supply of European

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