City form and natural process - indicators for the ecological performance of urban areas and their application to Merseyside, UK

It is well known that urbanisation has many deleterious ecological effects. These may be mitigated by good urban design but the first step in doing this is to quantify them. This paper describes four simple ecological performance indicators which quantify the effects of urbanisation on surface temperature, hydrology, carbon storage and sequestration, and biodiversity. They have been developed and customised from recent studies, are simple to use, and require a minimum of input information; the only major inputs needed are the percentages of the different surface covers. The indicators were tested by applying them to four urban areas of Merseyside, UK, of contrasting affluence. The results showed that the greatest influence on ecological performance was the percentage of greenspace, particularly of trees. The affluent areas had lower temperatures, less run-off, more stored carbon, and higher diversity, largely because they had more open area and woodland cover. These results suggest that the indicators could be a useful planning tool, facilitating the comparison of existing urban areas, and helping to predict the ecological impact of new developments. However, the indicators also suggest that compact cities with good regional performance will inevitably have poorer performance locally, because of a lack of greenspace. The performance indicators could determine the potential of possible means of amelioration such as the use of roof gardens or permeable paving. (C) 2001 Elsevier Science B.V. All rights reserved.