8/13/2019 Global urban expansion

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S H L O M O A N G E L M A K I N G R O O M F O R A P L A N E T O F C I T I E S 39

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The Dimensions of GlobalUrban Expansion, 20002050

The third attribute of urban expan-sion discussed in this report is theincrease in urban land cover. Accra,the capital of Ghana, offers a star-

tling example (gure 4.1). Between 1985 and2000, the citys population grew from 1.8 to2.7 million, a 50 percent increase, while its

urban land cover expanded from 13,000to 33,000 hectares, a 153 percent increase.Urban land cover in Accra grew more thantwice as fast as its population. We examined the growth rates of theurban population and the urban land coverin the global sample of 120 cities between1990 and 2000. Population growth averaged1.60 percent per annum, and land covergrowth averaged 3.66 percent per annum.The difference between them was 2.06 per-

cent. Thus, as in Accra, urban land coverin all 120 cities grew on average at morethan double the growth rate of the urbanpopulation. At these rates, the worlds urbanpopulation will double in 43 years and theworlds urban land cover will double inonly 19 years. The rapid growth of urban land coveris by no means a recent phenomenon, asclearly shown in the historical expansionof Bangkok, the capital of Thailand, duringthe past 150 years (gure 4.2). Bangkok in-creased its urbanized area from 580 hectaresin 1850 to 133,515 hectares in 2002. In 1944,for example, its urbanized area comprised8,345 hectares, a 14-fold increase over its1850 area. The city then doubled its areain 15 years (19441959), doubled it again in9 years (19591968), doubled it again in 10

years (19681978), and doubled it yet againin 24 years (19782002). In other words, theurbanized area of Bangkok increased 16-fold between 1944 and 2002, at an average

FIGURE 4.1

Expansion of the Built-up Area of Accra, Ghana,19852000

growth rate of 4.8 percent per annum. When we examined the growth ratesof urban populations and their associatedurban land covers in the representativeglobal sample of 30 cities between 1800 and2000, we found the rates in Bangkok werenot atypical: 28 of the 30 cities studied in-creased their areas more than 16-fold duringthe twentieth century. The only exceptionswere London and Paris, the two largest citiesin the sample in 1900. These two cities hadincreased their areas 16-fold since 1874and 1887 respectively.

On average, the 30 cities in the represen-tative sample doubled their urbanized area

Urban built-up area

Suburban built-up area

Rural built-up area

Urbanized open space

Rural open space

Study area

Water

No data

Centralbusinessdistrict

1985

2000