The future is smaller
The researchers separated the 60 cities into four categories according to their 2015 populations: very large (2.5 million or more inhabitants); large (more than one million); medium-large (between 500,000 and one million) and medium (between 96,000 and 500,000), with an equal distribution of cities with and without greenbelts. They quantified urban sprawl using a metric called weighted urban proliferation (WUP). It assigns a value to urban sprawl based on the amount of built-up areas in a landscape, how dispersed those areas are and the average amount of land taken up per inhabitant or job.
They examined the sizes of target cities’ built-up areas in 2006 and 2015, the longest time frame possible given the available data. While cities both with and without greenbelts showed increases in built-up areas, says Pourtaherian, “the differences between them were mainly due to land uptake per person, meaning the area that an individual occupies on average. In cities with greenbelts, the decrease in land uptake per person was the most effective measurement that led to a decrease in urban sprawl.”
Overall, 90 per cent of cities with greenbelts experienced decreases in urban sprawl. In contrast, just over a third — 36.7 per cent — of cities without them saw their sprawl decrease. Much of that decrease is the result of denser development, with lower uptake per inhabitant.