Population and land cover projections under greyfield development: implications for densification, urban forest, water performance, and heat

We modelled the change in housing stock associated with greyfield redevelopment as the main urban densification strategy in Australian cities. First, an integrated city model was developed by linking spatial databases that represent existing land cover, urban form, socio-demographics, and urban planning regulations (zoning and building codes). Then, by considering alternative urban design typologies and population projections, the model simulated business-as-usual greyfield infill redevelopment for different time horizons up to 2051. We found that this development alone would not create sufficient additional housing to meet the growing population and densification targets. The gap in 2051 is expected to be 264,280 people, or 26 % of the current city's population. The model also allowed us to project changes in the biophysical attributes of the city caused by infill. Impervious surfaces were projected to increase by 6.63 ± 1.67 km², while tree cover on private land was projected to decrease by 3.43 ± 0.87 km². The area of private greenspace was anticipated to reduce by 0.95 ± 0.14 km², a decrease in urban forest of 2 m² per person by 2051. This change would result in more stormwater runoff and demand for potable water, higher investment in infrastructure for drainage, water supply and wastewater services. The loss of greenspace would negatively impact the urban heat performance of the city. The result emphasises the need to consider alternative approaches to densification by revealing the current inefficiencies in meeting the housing demands of the growing population and the associated risk of cities' biophysical degradation.