Does infill outperform climate-adaptive growth policies in meeting sustainable urbanization goals? A scenario-based study in California, USA

Land allocation for urban growth is central to sustainable development strategy because urban growth can impact space available for food production, ecosystem services and biodiversity conservation. Urbanization is a growing stressor due the 2.5 billion additional people projected to live in urban areas by 2050. Potential climate change impacts to natural systems increase the need for sustainable urbanization, which should integrate land use needs for urban growth with climate adaptation objectives such as maintaining biodiversity, food production and ecosystem services. Here we compare climate-neutral and climate-adaptive urbanization scenarios to see which produces the most sustainable urbanization, defined as being the most effective at meeting development, conservation, and two climate adaptation objectives. We modeled five urban growth scenarios portraying an increase of 25.8 million people by 2050 for California, USA comprising three climate-neutral scenarios: business-as-usual, compact-new-growth and infill (redevelopment); and two climate-adaptive scenarios: preservation of agricultural climate refugia or future plant dispersal corridors. Infill was the least impacting for the multiple objectives tested; preserving 46-57% more land for other uses. Each climate-adaptive scenario reduced land consumption for its respective target, but increased impacts to the opposite climate-adaptive scenario target. Infill has the potential to contribute towards sustainable urbanization, particularly if combined with other climate adaptation targets.