4. Canberra’s growing urban area

4.1 Impacts of urban growth

Did you know that it’s much more sustainable to live in a compact city than one that is spread out?

Cities put pressure on the environment. The more land they use, the greater this pressure grows. Expanding our cities by building new suburbs on the urban edge has a range of negative impacts on biodiversityThe variety of all life and living processes in the environment., waterway health and greenhouse gasA gas in the atmosphere (such as carbon dioxide, methane and nitrous oxide) that absorbs and emits energy, warming the Earth. Greenhouse gas emissions from human activities are the main cause of climate change. emissions.

Let’s look at these impacts in more detail.

Impacts on biodiversity

Clearing land to build new suburbs destroys and fragments habitats. Lots of land being cleared in the ACT contains old eucalypt trees, which have hollows that provide important habitat for native species. Habitats that do survive are often isolated. Structures like roads divide habitats up into small, disconnected patches which makes it difficult for animals to migrate, breed and hunt successfully.

Even once they are built, suburbs on the urban edge have ongoing impacts on the surrounding environment. Light and noise pollution from streets and houses disrupt animal behaviour, and temperatures can rise due to the urban heat island effectThe phenomenon of urban areas experiencing much higher temperatures than surrounding rural and natural areas. This is because urban areas have less greenspace and more hard surfaces that absorb and retain heat - like buildings, footpaths and roads.. Backyard weeds can spread to nearby reserves, and pets like cats can hunt native wildlife. Collectively, roaming pet cats kill 546 million animals per year in Australia!

Impacts on waterways

Simply changing an area of land from natural to urban creates unavoidable negative impacts on water quality. Urban areas are mostly made of hard, unnatural surfaces like concrete and asphalt, which don’t let water through. When rain falls on roads, roofs and footpaths, it picks up pollutants and quickly carries them downstream. Harmful pollutants in urban areas include chemical fertilisers, pet poo, lawn clippings, oil, heavy metals, and even decomposing leaves. All of these can impact aquatic ecosystemsA biological community of interacting living and non-living things.. In contrast, when rain falls in natural areas, most of it is absorbed into the soil and gets filtered before it seeps into rivers or groundwater. Additionally, water travels much more quickly through concrete channels than natural ones, which increases the risk of flooding and erosion downstream.

Impacts on greenhouse gas emissions

As our urban area increases, so do the greenhouse gasA gas in the atmosphere (such as carbon dioxide, methane and nitrous oxide) that absorbs and emits energy, warming the Earth. Greenhouse gas emissions from human activities are the main cause of climate change. emissions from transport. When suburbs are spread out, people tend to drive their cars more than in areas like city centres where things are closer together. If you live far away from where you work, go to school or do your hobbies, it’s much harder to walk or ride your bike to get there. Public transport options are often more limited the further you get from city centres as well.