A question of sustainability or survival?
Climate change poses a serious threat to the long-term habitability of planet earth. This existential crisis for humanity will play out differently across a variety of battlefronts. Some areas will suffer most from sea level rise, some from extreme rainfall and flooding, but for Australian cities the major risks are water scarcity and heat.
During the millennium drought parks and private gardens in Melbourne suffered severely from water restrictions, turning a green city distinctly brown. It is easy to forget how close Melbourne came to disastrously running out of water, as is currently occurring in Cape Town, South Africa.
Heatwaves cause more deaths in Australia than any other natural disasters. During the Black Saturday bush fires, more people died from the heatwave in Melbourne than died from the fires.
Of course, water scarcity and heat are not independent phenomena. Not only does hot weather often coincide with dry weather, and lead to increased water demand, but also intelligent water management may end up being one of our best defences against heat.
Adapting to water scarcity
Water scarcity is primarily caused by population growth, short-term droughts, and long-term changes to rainfall averages. Fortunately for our cities, humans are no longer entirely dependent upon rainfall for water resources.
All major cities in Australia have constructed desalination plants, and all have made some attempts towards wastewater recycling. Desalination technologies are condemned by some as altogether unsustainable due to energy usage.
Wastewater recycling for non-potable uses, such as agriculture, parks, gardens, toilets and laundry, is a viable option in some specific circumstances, but generally does little for a city’s overall water balance.
Recycling wastewater into drinking water supplies allows far more water to be recycled, but faces challenges with community perceptions of safety. This approach has been adopted in Singapore since 2002, and will soon be the case in San Diego, where it will supply a third of the city’s water demand.
Urban areas suffer from a phenomenon known as the Heat Island Effect, which is caused by replacing vegetated areas that naturally shade and cool, with unshaded asphalt and concrete and other materials which retain heat. When combined with the expected temperature increases associated with climate change, we can expect urban heat to be an increasingly dire issue into the future.
Fortunately, there are a variety of strategies our cities can adopt to ameliorate these risks. Planning regulations can be used to ensure buildings are designed for hot weather. Unnecessary hard surfaces can be ripped up and replaced with vegetation. Street trees, green-walls and green-roofs can be used to provide as much shade and evapotranspiration as possible. Already existing green spaces can have vastly more trees planted, such as the 1 Million Trees project by the Greening the West group which is nearing completion in Melbourne’s west.
However even tree planting is not free of controversy. Native trees provide better outcomes for biodiversity, and survive better without watering, but exotics have more ability to reduce urban temperatures through shade and evapotranspiration.
Due to uncertainties around climate change temperature and rainfall impacts in the future, there is some risk that large proportions of Melbourne’s greenery, even native species, will die off unless we can provide additional water for irrigation.
A question of sustainability or survival?
Recycling wastewater into drinking water supplies is another viable alternative, but requires proactive campaigns to shift public opinion, rather than listening to what the community currently wants.
Planting of exotic trees would do more towards the reduction of urban heat, but require more water, and provide far less benefits for biodiversity.
At this point in history in many places we have the luxury of debating such trade-offs, but the real risk is that in the future the conversation may change from a question of long-term sustainability towards a question of medium-term survival.
Urban inhabitants can help deal with water scarcity and heat through conserving water, and adapting homes to be more resilient to heat through measures such as eves, shading, insulation, and trees around windows. Those seeking to make a more significant contribution could consider participation in a community group that actively conducts tree planting, such as the Friends of Lower Kororoit Creek.
Dr Casey Furlong, Post-doctoral Research Fellow, Centre for Urban Research, RMIT