If you can’t stand the heat, get out of the city

Research conducted by the University of New South Wales (UNSW) and the ARC Centre of Excellence for Climate System Science has found that an expansion of concrete and asphalt on the fringes of our cities could see urban temperatures rise by as much as 3.7°C by the year 2050. The study has been published in the journal Climate Dynamics.

The researchers used the Weather Research and Forecasting Model to simulate present (1990-2009) and future (2040-2059) climates in the Sydney area. The future simulation incorporated projected changes to account for expected urban expansion.

“The analysis of the temperature changes revealed that future urbanisation will strongly affect minimum temperature,” the researchers found.

“The minimum temperature changes will be noticeable throughout the year. However, during winter and spring these differences will be particularly large.”

The researchers say the build-up of heat in cities is due to the ‘urban heat island effect’, which will amplify climate change. The effect occurs because urban structures can store more heat than open ground. This accumulated heat is released during the night, meaning night-time temperatures will increase even more than daytime temperatures.

Lead author Dr Daniel Argueso noted that this increase “has implications for health problems related to heat stress accumulation and at an economic level where the higher energy consumption needed to power air conditioning overnight may lead to higher power bills.”

Urban surfaces also hinder evaporation and its cooling effect, adding another layer to the heating of urban areas. So green spaces, trees and bodies of water are important design features to reduce the heat effect, said Dr Paul Osmond.

“Not only do these help keep suburbs cooler, there is also a knock-on effect where these places gain social advantages through additional amenities and recreational areas. Quite often, leafy suburbs that contain a number of parks and bodies of water also tend to see increased real-estate values. It’s a win-win situation for everyone.”

If nothing is done, new areas on the fringes of Sydney could see temperatures rise between 1.1-3.7°C, while the rural areas near these new suburbs could see increases of 0.8-2.6°C. Existing urban areas closer to the CBD will see rises of 1.1-2.5°C.

Areas closer to the CBD of major cities are not exempt from the temperature rises - density, in particular vertical expansion, plays an important role in the urban heat island effect. So as global warming develops, urban designers will have to consider ways to ease the heat increase.

The Sydney-focused research has lessons for cities right across Australia. But Australia’s regional climatic variability means scientists will need to extend their research to other cities to better understand their climatic characteristics and get a more comprehensive understanding of urban impacts on local temperature.

“We need to develop a complete profile of temperature changes for different cities, taking into account their various urban expansion prospects and locations,” Dr Argueso said.

“With this information, we can provide an invaluable tool to help with the future development of Australian cities and the environment many of us live in.”