Melbourne’s busiest day is Thursday, Sydneysiders are hardest at it on a Friday while Sunday commonly appears to be a day of rest, according to a new analysis of city temperatures.

The new research, led by the University of Melbourne, investigated temperatures in some of Australia’s major cities to reveal a fascinating insight into just how human activity affects the urban environment.

Dr Nick Earl and Professor Ian Simmonds from the University’s School of Earth Sciences, along with Professor Nigel Tapper from Monash University, are interested in identifying weekly cycles in nature.

Doing so proves an anthropogenic influence since nothing in nature conforms to a weekly pattern.

They analysed surface temperature data dating as far back as 1943 from seven of Australia’s major cities, including Melbourne, Sydney, Brisbane, Perth, Adelaide, Hobart and Cairns.

Canberra was left out because its meteorological station has moved too many times and Darwin’s was too far removed from the city centre.

The study showed that weekly cycles in daytime temperatures occur in almost all of the tested cities, with the strongest signals in those with bigger populations, such as Sydney and Melbourne.

Early mornings versus the afternoon also gave more statistically significant results.

Among the interesting findings:

  • Testing temperatures at 9am delivered the firmest signals, with both Brisbane and Melbourne’s weekly cycle peaking on a Thursday, with a Sunday minimum
  • Sydney peaks on a Friday, also with a Sunday minimum
  • There are two peaks in daytime temperature during the working week, typically between 7-9am and 4-7pm
  • Comparing 9am (daytime) and midnight (nighttime) temperatures, weekends were significantly warmer than weekdays

 

Professor Simmonds said the study could prove valuable as cities move towards more sustainable living by demonstrating how our behaviour affects the city we live in.

“It’s really a peek into the weekly routines of Australia’s big-city dwellers,” he said.

“Generating electricity, driving cars and using air conditioning and heaters all deposit waste heat into the atmosphere and it shows in the city temperature.”

While a weekly pattern was not evident in all cities or for all tested times, Professor Simmonds said it was possible other factors were clouding the pattern.

Sydney, for example, didn’t have warmer weekend nights like Melbourne or Brisbane, which the authors suggest could have to do with its location well above sea level.

The study also compared the temperature recordings to traffic levels, showing a clear correlation between reduced traffic and lower temperatures.

Mornings were also generally warmer than the afternoons, with mornings more often associated with atmospheric inversions which can trap waste heat near the surface.

By contrast, by the afternoon such inversions have evaporated, thereby carrying heat away to higher levels.

The impact of Melburnians on their city was another focus of the study, with its ‘urban heat island’ effect analysed for a weekly pattern.

The ‘urban heat island’ or UHI refers to the well-established reality that cities having higher temperatures than surrounding areas (in Melbourne’s case, Tullamarine, Laverton and Moorabbin).

Melbourne’s UHI peaks between 9pm and midnight, highlighting the biggest contrast in activity while the difference is least significant between 9am and 3pm.