Weekly cycle of meteorological variations in Melbourne and the role of pollution and anthropogenic heat release

An aspect of anthropogenic impacts on climate have been assessed by examining the day-of-the-week variation (DOWV) of important meteorological elements. The data used were those of daily maximum and minimum temperature and rainfall for Melbourne for the period 1856–1990. This long series has been broken up into five 27-yr subperiods to expose how any such variation has changed over the record. We find there to be no DOWV in the summer “half” of the year for any of the subperiods. The only statistically significant variations to have physical meaning occur in the winter of the most recent subperiod (1964–1990). In that time maximum temperature exhibits a significant (10% confidence level) DOWV and weekdays are 0.29°C warmer than weekends (5%). Minimum temperatures and rainfall amounts were also found to be greater (10% level) on weekdays by 0.24°C and 0.20 mm d−1, respectively. We have considered the possible impacts of day-of-the-week variation of atmospheric pollution loading and of the local generation of heat. We hypothesise that the magnitude of the contrast between weekday-weekend anthropogenic heat emissions is sufficient to explain the temperature differences and these in turn are consistent with the weekday excess of rainfall. This perspective is concordant with the results of many recent studies which stress the importance of anthropogenic heating.