Moruya Heads is a small town located on the southeastern coast of Australia, 250km southwest of Sydney, and meteorological records are available for there since 1876. However, it was found that the temperature data were inconsistent prior to 1910 (probably due to different instrumentation) and therefore the analyses were only carried out using the data since 1910.
The Moruya Heads station is a particularly valuable record and it has been located at the same location since 1876. Furthermore, it is is located on a coastal promontory without any significant changes in nearby buildings (the present nearby building was constructed in 1910) or vegetation over that period. Until the 1970s the station location was used as a coastal pilot station and the area has since been administered by the NSW National Parks and Wildlife Service. It is is located near a small village so is without any urban influences.
The date of introduction of the standard Stevenson Screen at Moruya Heads is not known, but was probably before 1910. Different temperature enclosures (eg the Glaisher stand) in the early years may have resulted in inconsistent records. Plots of the annual mean maximum and minimum temperatures indicates that the data prior to about 1910 was inconsistent with later data and therefore, in this analysis, only data since 1910 were used.
The data used are the raw data (as observed) without any adjustments and were obtained from the website of the Australian Bureau of Meteorology www.bom.gov.au
Graphical plots are presented below of monthly values of mean maximum and mean minimum temperatures for each of the 12 months. Plots of annual values of mean, mean maximum, mean minimum, extreme maximum and extreme minimum temperatures are also presented.
Polynomial (non-linear) regression lines are fitted to each of the plots. These regression lines indicate the variation in temperature trends over the past 105 years.
Monthly Mean Maximum Range
Monthly Mean Minimum Range
Annual Extreme Maximum
Annual Extreme Minimum
– The plots indicate that the data since 1910 are consistent, with no sudden “steps” (which could indicate a change in instrumentation or location) or “kinks or bends” (which could indicate local changes such as trees or buildings).
– There is a significant variation in the temperature trends between day (maximums) and night (minimums) and between seasons. No consistent pattern of variation in the trends is evident.
– Cyclic trends are observed for most months with peaks around 1920 and 2010 and a trough around 1960. In most months the temperature trends are found to decrease (ie lower temperatures) between about 1920 and 1960. This was followed by increasing temperatures up until around 2000. These cycles are consistent with cycles of around 80 years observed at other locations worldwide.
– In the 15 years from 2000 the monthly mean temperatures were found to be steady or slightly falling .
– Annual extreme maximum and minimum temperature trends at Moruya Heads are available only since 1957. This short period of records is meaningless as an indicator of long-term temperature trends. However, it is seen that extreme maximum temperatures were fairly constant over the 58-year period while extreme minimum temperatures increased by about 1°C.
– Annual mean maximum and minimum temperature trends, which amalgamate the seasonal variation in temperatures, are of less meaning than are the monthly trends. The annual mean minimum trend shows a strong cyclic variation with peaks around 1920 and 2000 and a trough around 1960. The annual mean maximum cyclic variation is less evident but there is a trough around 1930 and a peak around 2010.
This article was written by Brian Gunter of Narooma, NSW. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.