About the Temperature Trend Maps
Analyses available
Australian and State temperature trend maps are available for annual mean temperatures starting at the beginning of each decade from 1910 to 1970, and for seasonal mean temperatures starting in 1950, 1960 and 1970. This is because the dataset on which the annual analyses are based starts in 1910 (prior to this time Australian temperature records are sparse and some are measured in non-standard ways). Seasonal temperature analyses are limited to the post-1950 era because they are based on a daily temperature dataset and there is currently only a limited amount of digitised daily temperature data prior to 1950. Analysis periods starting after 1970 are considered too short to calculate meaningful trend values.
Separate trend maps are available for maximum, mean and minimum temperature, as well as diurnal temperature range (DTR). Mean temperatures are the simple average of the maximum and minimum temperatures, while DTR represents the difference between maximum and minimum temperatures.
Interpreting the analyses
The trend maps are a useful way to compare how the temperature has changed in different regions of Australia over time. However, they need to be interpreted with caution. Trend values have been determined from a linear (straight line) fit to the data, but the change indicated may not have been gradual. For example, a calculated trend could be due to a relatively rapid "step" change, with the remainder of the series being fairly flat (see some of the timeseries graphs). Also, for regions and seasons in which the year-to-year changes are large, the value of the calculated trend will depend on the start and end values of the data series, potentially misrepresenting the background trend. Users are advised to keep in mind the period over which trend values have been calculated and interpret them alongside the timeseries of spatially averaged values.
In addition, the trend values calculated here using past observations should not be used to imply future rates of change. Due to the complex interactions between the natural and human drivers of climate change and variability, the climate of any location is always changing. Future rates of change will depend on how these drivers interact in future, which will not necessarily be the same as in the past.
Data used
The temperature trend maps are calculated from homogeneous or "high-quality" temperature datasets developed for monitoring long-term temperature trends and variability (see maps below). Where possible, each station record in these datasets has been corrected for data "jumps" or artificial discontinuities caused by changes in observation site location, exposure, instrumentation or observation procedure. This involves identifying and correcting data problems using statistical techniques, visual checks and station history information (metadata).
Please note that any use of these data should be acknowledged to the Bureau of Meteorology. Apart from the purposes of study, research, criticism and review, no part of these data may be reproduced, or redistributed for any commercial purposes, or distributed to a third party for such purpose, without written permission from the Director of Meteorology.
Locations of records included in Australia's high-quality annual temperature dataset
Locations of records included in Australia's high-quality daily temperature dataset
Further information
Della-Marta, P.M., Collins, D.A. and Braganza, K. 2004. Updating Australia's high-quality annual temperature dataset. Australian Meteorological Magazine, 53, 75-93.
Jones, D.A. and Trewin, B.C. 2000. The spatial structure of monthly temperature anomalies over Australia. Australian Meteorological Magazine, 49, 261-276.
Jones, D.A. and Trewin, B.C. 2002. On the adequacy of digitised historical Australian daily temperature data for climate monitoring. Australian Meteorological Magazine, 51, 237-250.
Torok, S.J. and Nicholls, N. 1996. A historical annual temperature dataset for Australia. Australian Meteorological Magazine, 45, 251-260.
Trewin, B.C. 2001. Extreme temperature events in Australia. PhD Thesis, School of Earth Sciences, University of Melbourne, Australia.
Full electronic copies of papers published in the Australian Meteorological Magazine, now known as the Australian Meteorological and Oceanographic Journal, are available online.
