About the rainfall trend maps

Analyses available

Australian and regional rainfall trend maps are available for annual and seasonal rainfall, covering periods starting from the beginning of each decade from 1900 to 1970. These different starting times demonstrate the importance of the analysis period on rainfall trend values. For example, the post-1900 maps look quite different to the post-1970 maps. Prior to 1900 the rainfall network is generally too sparse for reliable analysis, and analysis periods starting after 1970 are considered too short to calculate meaningful trend values.

Interpreting the analyses

The trend maps are a useful way to compare how the rainfall 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 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, because rainfall is such a variable element, trend values are highly dependent on the start and end dates of the analysis. Consequently trend maps starting in different decades can look remarkably different. 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

Mean rainfall timeseries are calculated using a high-resolution gridded dataset developed for the Australian Water Availability Project (AWAP). The dataset uses topography-resolving analysis methods applied to all available monthly rainfall data passed by a series of internal quality tests. The resulting analyses have a resolution of approximately 5 km x 5 km.

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.

Representative locations of rainfall stations included in the trend maps

Further information

Jones, D.A., Wang, W. and Fawcett, R. (2009). High-quality spatial climate data-sets for Australia. Australian Meteorological and Oceanographic Journal, 58, 233–248.

Full electronic copies of papers published in the Australian Meteorological Magazine, now known as the Australian Meteorological and Oceanographic Journal, are available online.