About the average rainfall maps
Australian average rainfall maps are available for annual and seasonal rainfall. Long-term averages have been calculated over the standard 30-year period 1961-1990. A 30-year period is used as it acts to largely smooth out the year-to-year variations of climate.
Interpreting the analyses
The average rainfall maps can be used in conjunction with the rainfall trend maps to provide an indication of how a trend compares to the long-term average. For example, what might seem like a large trend in a particular region might not be all that significant if the average rainfall is very large.
Approximately 6000 stations are used in the average rainfall maps. All input station data underwent a high degree of quality control before analysis, and conform to WMO (World Meteorological Organization) standards for data quality. There are many more sites included in the average rainfall maps than the rainfall trend maps because the trend maps require open sites with much longer, homogeneous records.
To produce the average maps, station data were analysed onto regular grids using the ANU (Australian National University) 3-Dimensional Spline (surface fitting algorithm). As part of the analysis process a 0.025 degree (approximately 2.5 km) resolution digital elevation model (DEM) was used. Because the average maps take into account topography, and are based on many more input stations, they are able to provide much finer detail than the trend maps.
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.