About Rainfall Data

Introduction

Rainfall: Rainfall includes all forms of water particles, whether liquid (for example, rain or drizzle) or solid (hail or snow), that fall from clouds and reaches the ground. The rain gauge is the standard instrument for recording rainfall, which is measured in millimetres. Rainfall is generally observed daily at 9 am local time - this is a measure of the total rainfall that has been received over the previous 24 hours. More frequent observations of rainfall are also available for selected sites.

Precipitation is most commonly termed rain and includes rain, drizzle, hail and snow. The type of precipitation (when observed) is recorded along with the amount of precipitation. Observations of daily rainfall are nominally made at 9 am local clock time and record the total precipitation for the preceding 24 hours. Other, more frequent, observations are also made at some stations. If, for some reason, an observation is unable to be made, the next observation is recorded as an accumulation, since the rainfall has been accumulating in the rain gauge since the last reading. Within the monthly rainfall product, where an accumulation crosses a monthly boundary the allocation of accumulated precipitation to the months in which it fell has been done if feasible.

Prior to 1974 rainfall was measured to the nearest point (one hundredth of an inch). Since then, observations have been made to the nearest 0.2 mm, although some observations are read to 0.1 mm. The majority of rainfall observations are made by volunteers, and reported monthly to the Bureau. Data may not be available immediately at the end of the month. There are historical rainfall data for more than 19,000 stations, with approximately 8000 stations currently making observations.

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General information about historical observations

Data Quality

Climate data pass through a number of stages in quality control which occurs over a period of time. Data are only included in this product if no errors have been detected at the time. Data which have not yet completed the routine quality control process are marked accordingly.

Gaps and missing data

Very few stations have a complete unbroken record of climate information. A station may have been closed, reopened, upgraded to a full weather station or downgraded to a rainfall only station during its existence causing breaks in the record for some or all elements. Some gaps may be for one element due to a damaged instrument, others may be for all elements due to the absence or illness of an observer, or perhaps the failure of an automatic weather station.

Instruments and observational practices

Historically, if a station moved a relatively short distance (within about 1 to 2 km) it may, but not always, have continued to use the same station number. Changes may have occurred in instrumentation and/or observing practices over the period included in a dataset, which may have an effect on the long-term record. In recent years many stations have had observers replaced by Automatic Weather Stations, either completely or at certain times of the day.

Latitudes and longitudes

The accuracy of the geographic coordinates of a station has generally improved since the Bureau started taking observations. In the early days the position of a station was usually estimated from a map. In recent years, as an open station was inspected the location was checked (and if necessary corrected) using GPS (Global Positioning System).

Time

For a part of the year some Australian States adopt Daylight Savings Time (DST). The changeover dates vary from State to State and year to year. More information can be found on the following page:
http://www.bom.gov.au/climate/averages/tables/daysavtm.shtml
Observing practices, such as whether an observation was made according to local standard time or local clock time (incorporating DST if applicable), have undergone some changes since observations began. More information is available at:
http://www.bom.gov.au/climate/averages/tables/dst_obs.shtml

Copyright

The copyright for any data is held in the Commonwealth of Australia and the purchaser shall give acknowledgement of the source in reference to the data. Apart from dealings under the copyright Act, 1968, the purchaser shall not reproduce, modify or supply (by sale or otherwise) these data without written permission. For further information please refer to the Bureau of Meteorology's Copyright Notice.

Liability

While every effort is made to supply the best data available this may not be possible in all cases. We do not give any warranty, nor accept any liability in relation to the information given, except that liability (if any), that is required by law.

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Page updated: 28 April 2010