Water monitoring
Rainfall
About rainfall
The Auckland Region's fresh and geothermal water resources are fed by rainfall. Rain falling directly feeds streams, rivers, lakes and wetlands, and infiltrates to recharge groundwater aquifers.
Rainfall distribution is predominantly governed by topography. Elevated areas of the Waitakere and Hunua Ranges, Hotea Catchment and One Tree Hill, all receive high annual rainfall when compared with other parts of the region. Areas of low rainfall occur in proximity to the Kaipara and Manukau Harbours, and over the Hauraki Gulf. This is evident in rainfall records, which show an average annual rainfall in the Waitakere Ranges of 2030mm while Tiritiri Matangi Island receives only 950mm. An annual rainfall distribution map for the region is shown below.
rainfall distribution map
What we measure
The ARC measures rainfall at 29 sites throughout the Auckland Region. Of these 19 are automatic with the data sent electronically to our Auckland office. The remaining 13 are manually read daily gauges.
For the location of rainfall monitoring sites go to Environmental Data online, up to date and historical data is available to be viewed and downloaded.
How rainfall is measured
Rainfall is measured automatically by tipping bucket rain gauges. Inside the gauge are two buckets on a pivot, which tip each time 0.5mm of rain falls. These tips are then recorded by a data logger which assigns a date and time to each tip. This information can then be retrieved back in our Auckland office via telemetry. These automatic gauges are more useful than daily read manual gauges, as they tell us the rate at which the rainfall fell. This is known as rainfall intensity. For example, heavy rain falling over a short time period will have very different environmental effects to light rain falling all day. The total amount for the day, however, could be very similar.
Rainfall intensity impacts on flooding and stormwater design, erosion and sediment generation.
tipping bucket rain gauge
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