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Source: NIWA – National Institute of Water and Atmospheric Research

Ominously large and bloated with moisture, angry clouds sweep across the Fiordland coast.

Winds drive the storm system higher and torrential rain begins thudding into the earth below. It doesn’t take long before heavy drops start falling plumb into the mouth of the Takahe Valley rain gauge, in the Murchison Mountains just west of Lake Te Anau.

The raindrops are about to make their mark at a national scale.

In a matter of seconds, they will trigger a response from the automated gauge and be registered in an ever-growing climate database that plays a key role in decision making across the country.

The raindrops falling at NIWA’s Takahe Valley weather station collect in a small, seesaw-like receptacle called a tipping bucket. Bit by bit, the water level inches upward. The bucket over balances, dumps its load and resets for another take.

A datalogger records the tip and pings the information to a server at NIWA’s Christchurch office. From there it travels along a high-speed network to NIWA’s Wellington office, where it is automatically entered into long-term storage in New Zealand’s national Climate Database – more commonly known as CliDB.

For a meteorologist, CliDB is the motherlode. It stores weather data from all over New Zealand, Antarctica and the Pacific Islands. The earliest recordings are from the mid-1800s, with the latest information flowing in from a network of hundreds of stations like that in Takahe Valley.

The database is growing fast. If it is raining hard in the Murchison Mountains, the automated rain gauge generates a measurement every six seconds. Ten minute and hourly readings are also taken – rain, hail or shine. Weather stations, of course, measure far more than just rainfall. Sensors put together by NIWA’s Instrument Systems division simultaneously record temperature, wind speed, air pressure and humidity. Some specialist stations measure solar radiation, and every instrument is busy feeding its own stream of data into the network.

With stations dotting the country and weather fronts hitting all points of the compass, the numbers quickly add up. In January alone, more than 1.5 million new rainfall data points flooded into CliDB.

In total, CliDB is connected to more than 600 weather stations – a network that stretches out across New Zealand, north into the Pacific and as far south as Antarctica. Many of the facilities are maintained by other agencies, such as MetService, the Department of Conservation and regional councils.

The database also incorporates a host of additional weather information provided by sources ranging from drifting ocean buoys and shipping vessels to historic observations gathered from lighthouses or aircraft.

Readings from seven key sites – Auckland, Masterton, Wellington, Nelson, Hokitika, Lincoln and Dunedin – are particularly important. Stations at these locations have been benchmarking New Zealand’s average annual temperature since 1909. NIWA’s seven station temperature series has confirmed NZ’s average annual temperature has increased by about 1°C over the past 100 years.

NIWA is the custodian and the curator of all the information flooding into CliDB. The data is rigorously quality controlled and audited to international standards, with machine learning playing an increasingly significant role as computers are programmed to hunt for gaps and flag anomalies in the dataset.