While the North Island and the top of the South Island have been soaked in recent weeks, farmers at the bottom of the South Island are "crying out for rain".
According to Niwa, Southland and Otago received less than half the average rainfall for last month.
The lowest rainfalls in the country last month were recorded in Milford Sound, Puysegur Point, Dunedin, Manapouri, Queenstown, Lumsden, Gore, Invercargill, Balclutha and Tiwai Point.
Dunedin received its lowest rainfall since records began at the Musselburgh site in 1918, with 9mm recorded last month, compared with an average of 81mm.
The city was the fourth-driest southern site in December, after Clyde (7mm), Gore (8mm) and Manapouri (8mm).