Climate

The  table and graphs below show average monthly figures for a range of climatic factors over the 30-year period 1981–2010.[1] These figures are measured at the weather station at Rotorua Airport.

Climate factor Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Sunshine hours 243 206 200 170 145 119 131 152 155 191 200 216 2128
Mean daily max temp (°C) 23 23 21 18 15 13 12 13 15 16 19 21 17
Mean temp (°C) 18 18 16 13 11 8 8 8 10 12 14 16 13
Mean daily min temp (°C) 13 13 11 9 6 4 4 4 6 8 9 12 8
Growing degree days (hours) 234 224 181 102 48 15 8 8 30 65 109 189 1214
Humidity (%) 79 81 81 83 87 88 87 86 82 80 77 79 83
Rainfall (mm) 93 94 99 107 117 136 135 131 109 112 94 114 1342
Wet days (>=1mm rain) 8 7 9 8 9 11 11 12 11 11 9 10 117
Ground frost days 0 0 0 2 5 9 12 10 5 2 1 0 46
Winter chill hours 0 0 0 55 119 177 214 190 115 0 0 0 870

 

Some key points arising from this table:

  • Sunshine hours are at their maximum in January, at 243 hours, and typically reach their lowest in June, with 119 hours.
  • Temperature: the annual average temperature ranges from 8–18°C with the average maximum temperature being 23°C and the average minimum being 4°C.
  • Growing degree days (above a 10 degree baseline) vary during individual years from under 1000 hours up to about 1400 hours, with an average across the 30-year time period of 1214 hours.
  • Humidity ranges from 79 percent in summer up to 88 percent in June, with an annual average of 83 percent.
  • Rainfall is measured at Rotorua Airport but varies significantly across the catchment from 1342 mm at Rotorua Airport to around 2400 mm on the Mamaku plateau.
  • Frost: Rotorua (airport) has about 46 ground frosts and 20 air frosts per year on average. Importantly, there is also a risk of early-season ground frosts in October, November and December, and late-season ground frosts in March and April, which can adversely affect many crops.
  • Winter chill hours: Rotorua receives an annual average of 870 hours of winter chilling below 7°C.

The following graphs show temperature and rainfall figures in the Lake Rotorua catchment.

 

 

Rotorua compared to other growing areas

To provide context of how Rotorua compares with other growing areas in New Zealand, below is a table comparing select climate variables in these areas averaged over the years 1981–2010:[2]

 

Rotorua’s rainfall of 1342 mm is the highest of the locations listed, but this does not represent the entire catchment well as the Rotorua Airport location receives the lowest rainfall in the Lake Rotorua catchment. Rainfall levels increase moving westward to the Mamaku plateau, which can receive up to 2400 mm per year.

While sunshine hours at 2128 hours annually is in the mid-range of the other regions reported, the lower mean temperature of 13°C results in lower growing degree days, essentially a shorter growing season. This shorter growing season coupled with higher rainfall and hence humidity creates a limiting environment for many horticultural crops.

Wind

Although the prevailing windflow over northern New Zealand is west to southwest, winds over the Bay of Plenty region are modified by the local topography.

Wind roses (showing mean annual frequency of surface wind speed and direction based on hourly observations) for four sites in Bay of Plenty are shown below [3]. Winds from the west and southwest prevail at Mt Te Aroha (elevation 951 m) and at Tauranga, while at Whakatane, north-westerly and south-westerly winds are the most frequent.

At Rotorua, the prevailing wind is north-easterly, but winds from between south and west are also common.

Wind speed

The average daily wind speed in Rotorua varies little throughout the year, averaging around 12 km/hr with a slight increase during spring to 13–15 km/hr [4].

 

References:
[1, 2, 4] Cliflo Database, NIWA

[3] The Climate and Weather of the Bay of Plenty, 3rd ed. NIWA 2013