November 2021 climate report

Summary

• Rainfall during November 2021 was near normal in comparison to typical November rainfall
• River flows were universally “Above Normal” across the region and similar to September/October 2021
• Groundwater levels were “Above Normal” in most groundwater systems
• Soil moisture is near normal or wetter than normal for this time of year
• The long-range outlook predicts near normal rainfall for the next three months, but warmer than typical temperature is very likely. NIWA note that heat wave conditions are possible over summer

Outlook

December 2021 to February 2022:

The NIWA long-range outlook for December 2021 to February 2022 calls for near normal rainfall, soil moisture and river flows, but above normal temperatures. NIWA note that La Nina conditions have developed in the equatorial pacific. The likelihood of ex tropical cyclones landing in our neck of the woods is generally increased in La Nina conditions. Typically, over the long term in New Zealand, an average of one ex-tropical cyclone reaches New Zealand shores per year. This is increased to one to two ex-tropical cyclones for 2021/22 which is considered an “Elevated” risk. For further details please refer to NIWA’s tropical cyclone outlook:

See the seasonal climate outlook on NIWA's website

NIWA Temperature, Rainfall, Soil Moisture and River Flows probabilities for the period Dec 2021 to Feb 2022

Expressed as % likelihood for either Above Average, Near Average or Below Average conditions.

Rainfall

Rainfall totals recorded November 2021 were fairly typical in comparison to long term November rainfall. The Northland region averaged 69.9mm when we would expect around 78.0mm regionally (90% of what would be expected in November). Areas receiving the most rain were the hill country sites around the Mangamukas and west of Kaikohe – areas spanning north and south of the Upper Hokianga harbour. The Whawharu site at Topu B near Taheke had 161mm of rain, Waimamaku at Wekaweka Road 143.5mm, Takahue at Saddle Road 127.5mm and Te Puhi at Mangakawakawa (Mangamukas) 112mm. Inland areas north and south of the Whangarei harbour had the least rain as well as the very Far North. Okarika at Rowland Road in the Hikurangi Swamp area had only 35.5mm in November followed just to the north by the Waiharakeke at Okaroro Road at 38.5mm, Pouto Point on 39.5mm and Cape Reinga on 40mm. One severe weather warning was issued by MetService on the 14/11/2021 and only minor flooding occurred in the commonly affected areas around Oruru and Kaeo.

3-month SPI (Standardised Precipitation Index) values for the last three months reflect the very wet conditions experienced in September/October/November 2021 (see map below).

Rainfall % median maps for November 2021

SPI Index map for 3 (SPI3) and 6 months (SPI6) to the end of November 2021

Rainfall deficit values (mm)

Negative values represent rainfall deficit, positive values represent rainfall in excess of “typical” rainfall

River flow

River flows during November 2021 were similar to September/October and universally above normal for the month compared to average November flow. This is largely driven by showers through the month and the continuation of wet ground conditions from previous months.

Flow map November 2021

Groundwater

During November 2021 groundwater levels were “Normal” or “Above Normal” at all locations. A wet winter and spring in most areas has enabled groundwater to recover well from low summer levels.

Northland aquifer status table for November 2021

Northland aquifer status map November 2021

Soil moisture deficits

NIWA water balance modelling indicates soil moisture conditions are wetter than normal at most NIWA climate stations. Soil moisture has dropped below field capacity indicting that minor rainfall events are unlikely to lead to significant river runoff. This is typical for this time of year. “SMD is calculated based on incoming daily rainfall (mm), outgoing daily potential evapotranspiration (PET, mm), and a fixed available water capacity (the amount of water in the soil 'reservoir' that plants can use) of 150 mm” (NIWA).