Information icon

Northland is at COVID-19 ORANGE setting. Get information about our services during the protection framework settings.

Arrow icon

May 2021 climate report

22 Jun 2021, 11:00 AM

Summary

  • Broadly speaking, May 2021 was a dry month for the region
  • Rainfall over longer timeframes (the previous 6 months) can be categorised as “Moderately Dry” to “Severely Dry” in eastern areas
  • River flows were generally lower than normal for May, particularly in the northern sub-catchments of the Wairoa River
  • Groundwater levels for the month were below normal for most areas except Aupouri and Ruawai, and “Very Low” in Whangarei, Poroti and Mangawhai
  • Soil moisture is near average for this time of year at all NIWA climate stations
  • The NIWA three-month outlook is for near normal rainfall

Outlook

June to August:

The long-range outlook for June to August 2021 is for near normal rainfall, soil moisture and river flows for Northland. Temperature is still likely to be above normal during this period.

NIWA Temperature, Rainfall, Soil Moisture and River Flows probabilities for June to August 2021

  Temperature Rainfall Soil moisture River flows
Above average 50 30 20 20
Near average 45 45 40 45
Below average 05 30 40 35

Rainfall

 May 2021 was a dry month for Northland overall with rainfall ranging from between 30% of typical rainfall to 75% of typical rainfall. There were no significant weather events during the month.

NRC Standardised Precipitation Index is an indicator used to compare rainfall received over extended periods compared to typical rainfall over those periods. This index indicates that over a 6-month period, rainfall across the region has been “Moderately Dry” to “Severely Dry” in eastern areas. Over a 12-month time frame, rainfall has been “Near Normal” in most areas with the exception of the Hakaru catchment (near Mangawhai) which is classified as “Severely Dry” over this period.

Rainfall % median maps for May 2021 and for the three months of Autumn 2021

 

SPI Index map for 6 and 12 months to the end of May 2021

 

Rainfall deficit values (mm)

Site End Date 1 Month 3 Months 6 Months 12 Months
Kaitaia Aero Ews May 2021 -55.67 -121.87 -131.50 -57.40
Kerikeri Ews May 2021 -65.59 -75.91 -137.40 -81.95
Kaikohe Aws May 2021 -63.10 -121.88 -133.41 237.28
Whangarei Aero Aws May 2021 -38.29 -50.36 -100.78 231.24
Hokianga Harbour at Omapere/Opononi May 2021 -28.53 -11.84 -41.50 -25.54
Dargaville 2 Ews May 2021 -33.34 -23.92 -73.03 -42.86
Awaroa at Wallace Road May 2021 -42.99 -4.24 -44.24

-7.2

River flow

River flows during May 2021 were below normal across most of the region, and particularly low in the northern sub-catchments of the Wairoa River with flow in the categories “Very Low” and “Extremely Low” here (5-10th and 0-5th percentiles respectively).                                                                                                                                                                                                                                                  

Flow map May 2021

Groundwater

During May 2021 Groundwater levels were “Normal” or “Above Normal” in the Aupouri, and Ruawai groundwater systems, “Below Normal” in Taipa, Russell, Kaikohe and “Very Low” in Whangarei, Poroti and Mangawhai.    

Northland aquifer status table

Groundwater System

Status (May 21)

Percentile

Aupouri

Above Normal

>60th

Taipa

Below Normal

25th-40th

Russell

Below Normal

25th-40th

Kaikohe

Below Normal

25th-40th

Whangarei

Very Low

5-10th

Poroti

Very Low

5-10th

Mangawhai

Very Low

5-10th

Rauwai

Normal

40-60th

 

Northland aquifer status map May 2021

 

Soil moisture deficits

NIWA water balance modelling indicates soil moisture deficit is near normal at all NIWA climate stations, and close to or at field capacity. “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).

Soil moisture deficit at NIWA climate stations

NIWA Climate Station

Observed Soil moisture deficit (mm) as of 08/06/2021

Average 8 Jun soil moisture deficit

Difference between Expected and Average

Kaitaia

0 mm

0 mm

0

Kerikeri

10 mm

0 mm

10

Whangarei

10 mm

0 mm

10

Kaikohe

20 mm

0 mm

20

Dargaville

-10mm

0 mm

-10

Warkworth

0 mm

-10 mm

10

 

 

 

 

 

NIWA soil moisture deficit plots