A brief summary of climate and hydrological conditions in the region.

This service is only updated during periods in which closer monitoring is required (regardless of time of the year), in recognition that there is potential for dry spells, or irregular hydrological recharging. It does not define an official council position on drought or drought declaration.

Updated 9 September 2022. 

Next update due when there is a significant change of conditions, as the situation evolves.

Background

Very significant, widespread rain fell in the region during winter. The western side of the ranges had the wettest winter on record by a far margin, even for long-term recording sites going back to almost 150 years of observations. This is a very significant wet phase of a climate signal, amplified by the fact that summer was also the wettest on record for both Wellington and the Wairarapa.

In the Wellington case, various slips developed as a result of the extreme saturation levels of the soil which had already carried on the abnormal moisture from summer. For the Wairarapa, the winter rainfall was less impressive but still above average.

As a result, soils and underground water for the Wairarapa remained reasonably replenished and within normal levels for the beginning of spring. Some farms experienced damage and losses due to excessive winter rain, after a lack of summer drying.

Current situation

The global climate remains ‘phase-locked’ into a semi-permanent La Niña mode. This cooling of the Equatorial Pacific contributes to more marine heatwaves around New Zealand (via the oceanic circulation). This helps explain the excessive rainfall and remarkable incursion of atmospheric river events during both summer and winter.

Thanks to the background global warming and the semi-permanent La Niña, 2022 was the second consecutive year with the warmest winter on record for both our region and New Zealand as a whole.

Meteorological outlook

Most dynamical climate models are predicting the persistence of high pressure south-east of New Zealand into spring, continuing with significantly warmer than average seasonal temperatures.

A prevailing La Niña easterly flow is expected to alternate with strong westerlies at times. Humidity corridors (atmospheric rivers) under the influence of moist tropical air masses are expected to continue to occur, albeit less frequently in spring.

A continuing negative phase of the Indian Ocean Dipole can also contribute towards above normal rainfall on the western coast and about normal in the Wairarapa, with a large month-to-month variability expected.

Climate change

The ‘normal’ longer-term water balance is becoming increasingly hard to maintain quite possibly due to climate change influences, and increased high frequency climate variability, with more unreliable weather patterns.

Droughts are expected to become more severe and frequent in the Wellington region, particularly in the Wairarapa. Even if international climate policy efforts successfully contain global warming under 1.5-2 degrees (the Paris Agreement’s ambition), it is important that we enhance our water resilience and be prepared for a “new normal” climate pattern, significantly drier than in the past.

We note that the warming temperatures also mean that evapotranspiration will greatly increase. There is some evidence that our soils are getting drier, and groundwater storage may be decreasing, in the long-term.

View the latest national drought index state

Browse the data

Anomaly Maps

How different has recent rainfall/soil moisture been compared with the same time in previous years?

30 Day Rainfall Anomaly

90 Day Rainfall Anomaly

1 Day Soil Moisture Anomaly

30 Day Soil Moisture Anomaly

 

Site-specific graphs

Cumulative rainfall/soil moisture totals for indicator sites compared with historical averages and other recent years. 
Area Rainfall Soil Moisture
Kapiti Coast (lowland) Otaki at Depot  
Kapiti Coast (high altitude) Penn Creek at McIntosh  
Porirua Horokiri Stream at Battle Hill  
Wellington City Kaiwharawhara Stream at Karori Reservoir  
Hutt Valley (upper catchment) Hutt River at Kaitoke Headworks  
Upper Hutt Upper Hutt at Savage Park Upper Hutt at Savage Park AQ
Wainuiomata Wanuiomata River at Wainui Reservoir  
Wairarapa (high altitude) Waingawa River at Angle Knob  
Wairarapa Valley (north) Kopuaranga River at Mauriceville  
Wairarapa Valley (Masterton) Ruamahanga River at Wairarapa College Wairarapa College AQ
Wairarapa Valley (south) Tauherenikau River at Racecourse Tauherenikau River at Racecourse
Wairarapa (north-eastern hills) Whareama River at Tanawa Hut Whareama River at Tanawa Hut
Wairarapa (south-eastern hills) Waikoukou at Longbush Waikoukou at Longbush
Updated September 9, 2022 at 2:59 PM

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Phone:
0800496734
Email:
info@gw.govt.nz