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 21 December 2021. Next update due when there is a significant change of conditions, as the situation evolves.

Background

After a very dry late spring and a very wet first half of December, the Wairarapa soil moisture and drought indicators went back within the normal range prior to Christmas. The New Zealand drought index from NIWA has been very dry for the Wairarapa, but as of 21 Dec, only the eastern coast remained dry.

As the warm season progresses, however, the tendency is for the dryness phase to amplify again, depending on the duration of summer dry spells, and how much above average the temperatures (and evaporation) will be.

Current situation

La Niña is now fully evolved, with significantly warmer than average Sea Surface Temperatures (SST) around New Zealand, and a mostly positive Southern Annular Mode (SAM).

These combined conditions tend to amplify the classic La Niña signature of above average temperatures with greater humidity, dry spells and thunderstorms.

Meteorological outlook

Most dynamical climate models are predicting a vigorous blocking anticyclone establishing east of New Zealand later into summer, with significantly warmer than average seasonal temperatures.

A prevailing La Niña north-easterly flow is expected to alternate with strong westerlies, early in the season. Extended dry periods are possible especially in the east, albeit mostly muggy under the influence of moist tropical air masses.

Rainfall distribution should continue to be irregular, with further extreme rainfall events likely under both easterly and westerly flows. As the season evolves, more settled warm and humid weather and thunderstorms are 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 December 21, 2021 at 12:57 PM

Get in touch

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