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 20 December 2022. 

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

Background

After a very wet year overall, spring rainfall remained above average over the Wairarapa. Even though December entered a drier and more mixed pattern, soil moisture levels remain within normal, with significant thunderstorms developing in the lead up to Christmas.

Current situation

The global climate remains ‘phase-locked’ into a mature La Niña, coupled with a positive Southern Annular Mode. This translates into more frequent marine heatwaves around New Zealand, with a predominantly warm and humid north-easterly flow. This pattern helps explain the positive rainfall anomalies in the Wairarapa observed during most of 2022, with significant ‘atmospheric river’ events.

Meteorological outlook

Most dynamical climate models are predicting the persistence of high pressures south-east of New Zealand into summer, which will lead to continuing warmer than average seasonal temperatures. A prevailing La Niña easterly flow is expected to alternate with westerlies at times. Humidity corridors (atmospheric rivers) under the influence of moist tropical air masses are expected to continue to affect the region over summer.

There is a high likelihood that at least two ex-tropical cyclones will affect the country during the warm season. For the Wairarapa, the total rainfall accumulation during the warm season will also largely depend on the formation of localised thunderstorm activity, which is typical of humid summers under north-easterly flows.

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 20, 2022 at 10:50 AM

Get in touch

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